@spec add_error(t(), atom(), String.t(), Keyword.t()) :: t()

Adds an error to the changeset.

An additional keyword list keys can be passed to provide additional contextual information for the error. This is useful when using traverse_errors/2 and when translating errors with Gettext

Examples

iex> changeset = change(%Post{}, %{title: ""})
iex> changeset = add_error(changeset, :title, "empty")
iex> changeset.errors
[title: {"empty", []}]
iex> changeset.valid?
false

iex> changeset = change(%Post{}, %{title: ""})
iex> changeset = add_error(changeset, :title, "empty", additional: "info")
iex> changeset.errors
[title: {"empty", [additional: "info"]}]
iex> changeset.valid?
false

iex> changeset = change(%Post{}, %{tags: ["ecto", "elixir", "x"]})
iex> changeset = add_error(changeset, :tags, "tag '%{val}' is too short", val: "x")
iex> changeset.errors
[tags: {"tag '%{val}' is too short", [val: "x"]}]
iex> changeset.valid?
false

@spec apply_action(t(), atom()) :: {:ok, Ecto.Schema.t() | data()} | {:error, t()}

Applies the changeset action only if the changes are valid.

If the changes are valid, all changes are applied to the changeset data. If the changes are invalid, no changes are applied, and an error tuple is returned with the changeset containing the action that was attempted to be applied.

The action may be any atom.

Examples

iex> {:ok, data} = apply_action(changeset, :update)

iex> {:ok, data} = apply_action(changeset, :my_action)

iex> {:error, changeset} = apply_action(changeset, :update)
%Ecto.Changeset{action: :update}

@spec apply_action!(t(), atom()) :: Ecto.Schema.t() | data()

Applies the changeset action if the changes are valid or raises an error.

Examples

iex> changeset = change(%Post{author: "bar"}, %{title: "foo"})
iex> apply_action!(changeset, :update)
%Post{author: "bar", title: "foo"}

iex> changeset = change(%Post{author: "bar"}, %{title: :bad})
iex> apply_action!(changeset, :update)
** (Ecto.InvalidChangesetError) could not perform update because changeset is invalid.

See apply_action/2 for more information.

@spec apply_changes(t()) :: Ecto.Schema.t() | data()

Applies the changeset changes to the changeset data.

This operation will return the underlying data with changes regardless if the changeset is valid or not. See apply_action/2 for a similar function that ensures the changeset is valid.

Examples

iex> changeset = change(%Post{author: "bar"}, %{title: "foo"})
iex> apply_changes(changeset)
%Post{author: "bar", title: "foo"}

@spec assoc_constraint(t(), atom(), Keyword.t()) :: t()

Checks the associated field exists.

This is similar to foreign_key_constraint/3 except that the field is inferred from the association definition. This is useful to guarantee that a child will only be created if the parent exists in the database too. Therefore, it only applies to belongs_to associations.

As the name says, a constraint is required in the database for this function to work. Such constraint is often added as a reference to the child table:

create table(:comments) do
  add :post_id, references(:posts)
end

Now, when inserting a comment, it is possible to forbid any comment to be added if the associated post does not exist:

comment
|> Ecto.Changeset.cast(params, [:post_id])
|> Ecto.Changeset.assoc_constraint(:post)
|> Repo.insert

Options

• :message - the message in case the constraint check fails, defaults to "does not exist"
• :name - the constraint name. By default, the constraint name is inferred from the table + field. If this option is given, the field argument only indicates the field the error will be added to. May be required explicitly for complex cases
• :match - how the changeset constraint name is matched against the repo constraint, may be :exact, :suffix or :prefix. Defaults to :exact. :suffix matches any repo constraint which ends_with? :name to this changeset constraint. :prefix matches any repo constraint which starts_with? :name to this changeset constraint.

@spec cast(
  Ecto.Schema.t() | t() | {data(), types()},
  %{required(binary()) => term()} | %{required(atom()) => term()} | :invalid,
  [atom()],
  Keyword.t()
) :: t()

Applies the given params as changes on the data according to the set of permitted keys. Returns a changeset.

data may be either a changeset, a schema struct or a {data, types} tuple. The second argument is a map of params that are cast according to the type information from data. params is a map with string keys or a map with atom keys, containing potentially invalid data. Mixed keys are not allowed.

During casting, all permitted parameters whose values match the specified type information will have their key name converted to an atom and stored together with the value as a change in the :changes field of the changeset. If the cast value matches the current value for the field, it will not be included in :changes unless the force_changes: true option is provided. All parameters that are not explicitly permitted are ignored.

If casting of all fields is successful, the changeset is returned as valid.

Note that cast/4 validates the types in the params, but not in the given data.

Options

• :empty_values - a list of values to be considered as empty when casting. Empty values are always replaced by the default value of the respective field. If the field is an array type, any empty value inside of the array will be removed. To set this option while keeping the current default, use empty_values/0 and add your additional empty values

• :force_changes - a boolean indicating whether to include values that don't alter the current data in :changes. See force_change/3 for more information, Defaults to false

• :message - a function of arity 2 that is used to create the error message when casting fails. It is called for every field that cannot be casted and receives the field name as the first argument and the error metadata as the second argument. It must return a string or nil. If a string is returned it will be used as the error message. If nil is returned the default error message will be used. The field type is given under the :type key in the metadata

Examples

iex> changeset = cast(post, params, [:title])
iex> if changeset.valid? do
...>   Repo.update!(changeset)
...> end

Passing a changeset as the first argument:

iex> changeset = cast(post, %{title: "Hello"}, [:title])
iex> new_changeset = cast(changeset, %{title: "Foo", body: "World"}, [:body])
iex> new_changeset.params
%{"title" => "Hello", "body" => "World"}

Or creating a changeset from a simple map with types:

iex> data = %{title: "hello"}
iex> types = %{title: :string}
iex> changeset = cast({data, types}, %{title: "world"}, [:title])
iex> apply_changes(changeset)
%{title: "world"}

You can use empty values (and even cast multiple times) to change what is considered an empty value:

# Using default
iex> params = %{title: "", topics: []}
iex> changeset = cast(post, params, [:title, :topics])
iex> changeset.params
%{topics: []}

# Changing default
iex> params = %{title: "", topics: []}
iex> changeset = cast(post, params, [:topics], empty_values: [[], nil])
iex> changeset.params
%{title: ""}

# Augmenting default
iex> params = %{title: "", topics: []}
iex> changeset =
...>   cast(post, params, [:topics], empty_values: [[], nil] ++ Ecto.Changeset.empty_values())
iex> changeset.params
%{}

You can define a custom error message function.

