Ecto v3.3.4 Ecto.Multi View Source

Ecto.Multi is a data structure for grouping multiple Repo operations.

Ecto.Multi makes it possible to pack operations that should be performed in a single database transaction and gives a way to introspect the queued operations without actually performing them. Each operation is given a name that is unique and will identify its result in case of success or failure.

All operations will be executed in the order they were added.

The Ecto.Multi structure should be considered opaque. You can use %Ecto.Multi{} to pattern match the type, but accessing fields or directly modifying them is not advised.

Ecto.Multi.to_list/1 returns a canonical representation of the structure that can be used for introspection.

Changesets

If multi contains operations that accept changesets (like insert/4, update/4 or delete/4) they will be checked before starting the transaction. If any changeset has errors, the transaction won't even be started and the error will be immediately returned.

Note: insert/4, update/4, insert_or_update/4, and delete/4 variants that accept a function are not performing such checks since the functions are executed after the transaction has started.

Run

Multi allows you to run arbitrary functions as part of your transaction via run/3 and run/5. This is especially useful when an operation depends on the value of a previous operation. For this reason, the function given as a callback to run/3 and run/5 will receive the repo as the first argument, and all changes performed by the multi so far as a map for the second argument.

The function given to run must return {:ok, value} or {:error, value} as its result. Returning an error will abort any further operations and make the whole multi fail.

Example

Let's look at an example definition and usage. The use case we'll be looking into is resetting a password. We need to update the account with proper information, log the request and remove all current sessions:

defmodule PasswordManager do
  alias Ecto.Multi

  def reset(account, params) do
    Multi.new()
    |> Multi.update(:account, Account.password_reset_changeset(account, params))
    |> Multi.insert(:log, Log.password_reset_changeset(account, params))
    |> Multi.delete_all(:sessions, Ecto.assoc(account, :sessions))
  end
end

We can later execute it in the integration layer using Repo:

Repo.transaction(PasswordManager.reset(account, params))

By pattern matching on the result we can differentiate different conditions:

case result do
  {:ok, %{account: account, log: log, sessions: sessions}} ->
    # Operation was successful, we can access results (exactly the same
    # we would get from running corresponding Repo functions) under keys
    # we used for naming the operations.
  {:error, failed_operation, failed_value, changes_so_far} ->
    # One of the operations failed. We can access the operation's failure
    # value (like changeset for operations on changesets) to prepare a
    # proper response. We also get access to the results of any operations
    # that succeeded before the indicated operation failed. However, any
    # successful operations would have been rolled back.
end

We can also easily unit test our transaction without actually running it. Since changesets can use in-memory-data, we can use an account that is constructed in memory as well (without persisting it to the database):

test "dry run password reset" do
  account = %Account{password: "letmein"}
  multi = PasswordManager.reset(account, params)

  assert [
    {:account, {:update, account_changeset, []}},
    {:log, {:insert, log_changeset, []}},
    {:sessions, {:delete_all, query, []}}
  ] = Ecto.Multi.to_list(multi)

  # We can introspect changesets and query to see if everything
  # is as expected, for example:
  assert account_changeset.valid?
  assert log_changeset.valid?
  assert inspect(query) == "#Ecto.Query<from a in Session>"
end

The name of each operation does not have to be an atom. This can be particularly useful when you wish to update a collection of changesets at once, and track their errors individually:

accounts = [%Account{id: 1}, %Account{id: 2}]

Enum.reduce(accounts, Multi.new(), fn account, multi ->
  Multi.update(
    multi,
    {:account, account.id},
    Account.password_reset_changeset(account, params)
  )
end)

Link to this section Summary

Types

changes()

fun(result)

merge()

name()

run()

t()

Functions

append(lhs, rhs)

Appends the second multi to the first one.

delete(multi, name, changeset_or_struct_fun, opts \\ [])

Adds a delete operation to the multi.

delete_all(multi, name, queryable, opts \\ [])

Adds a delete_all operation to the multi.

error(multi, name, value)

Causes the multi to fail with the given value.

insert(multi, name, changeset_or_struct_or_fun, opts \\ [])

Adds an insert operation to the multi.

insert_all(multi, name, schema_or_source, entries, opts \\ [])

Adds an insert_all operation to the multi.

insert_or_update(multi, name, changeset, opts \\ [])

Inserts or updates a changeset depending on whether the changeset was persisted or not.

merge(multi, merge)

Merges a multi returned dynamically by an anonymous function.

merge(multi, mod, fun, args)

Merges a multi returned dynamically by calling module and function with args.

new()

Returns an empty Ecto.Multi struct.

prepend(lhs, rhs)

Prepends the second multi to the first one.

run(multi, name, run)

Adds a function to run as part of the multi.

run(multi, name, mod, fun, args)

Adds a function to run as part of the multi.

to_list(multi)

Returns the list of operations stored in multi.

update(multi, name, changeset_or_fun, opts \\ [])

Adds an update operation to the multi.

update_all(multi, name, queryable, updates, opts \\ [])

Adds an update_all operation to the multi.