# Using field name
iex> params = %{title: 1, body: 2}
iex> custom_errors = [title: "must be a string"]
iex> msg_func = fn field, _meta -> custom_errors[field] end
iex> changeset = cast(post, params, [:title, :body], message: msg_func)
iex> changeset.errors
[
  title: {"must be a string", [type: :string, validation: :cast]},
  body: {"is_invalid", [type: :string, validation: :cast]}
]

# Using field type
iex> params = %{title: 1, body: 2}
iex> custom_errors = [string: "must be a string"]
iex> msg_func = fn _field, meta ->
...    type = meta[:type]
...    custom_errors[type]
...  end
iex> changeset = cast(post, params, [:title, :body], message: msg_func)
iex> changeset.errors
[
  title: {"must be a string", [type: :string, validation: :cast]},
  body: {"must be a string", [type: :string, validation: :cast]}
]

Composing casts

cast/4 also accepts a changeset as its first argument. In such cases, all the effects caused by the call to cast/4 (additional errors and changes) are simply added to the ones already present in the argument changeset. Parameters are merged (not deep-merged) and the ones passed to cast/4 take precedence over the ones already in the changeset.

Casts the given association with the changeset parameters.

This function should be used when working with the entire association at once (and not a single element of a many-style association) and receiving data external to the application.

cast_assoc/3 matches the records extracted from the database and compares it with the parameters received from an external source. Therefore, it is expected that the data in the changeset has explicitly preloaded the association being cast and that all of the IDs exist and are unique.

For example, imagine a user has many addresses relationship where post data is sent as follows

%{"name" => "john doe", "addresses" => [
  %{"street" => "somewhere", "country" => "brazil", "id" => 1},
  %{"street" => "elsewhere", "country" => "poland"},
]}

and then

User
|> Repo.get!(id)
|> Repo.preload(:addresses) # Only required when updating data
|> Ecto.Changeset.cast(params, [])
|> Ecto.Changeset.cast_assoc(:addresses, with: &MyApp.Address.changeset/2)

The parameters for the given association will be retrieved from changeset.params. Those parameters are expected to be a map with attributes, similar to the ones passed to cast/4. Once parameters are retrieved, cast_assoc/3 will match those parameters with the associations already in the changeset data.

Once cast_assoc/3 is called, Ecto will compare each parameter with the user's already preloaded addresses and act as follows:

• If the parameter does not contain an ID, the parameter data will be passed to MyApp.Address.changeset/2 with a new struct and become an insert operation. We only consider the ID as not given if there is no "id" key or if its value is strictly nil

• If the parameter contains an ID and there is no associated child with such ID, the parameter data will be passed to MyApp.Address.changeset/2 with a new struct and become an insert operation

• If the parameter contains an ID and there is an associated child with such ID, the parameter data will be passed to MyApp.Address.changeset/2 with the existing struct and become an update operation

• If there is an associated child with an ID and its ID is not given as parameter, the :on_replace callback for that association will be invoked (see the "On replace" section on the module documentation)

If two or more addresses have the same IDs, Ecto will consider that an error and add an error to the changeset saying that there are duplicate entries.

Every time the MyApp.Address.changeset/2 function is invoked, it must return a changeset. This changeset will always be included under changes of the parent changeset, even if there are no changes. This is done for reflection purposes, allowing developers to introspect validations and other metadata from the association. Once the parent changeset is given to an Ecto.Repo function, all entries will be inserted/updated/deleted within the same transaction.

As you see above, this function is opinionated on how it works. If you need different behaviour or if you need explicit control over the associated data, you can either use put_assoc/4 or use Ecto.Multi to encode how several database operations will happen on several schemas and changesets at once.

Custom actions

Developers are allowed to explicitly set the :action field of a changeset to instruct Ecto how to act in certain situations. Let's suppose that, if one of the associations has only empty fields, you want to ignore the entry altogether instead of showing an error. The changeset function could be written like this:

def changeset(struct, params) do
  struct
  |> cast(params, [:title, :body])
  |> validate_required([:title, :body])
  |> case do
    %{valid?: false, changes: changes} = changeset when changes == %{} ->
      # If the changeset is invalid and has no changes, it is
      # because all required fields are missing, so we ignore it.
      %{changeset | action: :ignore}
    changeset ->
      changeset
  end
end

You can also set it to delete if you want data to be deleted based on the received parameters (such as a checkbox or any other indicator).

Partial changes for many-style associations

By preloading an association using a custom query you can confine the behavior of cast_assoc/3. This opens up the possibility to work on a subset of the data, instead of all associations in the database.

Taking the initial example of users having addresses imagine those addresses are set up to belong to a country. If you want to allow users to bulk edit all addresses that belong to a single country, you can do so by changing the preload query:

query = from MyApp.Address, where: [country: ^edit_country]

User
|> Repo.get!(id)
|> Repo.preload(addresses: query)
|> Ecto.Changeset.cast(params, [])
|> Ecto.Changeset.cast_assoc(:addresses)

This will allow you to cast and update only the association for the given country. The important point for partial changes is that any addresses, which were not preloaded won't be changed.

Sorting and deleting from -many collections

In earlier examples, we passed a -many style association as a list:

%{"name" => "john doe", "addresses" => [
  %{"street" => "somewhere", "country" => "brazil", "id" => 1},
  %{"street" => "elsewhere", "country" => "poland"},
]}

However, it is also common to pass the addresses as a map, where each key is an integer representing its position:

%{"name" => "john doe", "addresses" => %{
  0 => %{"street" => "somewhere", "country" => "brazil", "id" => 1},
  1 => %{"street" => "elsewhere", "country" => "poland"}
}}

Using indexes becomes specially useful with two supporting options: :sort_param and :drop_param. These options tell the indexes should be reordered or deleted from the data. For example, if you did:

cast_embed(changeset, :addresses,
  sort_param: :addresses_sort,
  drop_param: :addresses_drop)

You can now submit this:

%{"name" => "john doe", "addresses" => %{...}, "addresses_drop" => [0]}

And now the entry with index 0 will be dropped from the params before casting. Note this requires setting the relevant :on_replace option on your associations/embeds definition.

Similar, for sorting, you could do:

%{"name" => "john doe", "addresses" => %{...}, "addresses_sort" => [1, 0]}

And that will internally sort the elements so 1 comes before 0. Note that any index not present in "addresses_sort" will come before any of the sorted indexes. If an index is not found, an empty entry is added in its place.

For embeds, this guarantees the embeds will be rewritten in the given order. However, for associations, this is not enough. You will have to add a field :position, :integer to the schema and add a with function of arity 3 to add the position to your children changeset. For example, you could implement:

defp child_changeset(child, _changes, position) do
  child
  |> change(position: position)
end

And by passing it to :with, it will be called with the final position of the item:

changeset
|> cast_assoc(:children, sort_param: ..., with: &child_changeset/3)

These parameters can be powerful in certain UIs as it allows you to decouple the sorting and replacement of the data from its representation.

More resources

You can learn more about working with associations in our documentation, including cheatsheets and practical examples. Check out:

• The docs for put_assoc/3
• The associations cheatsheet
• The Constraints and Upserts guide
• The Polymorphic associations with many to many guide

Options

• :required - if the association is a required field. For associations of cardinality one, a non-nil value satisfies this validation. For associations with many entries, a non-empty list is satisfactory.

• :required_message - the message on failure, defaults to "can't be blank"

• :invalid_message - the message on failure, defaults to "is invalid"

• :force_update_on_change - force the parent record to be updated in the repository if there is a change, defaults to true

• :with - the function to build the changeset from params. Defaults to the changeset/2 function of the associated module. It can be an anonymous function that expects two arguments: the associated struct to be cast and its parameters. It must return a changeset. For associations with cardinality :many, functions with arity 3 are accepted, and the third argument will be the position of the associated element in the list, or nil, if the association is being replaced.

• :drop_param - the parameter name which keeps a list of indexes to drop from the relation parameters

• :sort_param - the parameter name which keeps a list of indexes to sort from the relation parameters. Unknown indexes are considered to be new entries. Non-listed indexes will come before any sorted ones. See cast_assoc/3 for more information

Casts the given embed with the changeset parameters.

The parameters for the given embed will be retrieved from changeset.params. Those parameters are expected to be a map with attributes, similar to the ones passed to cast/4. Once parameters are retrieved, cast_embed/3 will match those parameters with the embeds already in the changeset record. See cast_assoc/3 for an example of working with casts and associations which would also apply for embeds.

The changeset must have been previously cast using cast/4 before this function is invoked.

Options

• :required - if the embed is a required field. For embeds of cardinality one, a non-nil value satisfies this validation. For embeds with many entries, a non-empty list is satisfactory.

• :required_message - the message on failure, defaults to "can't be blank"

• :invalid_message - the message on failure, defaults to "is invalid"

• :force_update_on_change - force the parent record to be updated in the repository if there is a change, defaults to true

• :with - the function to build the changeset from params. Defaults to the changeset/2 function of the associated module. It must be an anonymous function that expects two arguments: the embedded struct to be cast and its parameters. It must return a changeset. For embeds with cardinality :many, functions with arity 3 are accepted, and the third argument will be the position of the associated element in the list, or nil, if the embed is being replaced.

• :drop_param - the parameter name which keeps a list of indexes to drop from the relation parameters

• :sort_param - the parameter name which keeps a list of indexes to sort from the relation parameters. Unknown indexes are considered to be new entries. Non-listed indexes will come before any sorted ones. See cast_assoc/3 for more information

@spec change(
  Ecto.Schema.t() | t() | {data(), types()},
  %{required(atom()) => term()} | Keyword.t()
) ::
  t()

Wraps the given data in a changeset or adds changes to a changeset.

changes is a map or keyword where the key is an atom representing a field, association or embed and the value is a term. Note the value is directly stored in the changeset with no validation whatsoever. For this reason, this function is meant for working with data internal to the application.

When changing embeds and associations, see put_assoc/4 for a complete reference on the accepted values.

This function is useful for:

• wrapping a struct inside a changeset
• directly changing a struct without performing castings nor validations
• directly bulk-adding changes to a changeset

Changed attributes will only be added if the change does not have the same value as the field in the data.

When a changeset is passed as the first argument, the changes passed as the second argument are merged over the changes already in the changeset if they differ from the values in the struct.

When a {data, types} is passed as the first argument, a changeset is created with the given data and types and marked as valid.

See cast/4 if you'd prefer to cast and validate external parameters.

Examples

iex> changeset = change(%Post{})
%Ecto.Changeset{...}
iex> changeset.valid?
true
iex> changeset.changes
%{}

iex> changeset = change(%Post{author: "bar"}, title: "title")
iex> changeset.changes
%{title: "title"}

iex> changeset = change(%Post{title: "title"}, title: "title")
iex> changeset.changes
%{}

iex> changeset = change(changeset, %{title: "new title", body: "body"})
iex> changeset.changes.title
"new title"
iex> changeset.changes.body
"body"

@spec changed?(t(), atom(), Keyword.t()) :: boolean()

Returns true if a field was changed in a changeset.

This function can check associations and embeds, but doesn't support the :to and :from options for such fields.

Options

• :to - Check if the field was changed to a specific value
• :from - Check if the field was changed from a specific value

Examples

iex> post = %Post{title: "Foo", body: "Old"}
iex> changeset = change(post, %{title: "New title", body: "Old"})

iex> changed?(changeset, :body)
false

iex> changed?(changeset, :title)
true

iex> changed?(changeset, :title, to: "NEW TITLE")
false

Checks for a check constraint in the given field.

The check constraint works by relying on the database to check if the check constraint has been violated or not and, if so, Ecto converts it into a changeset error.

In order to use the check constraint, the first step is to define the check constraint in a migration:

create constraint("users", :age_must_be_positive, check: "age > 0")

Now that a constraint exists, when modifying users, we could annotate the changeset with a check constraint so Ecto knows how to convert it into an error message:

cast(user, params, [:age])
|> check_constraint(:age, name: :age_must_be_positive)

Now, when invoking Ecto.Repo.insert/2 or Ecto.Repo.update/2, if the age is not positive, the underlying operation will fail but Ecto will convert the database exception into a changeset error and return an {:error, changeset} tuple. Note that the error will occur only after hitting the database, so it will not be visible until all other validations pass. If the constraint fails inside a transaction, the transaction will be marked as aborted.

Options

• :message - the message in case the constraint check fails. Defaults to "is invalid"
• :name - the constraint name. By default, the constraint name is inferred from the table + field. If this option is given, the field argument only indicates the field the error will be added to. May be required explicitly for complex cases
• :match - how the changeset constraint name is matched against the repo constraint, may be :exact, :suffix or :prefix. Defaults to :exact. :suffix matches any repo constraint which ends_with? :name to this changeset constraint. :prefix matches any repo constraint which starts_with? :name to this changeset constraint.