Link to this section Types

changes()

changes() :: map()

fun(result)

fun(result) :: (changes() -> result)

merge()

merge() :: (changes() -> t()) | {module(), atom(), [any()]}

name()

name() :: any()

run()

run() ::
  (Ecto.Repo.t(), changes() -> {:ok | :error, any()})
  | {module(), atom(), [any()]}

t()

t() :: %Ecto.Multi{names: names(), operations: operations()}

Link to this section Functions

append(lhs, rhs)

append(t(), t()) :: t()

Appends the second multi to the first one.

All names must be unique between both structures.

Example

iex> lhs = Ecto.Multi.new() |> Ecto.Multi.run(:left, fn _, changes -> {:ok, changes} end)
iex> rhs = Ecto.Multi.new() |> Ecto.Multi.run(:right, fn _, changes -> {:error, changes} end)
iex> Ecto.Multi.append(lhs, rhs) |> Ecto.Multi.to_list |> Keyword.keys
[:left, :right]

delete(multi, name, changeset_or_struct_fun, opts \\ [])

delete(
  t(),
  name(),
  Ecto.Changeset.t()
  | Ecto.Schema.t()
  | fun(Ecto.Changeset.t() | Ecto.Schema.t()),
  Keyword.t()
) :: t()

Adds a delete operation to the multi.

Accepts the same arguments and options as Ecto.Repo.delete/2 does.

Example

post = MyApp.Repo.get!(Post, 1)
Ecto.Multi.new()
|> Ecto.Multi.delete(:delete, post)
|> MyApp.Repo.transaction()

Ecto.Multi.new()
|> Ecto.Multi.run(:post, fn repo, _changes ->
     case repo.get(Post, 1) do
       nil -> {:error, :not_found}
       post -> {:ok, post}
     end
   end)
|> Ecto.Multi.delete(:delete, fn %{post: post} ->
     # Others validations
     post
   end)
|> MyApp.Repo.transaction()

delete_all(multi, name, queryable, opts \\ [])

delete_all(t(), name(), Ecto.Queryable.t(), Keyword.t()) :: t()

Adds a delete_all operation to the multi.

Accepts the same arguments and options as Ecto.Repo.delete_all/2 does.

Example

queryable = from(p in Post, where: p.id < 5)
Ecto.Multi.new()
|> Ecto.Multi.delete_all(:delete_all, queryable)
|> MyApp.Repo.transaction()

error(multi, name, value)

error(t(), name(), error :: term()) :: t()

Causes the multi to fail with the given value.

Running the multi in a transaction will execute no previous steps and returns the value of the first error added.

insert(multi, name, changeset_or_struct_or_fun, opts \\ [])

insert(
  t(),
  name(),
  Ecto.Changeset.t()
  | Ecto.Schema.t()
  | fun(Ecto.Changeset.t() | Ecto.Schema.t()),
  Keyword.t()
) :: t()

Adds an insert operation to the multi.

Accepts the same arguments and options as Ecto.Repo.insert/2 does.

Example

Ecto.Multi.new()
|> Ecto.Multi.insert(:insert, %Post{title: "first"})
|> MyApp.Repo.transaction()

Ecto.Multi.new()
|> Ecto.Multi.insert(:post, %Post{title: "first"})
|> Ecto.Multi.insert(:comment, fn %{post: post} ->
     Ecto.build_assoc(post, :comments)
   end)
|> MyApp.Repo.transaction()

insert_all(multi, name, schema_or_source, entries, opts \\ [])

insert_all(
  t(),
  name(),
  schema_or_source(),
  [map() | Keyword.t()],
  Keyword.t()
) :: t()

Adds an insert_all operation to the multi.

Accepts the same arguments and options as Ecto.Repo.insert_all/3 does.