@spec constraints(t()) :: [constraint()]

Returns all constraints in a changeset.

A constraint is a map with the following fields:

• :type - the type of the constraint that will be checked in the database, such as :check, :unique, etc
• :constraint - the database constraint name as a string or Regex. The constraint at the database level will be checked against this according to :match type
• :match - the type of match Ecto will perform on a violated constraint against the :constraint value. It is :exact, :suffix or :prefix
• :field - the field a violated constraint will apply the error to
• :error_message - the error message in case of violated constraints
• :error_type - the type of error that identifies the error message

@spec delete_change(t(), atom()) :: t()

Deletes a change with the given key.

Examples

iex> changeset = change(%Post{}, %{title: "foo"})
iex> changeset = delete_change(changeset, :title)
iex> get_change(changeset, :title)
nil

@spec empty_values() :: [empty_value()]

Returns the default empty values used by Ecto.Changeset.

By default, Ecto marks a field as empty if it is a string made only of whitespace characters. If you want to provide your additional empty values on top of the default, such as an empty list, you can write:

@empty_values [[]] ++ Ecto.Changeset.empty_values()

Then, you can pass empty_values: @empty_values on cast/3.

See also the Empty values section for more information.

Checks for an exclusion constraint in the given field.

The exclusion constraint works by relying on the database to check if the exclusion constraint has been violated or not and, if so, Ecto converts it into a changeset error.

Options

• :message - the message in case the constraint check fails, defaults to "violates an exclusion constraint"
• :name - the constraint name. By default, the constraint name is inferred from the table + field. If this option is given, the field argument only indicates the field the error will be added to. May be required explicitly for complex cases
• :match - how the changeset constraint name is matched against the repo constraint, may be :exact, :suffix or :prefix. Defaults to :exact. :suffix matches any repo constraint which ends_with? :name to this changeset constraint. :prefix matches any repo constraint which starts_with? :name to this changeset constraint.

@spec fetch_change(t(), atom()) :: {:ok, term()} | :error

Fetches a change from the given changeset.

This function only looks at the :changes field of the given changeset and returns {:ok, value} if the change is present or :error if it's not.

Examples

iex> changeset = change(%Post{body: "foo"}, %{title: "bar"})
iex> fetch_change(changeset, :title)
{:ok, "bar"}
iex> fetch_change(changeset, :body)
:error

@spec fetch_change!(t(), atom()) :: term()

Same as fetch_change/2 but returns the value or raises if the given key was not found.

Examples

iex> changeset = change(%Post{body: "foo"}, %{title: "bar"})
iex> fetch_change!(changeset, :title)
"bar"
iex> fetch_change!(changeset, :body)
** (KeyError) key :body not found in: %{title: "bar"}

@spec fetch_field(t(), atom()) :: {:changes, term()} | {:data, term()} | :error

Fetches the given field from changes or from the data.

While fetch_change/2 only looks at the current changes to retrieve a value, this function looks at the changes and then falls back on the data, finally returning :error if no value is available.

For relations, these functions will return the changeset original data with changes applied. To retrieve raw changesets, please use fetch_change/2.

Examples

iex> post = %Post{title: "Foo", body: "Bar baz bong"}
iex> changeset = change(post, %{title: "New title"})
iex> fetch_field(changeset, :title)
{:changes, "New title"}
iex> fetch_field(changeset, :body)
{:data, "Bar baz bong"}
iex> fetch_field(changeset, :not_a_field)
:error

@spec fetch_field!(t(), atom()) :: term()

Same as fetch_field/2 but returns the value or raises if the given key was not found.

Examples

iex> post = %Post{title: "Foo", body: "Bar baz bong"}
iex> changeset = change(post, %{title: "New title"})
iex> fetch_field!(changeset, :title)
"New title"
iex> fetch_field!(changeset, :other)
** (KeyError) key :other not found in: %Post{...}

@spec field_missing?(t(), atom()) :: boolean()

Determines whether a field is missing in a changeset.

The field passed into this function will have its presence evaluated according to the same rules as validate_required/3.

This is useful when performing complex validations that are not possible with validate_required/3. For example, evaluating whether at least one field from a list is present or evaluating that exactly one field from a list is present.

Examples

iex> changeset = cast(%Post{}, %{color: "Red"}, [:color])
iex> missing_fields = Enum.filter([:title, :body], &field_missing?(changeset, &1))
iex> changeset =
...>   case missing_fields do
...>     [_, _] -> add_error(changeset, :title, "at least one of `:title` or `:body` must be present")
...>     _ -> changeset
...>   end
...> changeset.errors
[title: {"at least one of `:title` or `:body` must be present", []}]

@spec force_change(t(), atom(), term()) :: t()

Forces a change on the given key with value.

If the change is already present, it is overridden with the new value. If the value is later modified via put_change/3 and update_change/3, reverting back to its original value, the change will be reverted unless force_change/3 is called once again.

Examples

iex> changeset = change(%Post{author: "bar"}, %{title: "foo"})
iex> changeset = force_change(changeset, :title, "bar")
iex> changeset.changes
%{title: "bar"}

iex> changeset = force_change(changeset, :author, "bar")
iex> changeset.changes
%{title: "bar", author: "bar"}

@spec foreign_key_constraint(t(), atom(), Keyword.t()) :: t()

Checks for foreign key constraint in the given field.

The foreign key constraint works by relying on the database to check if the associated data exists or not. This is useful to guarantee that a child will only be created if the parent exists in the database too.

In order to use the foreign key constraint the first step is to define the foreign key in a migration. This is often done with references. For example, imagine you are creating a comments table that belongs to posts. One would have:

create table(:comments) do
  add :post_id, references(:posts)
end

By default, Ecto will generate a foreign key constraint with name "comments_post_id_fkey" (the name is configurable).

Now that a constraint exists, when creating comments, we could annotate the changeset with foreign key constraint so Ecto knows how to convert it into an error message:

cast(comment, params, [:post_id])
|> foreign_key_constraint(:post_id)

Now, when invoking Ecto.Repo.insert/2 or Ecto.Repo.update/2, if the associated post does not exist, the underlying operation will fail but Ecto will convert the database exception into a changeset error and return an {:error, changeset} tuple. Note that the error will occur only after hitting the database, so it will not be visible until all other validations pass. If the constraint fails inside a transaction, the transaction will be marked as aborted.

Options

• :message - the message in case the constraint check fails, defaults to "does not exist"
• :name - the constraint name. By default, the constraint name is inferred from the table + field. If this option is given, the field argument only indicates the field the error will be added to. May be required explicitly for complex cases
• :match - how the changeset constraint name is matched against the repo constraint, may be :exact, :suffix or :prefix. Defaults to :exact. :suffix matches any repo constraint which ends_with? :name to this changeset constraint. :prefix matches any repo constraint which starts_with? :name to this changeset constraint.

Gets the association entry or entries from changes or from the data.

Returned data is normalized to changesets by default. Pass the :struct flag to retrieve the data as structs with changes applied, similar to get_field/2.

Examples

iex> %Author{posts: [%Post{id: 1, title: "hello"}]}
...> |> change()
...> |> get_assoc(:posts)
[%Ecto.Changeset{data: %Post{id: 1, title: "hello"}, changes: %{}}]

iex> %Author{posts: [%Post{id: 1, title: "hello"}]}
...> |> cast(%{posts: [%{id: 1, title: "world"}]}, [])
...> |> cast_assoc(:posts)
...> |> get_assoc(:posts, :changeset)
[%Ecto.Changeset{data: %Post{id: 1, title: "hello"}, changes: %{title: "world"}}]

iex> %Author{posts: [%Post{id: 1, title: "hello"}]}
...> |> cast(%{posts: [%{id: 1, title: "world"}]}, [])
...> |> cast_assoc(:posts)
...> |> get_assoc(:posts, :struct)
[%Post{id: 1, title: "world"}]

@spec get_change(t(), atom(), term()) :: term()

Gets a change or returns a default value.

For associations and embeds, this function always returns nil, a changeset, or a list of changesets.

Examples

iex> changeset = change(%Post{body: "foo"}, %{title: "bar"})
iex> get_change(changeset, :title)
"bar"
iex> get_change(changeset, :body)
nil

Gets the embedded entry or entries from changes or from the data.

Returned data is normalized to changesets by default. Pass the :struct flag to retrieve the data as structs with changes applied, similar to get_field/2.

Examples

iex> %Post{comments: [%Comment{id: 1, body: "hello"}]}
...> |> change()
...> |> get_embed(:comments)
[%Ecto.Changeset{data: %Comment{id: 1, body: "hello"}, changes: %{}}]

iex> %Post{comments: [%Comment{id: 1, body: "hello"}]}
...> |> cast(%{comments: [%{id: 1, body: "world"}]}, [])
...> |> cast_embed(:comments)
...> |> get_embed(:comments, :changeset)
[%Ecto.Changeset{data: %Comment{id: 1, body: "hello"}, changes: %{body: "world"}}]

iex> %Post{comments: [%Comment{id: 1, body: "hello"}]}
...> |> cast(%{comments: [%{id: 1, body: "world"}]}, [])
...> |> cast_embed(:comments)
...> |> get_embed(:comments, :struct)
[%Comment{id: 1, body: "world"}]

@spec get_field(t(), atom(), term()) :: term()

Gets a field from changes or from the data.

While get_change/3 only looks at the current changes to retrieve a value, this function looks at the changes and then falls back on the data, finally returning default if no value is available.

For associations and embeds, this function always returns nil, a struct, or a list of structs. In case of changes, the changeset data will have all data applies. This guarantees a consistent result regardless if changes have been applied or not. Use get_change/2 or get_assoc/3/get_embed/3 if you want to retrieve the relations as changesets or if you want more fine-grained control.

iex> post = %Post{title: "A title", body: "My body is a cage"}
iex> changeset = change(post, %{title: "A new title"})
iex> get_field(changeset, :title)
"A new title"
iex> get_field(changeset, :not_a_field, "Told you, not a field!")
"Told you, not a field!"

@spec merge(t(), t()) :: t()

Merges two changesets.

This function merges two changesets provided they have been applied to the same data (their :data field is equal); if the data differs, an ArgumentError exception is raised. If one of the changesets has a :repo field which is not nil, then the value of that field is used as the :repo field of the resulting changeset; if both changesets have a non-nil and different :repo field, an ArgumentError exception is raised.

The other fields are merged with the following criteria:

• params - params are merged (not deep-merged) giving precedence to the params of changeset2 in case of a conflict. If both changesets have their :params fields set to nil, the resulting changeset will have its params set to nil too.
• changes - changes are merged giving precedence to the changeset2 changes.
• errors and validations - they are simply concatenated.
• required - required fields are merged; all the fields that appear in the required list of both changesets are moved to the required list of the resulting changeset.

Examples

iex> changeset1 = cast(%Post{}, %{title: "Title"}, [:title])
iex> changeset2 = cast(%Post{}, %{title: "New title", body: "Body"}, [:title, :body])
iex> changeset = merge(changeset1, changeset2)
iex> changeset.changes
%{body: "Body", title: "New title"}

iex> changeset1 = cast(%Post{body: "Body"}, %{title: "Title"}, [:title])
iex> changeset2 = cast(%Post{}, %{title: "New title"}, [:title])
iex> merge(changeset1, changeset2)
** (ArgumentError) different :data when merging changesets

@spec no_assoc_constraint(t(), atom(), Keyword.t()) :: t()

Checks the associated field does not exist.

This is similar to foreign_key_constraint/3 except that the field is inferred from the association definition. This is useful to guarantee that parent can only be deleted (or have its primary key changed) if no child exists in the database. Therefore, it only applies to has_* associations.

As the name says, a constraint is required in the database for this function to work. Such constraint is often added as a reference to the child table:

create table(:comments) do
  add :post_id, references(:posts)
end

Now, when deleting the post, it is possible to forbid any post to be deleted if they still have comments attached to it:

post
|> Ecto.Changeset.change
|> Ecto.Changeset.no_assoc_constraint(:comments)
|> Repo.delete

Options

• :message - the message in case the constraint check fails, defaults to "is still associated with this entry" (for has_one) and "are still associated with this entry" (for has_many)
• :name - the constraint name. By default, the constraint name is inferred from the table + field. If this option is given, the field argument only indicates the field the error will be added to. May be required explicitly for complex cases
• :match - how the changeset constraint name is matched against the repo constraint, may be :exact, :suffix or :prefix. Defaults to :exact. :suffix matches any repo constraint which ends_with? :name to this changeset constraint. :prefix matches any repo constraint which starts_with? :name to this changeset constraint.

@spec optimistic_lock(Ecto.Schema.t() | t(), atom(), (term() -> term())) :: t()

Applies optimistic locking to the changeset.

Optimistic locking (or optimistic concurrency control) is a technique that allows concurrent edits on a single record. While pessimistic locking works by locking a resource for an entire transaction, optimistic locking only checks if the resource changed before updating it.

This is done by regularly fetching the record from the database, then checking whether another user has made changes to the record only when updating the record. This behaviour is ideal in situations where the chances of concurrent updates to the same record are low; if they're not, pessimistic locking or other concurrency patterns may be more suited.

Usage

Optimistic locking works by keeping a "version" counter for each record; this counter gets incremented each time a modification is made to a record. Hence, in order to use optimistic locking, a field must exist in your schema for versioning purpose. Such field is usually an integer but other types are supported.

Examples

Assuming we have a Post schema (stored in the posts table), the first step is to add a version column to the posts table:

alter table(:posts) do
  add :lock_version, :integer, default: 1
end

The column name is arbitrary and doesn't need to be :lock_version. Now add a field to the schema too:

defmodule Post do
  use Ecto.Schema

  schema "posts" do
    field :title, :string
    field :lock_version, :integer, default: 1
  end

  def changeset(:update, struct, params \\ %{}) do
    struct
    |> Ecto.Changeset.cast(params, [:title])
    |> Ecto.Changeset.optimistic_lock(:lock_version)
  end
end

Now let's take optimistic locking for a spin:

iex> post = Repo.insert!(%Post{title: "foo"})
%Post{id: 1, title: "foo", lock_version: 1}
iex> valid_change = Post.changeset(:update, post, %{title: "bar"})
iex> stale_change = Post.changeset(:update, post, %{title: "baz"})
iex> Repo.update!(valid_change)
%Post{id: 1, title: "bar", lock_version: 2}
iex> Repo.update!(stale_change)
** (Ecto.StaleEntryError) attempted to update a stale entry:

%Post{id: 1, title: "baz", lock_version: 1}

When a conflict happens (a record which has been previously fetched is being updated, but that same record has been modified since it was fetched), an Ecto.StaleEntryError exception is raised.

Optimistic locking also works with delete operations. Just call the optimistic_lock/3 function with the data before delete:

iex> changeset = Ecto.Changeset.optimistic_lock(post, :lock_version)
iex> Repo.delete(changeset)

optimistic_lock/3 by default assumes the field being used as a lock is an integer. If you want to use another type, you need to pass the third argument customizing how the next value is generated:

iex> Ecto.Changeset.optimistic_lock(post, :lock_uuid, fn _ -> Ecto.UUID.generate end)

@spec prepare_changes(t(), (t() -> t())) :: t()

Provides a function executed by the repository on insert/update/delete.

If the changeset given to the repository is valid, the function given to prepare_changes/2 will be called with the changeset and must return a changeset, allowing developers to do final adjustments to the changeset or to issue data consistency commands. The repository itself can be accessed inside the function under the repo field in the changeset. If the changeset given to the repository is invalid, the function will not be invoked.

The given function is guaranteed to run inside the same transaction as the changeset operation for databases that do support transactions.

Example

A common use case is updating a counter cache, in this case updating a post's comment count when a comment is created:

def create_comment(comment, params) do
  comment
  |> cast(params, [:body, :post_id])
  |> prepare_changes(fn changeset ->
       if post_id = get_change(changeset, :post_id) do
         query = from Post, where: [id: ^post_id]
         changeset.repo.update_all(query, inc: [comment_count: 1])
       end
       changeset
     end)
end

We retrieve the repo from the comment changeset itself and use update_all to update the counter cache in one query. Finally, the original changeset must be returned.

Puts the given association entry or entries as a change in the changeset.

This function is used to work with associations as a whole. For example, if a Post has many Comments, it allows you to add, remove or change all comments at once. If your goal is to simply add a new comment to a post, then it is preferred to do so manually, as we will describe later in the "Example: Adding a comment to a post" section.

This function requires the associated data to have been preloaded, except when the parent changeset has been newly built and not yet persisted. Missing data will invoke the :on_replace behaviour defined on the association.

For associations with cardinality one, nil can be used to remove the existing entry. For associations with many entries, an empty list may be given instead.

If the association has no changes, it will be skipped. If the association is invalid, the changeset will be marked as invalid. If the given value is not any of values below, it will raise.

The associated data may be given in different formats:

• a map or a keyword list representing changes to be applied to the associated data. A map or keyword list can be given to update the associated data as long as they have matching primary keys. For example, put_assoc(changeset, :comments, [%{id: 1, title: "changed"}]) will locate the comment with :id of 1 and update its title. If no comment with such id exists, one is created on the fly. Since only a single comment was given, any other associated comment will be replaced. On all cases, it is expected the keys to be atoms. Opposite to cast_assoc and embed_assoc, the given map (or struct) is not validated in any way and will be inserted as is. This API is mostly used in scripts and tests, to make it straight- forward to create schemas with associations at once, such as:

  Ecto.Changeset.change(
    %Post{},
    title: "foo",
    comments: [
      %{body: "first"},
      %{body: "second"}
    ]
  )

• changesets - when changesets are given, they are treated as the canonical data and the associated data currently stored in the association is either updated or replaced. For example, if you call put_assoc(post_changeset, :comments, [list_of_comments_changesets]), all comments with matching IDs will be updated according to the changesets. New comments or comments not associated to any post will be correctly associated. Currently associated comments that do not have a matching ID in the list of changesets will act according to the :on_replace association configuration (you can chose to raise, ignore the operation, update or delete them). If there are changes in any of the changesets, they will be persisted too.

• structs - when structs are given, they are treated as the canonical data and the associated data currently stored in the association is replaced. For example, if you call put_assoc(post_changeset, :comments, [list_of_comments_structs]), all comments with matching IDs will be replaced by the new structs. New comments or comments not associated to any post will be correctly associated. Currently associated comments that do not have a matching ID in the list of changesets will act according to the :on_replace association configuration (you can chose to raise, ignore the operation, update or delete them). Different to passing changesets, structs are not change tracked in any fashion. In other words, if you change a comment struct and give it to put_assoc/4, the updates in the struct won't be persisted. You must use changesets instead. put_assoc/4 with structs only takes care of guaranteeing that the comments and the parent data are associated. This is extremely useful when associating existing data, as we will see in the "Example: Adding tags to a post" section.

Once the parent changeset is given to an Ecto.Repo function, all entries will be inserted/updated/deleted within the same transaction.

If you need different behaviour or explicit control over how this function behaves, you can drop it altogether and use Ecto.Multi to encode how several database operations will happen on several schemas and changesets at once.

Example: Adding a comment to a post

Imagine a relationship where Post has many comments and you want to add a new comment to an existing post. While it is possible to use put_assoc/4 for this, it would be unnecessarily complex. Let's see an example.

First, let's fetch the post with all existing comments:

post = Post |> Repo.get!(1) |> Repo.preload(:comments)

The following approach is wrong:

post
|> Ecto.Changeset.change()
|> Ecto.Changeset.put_assoc(:comments, [%Comment{body: "bad example!"}])
|> Repo.update!()

The reason why the example above is wrong is because put_assoc/4 always works with the full data. So the example above will effectively erase all previous comments and only keep the comment you are currently adding. Instead, you could try:

post
|> Ecto.Changeset.change()
|> Ecto.Changeset.put_assoc(:comments, [%Comment{body: "so-so example!"} | post.comments])
|> Repo.update!()

In this example, we prepend the new comment to the list of existing comments. Ecto will diff the list of comments currently in post with the list of comments given, and correctly insert the new comment to the database. Note, however, Ecto is doing a lot of work just to figure out something we knew since the beginning, which is that there is only one new comment.

In cases like above, when you want to work only on a single entry, it is much easier to simply work on the associated directly. For example, we could instead set the post association in the comment:

%Comment{body: "better example"}
|> Ecto.Changeset.change()
|> Ecto.Changeset.put_assoc(:post, post)
|> Repo.insert!()

Alternatively, we can make sure that when we create a comment, it is already associated to the post:

Ecto.build_assoc(post, :comments)
|> Ecto.Changeset.change(body: "great example!")
|> Repo.insert!()

Or we can simply set the post_id in the comment itself:

%Comment{body: "better example", post_id: post.id}
|> Repo.insert!()

In other words, when you find yourself wanting to work only with a subset of the data, then using put_assoc/4 is most likely unnecessary. Instead, you want to work on the other side of the association.

Let's see an example where using put_assoc/4 is a good fit.

Example: Adding tags to a post

Imagine you are receiving a set of tags you want to associate to a post. Let's imagine that those tags exist upfront and are all persisted to the database. Imagine we get the data in this format:

params = %{"title" => "new post", "tags" => ["learner"]}

Now, since the tags already exist, we will bring all of them from the database and put them directly in the post:

tags = Repo.all(from t in Tag, where: t.name in ^params["tags"])

post
|> Repo.preload(:tags)
|> Ecto.Changeset.cast(params, [:title]) # No need to allow :tags as we put them directly
|> Ecto.Changeset.put_assoc(:tags, tags) # Explicitly set the tags

Since in this case we always require the user to pass all tags directly, using put_assoc/4 is a great fit. It will automatically remove any tag not given and properly associate all of the given tags with the post.

Furthermore, since the tag information is given as structs read directly from the database, Ecto will treat the data as correct and only do the minimum necessary to guarantee that posts and tags are associated, without trying to update or diff any of the fields in the tag struct.

Although it accepts an opts argument, there are no options currently supported by put_assoc/4.

More resources

You can learn more about working with associations in our documentation, including cheatsheets and practical examples. Check out:

• The docs for cast_assoc/3
• The associations cheatsheet
• The Constraints and Upserts guide
• The Polymorphic associations with many to many guide

@spec put_change(t(), atom(), term()) :: t()

Puts a change on the given key with value.

key is an atom that represents any field, embed or association in the changeset. Note the value is directly stored in the changeset with no validation whatsoever. For this reason, this function is meant for working with data internal to the application.

If the change is already present, it is overridden with the new value. If the change has the same value as in the changeset data, no changes are added (and any existing changes are removed).

When changing embeds and associations, see put_assoc/4 for a complete reference on the accepted values.

Examples

iex> changeset = change(%Post{}, %{title: "foo"})
iex> changeset = put_change(changeset, :title, "bar")
iex> changeset.changes
%{title: "bar"}

iex> changeset = change(%Post{title: "foo"})
iex> changeset = put_change(changeset, :title, "foo")
iex> changeset.changes
%{}

Puts the given embed entry or entries as a change in the changeset.

This function is used to work with embeds as a whole. For embeds with cardinality one, nil can be used to remove the existing entry. For embeds with many entries, an empty list may be given instead.

If the embed has no changes, it will be skipped. If the embed is invalid, the changeset will be marked as invalid.

The list of supported values and their behaviour is described in put_assoc/4. If the given value is not any of values listed there, it will raise.

Although this function accepts an opts argument, there are no options currently supported by put_embed/4.

@spec traverse_errors(
  t(),
  (error() -> String.t()) | (t(), atom(), error() -> String.t())
) ::
  traverse_result()

Traverses changeset errors and applies the given function to error messages.

This function is particularly useful when associations and embeds are cast in the changeset as it will traverse all associations and embeds and place all errors in a series of nested maps.

A changeset is supplied along with a function to apply to each error message as the changeset is traversed. The error message function receives an error tuple {msg, opts}, for example:

{"should be at least %{count} characters", [count: 3, validation: :length, min: 3]}

Examples

iex> traverse_errors(changeset, fn {msg, opts} ->
...>   Regex.replace(~r"%{(\w+)}", msg, fn _, key ->
...>     opts |> Keyword.get(String.to_existing_atom(key), key) |> to_string()
...>   end)
...> end)
%{title: ["should be at least 3 characters"]}

Optionally function can accept three arguments: changeset, field and error tuple {msg, opts}. It is useful whenever you want to extract validations rules from changeset.validations to build detailed error description.

@spec traverse_validations(
  t(),
  (error() -> String.t()) | (t(), atom(), error() -> String.t())
) :: traverse_result()

Traverses changeset validations and applies the given function to validations.

This behaves the same as traverse_errors/2, but operates on changeset validations instead of errors.

Examples

iex> traverse_validations(changeset, &(&1))
%{title: [format: ~r/pattern/, length: [min: 1, max: 20]]}

iex> traverse_validations(changeset, fn
...>   {:length, opts} -> {:length, "#{Keyword.get(opts, :min, 0)}-#{Keyword.get(opts, :max, 32)}"}
...>   {:format, %Regex{source: source}} -> {:format, "/#{source}/"}
...>   {other, opts} -> {other, inspect(opts)}
...> end)
%{title: [format: "/pattern/", length: "1-20"]}

@spec unique_constraint(t(), atom() | [atom(), ...], Keyword.t()) :: t()

Checks for a unique constraint in the given field or list of fields.

The unique constraint works by relying on the database to check if the unique constraint has been violated or not and, if so, Ecto converts it into a changeset error.

In order to use the uniqueness constraint, the first step is to define the unique index in a migration:

create unique_index(:users, [:email])

Now that a constraint exists, when modifying users, we could annotate the changeset with a unique constraint so Ecto knows how to convert it into an error message:

cast(user, params, [:email])
|> unique_constraint(:email)

Now, when invoking Ecto.Repo.insert/2 or Ecto.Repo.update/2, if the email already exists, the underlying operation will fail but Ecto will convert the database exception into a changeset error and return an {:error, changeset} tuple. Note that the error will occur only after hitting the database, so it will not be visible until all other validations pass. If the constraint fails inside a transaction, the transaction will be marked as aborted.

Options

• :message - the message in case the constraint check fails, defaults to "has already been taken"

• :name - the constraint name. By default, the constraint name is inferred from the table + field. If this option is given, the field argument only indicates the field the error will be added to. May be required explicitly for complex cases

• :match - how the changeset constraint name is matched against the repo constraint, may be :exact, :suffix or :prefix. Defaults to :exact. :suffix matches any repo constraint which ends_with? :name to this changeset constraint. :prefix matches any repo constraint which starts_with? :name to this changeset constraint.

• :error_key - the key to which changeset error will be added when check fails, defaults to the first field name of the given list of fields.

Complex constraints

Because the constraint logic is in the database, we can leverage all the database functionality when defining them. For example, let's suppose the e-mails are scoped by company id:

# In migration
create unique_index(:users, [:email, :company_id])

# In the changeset function
cast(user, params, [:email])
|> unique_constraint([:email, :company_id])

The first field name, :email in this case, will be used as the error key to the changeset errors keyword list. For example, the above unique_constraint/3 would generate something like:

Repo.insert!(%User{email: "john@elixir.org", company_id: 1})
changeset = User.changeset(%User{}, %{email: "john@elixir.org", company_id: 1})
{:error, changeset} = Repo.insert(changeset)
changeset.errors #=> [email: {"has already been taken", []}]

In complex cases, instead of relying on name inference, it may be best to set the constraint name explicitly:

# In the migration
create unique_index(:users, [:email, :company_id], name: :users_email_company_id_index)

# In the changeset function
cast(user, params, [:email])
|> unique_constraint(:email, name: :users_email_company_id_index)

Partitioning

If your table is partitioned, then your unique index might look different per partition, e.g. Postgres adds p<number> to the middle of your key, like:

users_p0_email_key
users_p1_email_key
...
users_p99_email_key

In this case you can use the name and suffix options together to match on these dynamic indexes, like:

cast(user, params, [:email])
|> unique_constraint(:email, name: :email_key, match: :suffix)

There are cases where the index has a number added both for table name and index name, generating an index name such as:

user_p0_email_idx2
user_p1_email_idx3
...
user_p99_email_idx101

In that case, a Regex can be used to match:

cast(user, params, [:email])
|> unique_constraint(:email, name: ~r/user_p+_email_idx+/)

Case sensitivity

Unfortunately, different databases provide different guarantees when it comes to case-sensitiveness. For example, in MySQL, comparisons are case-insensitive by default. In Postgres, users can define case insensitive column by using the :citext type/extension. In your migration:

execute "CREATE EXTENSION IF NOT EXISTS citext"
create table(:users) do
  ...
  add :email, :citext
  ...
end

If for some reason your database does not support case insensitive columns, you can explicitly downcase values before inserting/updating them:

cast(data, params, [:email])
|> update_change(:email, &String.downcase/1)
|> unique_constraint(:email)

@spec unsafe_validate_unique(t(), atom() | [atom(), ...], Ecto.Repo.t(), Keyword.t()) ::
  t()

Validates that no existing record with a different primary key has the same values for these fields.

This function exists to provide quick feedback to users of your application. It should not be relied on for any data guarantee as it has race conditions and is inherently unsafe. For example, if this check happens twice in the same time interval (because the user submitted a form twice), both checks may pass and you may end-up with duplicate entries in the database. Therefore, a unique_constraint/3 should also be used to ensure your data won't get corrupted.

However, because constraints are only checked if all validations succeed, this function can be used as an early check to provide early feedback to users, since most conflicting data will have been inserted prior to the current validation phase.

When applying this validation to a schemas loaded from the database this check will exclude rows having the same primary key as set on the changeset, as those are supposed to be overwritten anyways.

Options

• :message - the message in case the constraint check fails, defaults to "has already been taken".

• :error_key - the key to which changeset error will be added when check fails, defaults to the first field name of the given list of fields.

• :prefix - the prefix to run the query on (such as the schema path in Postgres or the database in MySQL). See Ecto.Repo documentation for more information.

• :nulls_distinct - a boolean controlling whether different null values are considered distinct (not equal). If false, nil values will have their uniqueness checked. Otherwise, the check will not be performed. This is only meaningful when paired with a unique index that treats nulls as equal, such as Postgres 15's NULLS NOT DISTINCT option. Defaults to true

• :repo_opts - the options to pass to the Ecto.Repo call.

• :query - the base query to use for the check. Defaults to the schema of the changeset. If the primary key is set, a clause will be added to exclude the changeset row itself from the check.

Examples

unsafe_validate_unique(changeset, :city_name, repo)
unsafe_validate_unique(changeset, [:city_name, :state_name], repo)
unsafe_validate_unique(changeset, [:city_name, :state_name], repo, message: "city must be unique within state")
unsafe_validate_unique(changeset, [:city_name, :state_name], repo, prefix: "public")
unsafe_validate_unique(changeset, [:city_name, :state_name], repo, query: from(c in City, where: is_nil(c.deleted_at)))

@spec update_change(t(), atom(), (term() -> term())) :: t()

Updates a change.

The given function is invoked with the change value only if there is a change for key. Once the function is invoked, it behaves as put_changed/3.

Note that the value of the change can still be nil (unless the field was marked as required on validate_required/3).

Examples

iex> changeset = change(%Post{}, %{impressions: 1})
iex> changeset = update_change(changeset, :impressions, &(&1 + 1))
iex> changeset.changes.impressions
2