Example

posts = [%{title: "My first post"}, %{title: "My second post"}]
Ecto.Multi.new()
|> Ecto.Multi.insert_all(:insert_all, Post, posts)
|> MyApp.Repo.transaction()

insert_or_update(multi, name, changeset, opts \\ [])

insert_or_update(
  t(),
  name(),
  Ecto.Changeset.t() | fun(Ecto.Changeset.t()),
  Keyword.t()
) :: t()

Inserts or updates a changeset depending on whether the changeset was persisted or not.

Accepts the same arguments and options as Ecto.Repo.insert_or_update/2 does.

Example

changeset = Post.changeset(%Post{}, %{title: "New title"})
Ecto.Multi.new()
|> Ecto.Multi.insert_or_update(:insert_or_update, changeset)
|> MyApp.Repo.transaction()

Ecto.Multi.new()
|> Ecto.Multi.run(:post, fn repo, _changes ->
     {:ok, repo.get(Post, 1) || %Post{}}
   end)
|> Ecto.Multi.insert_or_update(:update, fn %{post: post} ->
     Ecto.Changeset.change(post, title: "New title")
   end)
|> MyApp.Repo.transaction()

merge(multi, merge)

merge(t(), (changes() -> t())) :: t()

Merges a multi returned dynamically by an anonymous function.

This function is useful when the multi to be merged requires information from the original multi. Hence the second argument is an anonymous function that receives the multi changes so far. The anonymous function must return another multi.

If you would prefer to simply merge two multis together, see append/2 or prepend/2.

Duplicated operations are not allowed.

Example

multi =
  Ecto.Multi.new()
  |> Ecto.Multi.insert(:post, %Post{title: "first"})

multi
|> Ecto.Multi.merge(fn %{post: post} ->
  Ecto.Multi.new()
  |> Ecto.Multi.insert(:comment, Ecto.build_assoc(post, :comments))
end)
|> MyApp.Repo.transaction()

merge(multi, mod, fun, args)

merge(t(), module(), function, args) :: t()
when function: atom(), args: [any()]

Merges a multi returned dynamically by calling module and function with args.

Similar to merge/2, but allows to pass module name, function and arguments. The function should return an Ecto.Multi, and receives changes so far as the first argument (prepended to those passed in the call to the function).

Duplicated operations are not allowed.

new()

new() :: t()

Returns an empty Ecto.Multi struct.

Example

iex> Ecto.Multi.new() |> Ecto.Multi.to_list()
[]

prepend(lhs, rhs)

prepend(t(), t()) :: t()

Prepends the second multi to the first one.

All names must be unique between both structures.

Example

iex> lhs = Ecto.Multi.new() |> Ecto.Multi.run(:left, fn _, changes -> {:ok, changes} end)
iex> rhs = Ecto.Multi.new() |> Ecto.Multi.run(:right, fn _, changes -> {:error, changes} end)
iex> Ecto.Multi.prepend(lhs, rhs) |> Ecto.Multi.to_list |> Keyword.keys
[:right, :left]

run(multi, name, run)

run(t(), name(), run()) :: t()

Adds a function to run as part of the multi.

The function should return either {:ok, value} or {:error, value}, and receives the repo as the first argument, and the changes so far as the second argument.

Example

Ecto.Multi.run(multi, :write, fn _repo, %{image: image} ->
  with :ok <- File.write(image.name, image.contents) do
    {:ok, nil}
  end
end)

run(multi, name, mod, fun, args)

run(t(), name(), module(), function, args) :: t()
when function: atom(), args: [any()]

Adds a function to run as part of the multi.

Similar to run/3, but allows to pass module name, function and arguments. The function should return either {:ok, value} or {:error, value}, and receives the repo as the first argument, and the changes so far as the second argument (prepended to those passed in the call to the function).

to_list(multi)

to_list(t()) :: [{name(), term()}]

Returns the list of operations stored in multi.

Always use this function when you need to access the operations you have defined in Ecto.Multi. Inspecting the Ecto.Multi struct internals directly is discouraged.

update(multi, name, changeset_or_fun, opts \\ [])

update(
  t(),
  name(),
  Ecto.Changeset.t() | fun(Ecto.Changeset.t()),
  Keyword.t()
) :: t()

Adds an update operation to the multi.

Accepts the same arguments and options as Ecto.Repo.update/2 does.

Example

post = MyApp.Repo.get!(Post, 1)
changeset = Ecto.Changeset.change(post, title: "New title")
Ecto.Multi.new()
|> Ecto.Multi.update(:update, changeset)
|> MyApp.Repo.transaction()

Ecto.Multi.new()
|> Ecto.Multi.insert(:post, %Post{title: "first"})
|> Ecto.Multi.update(:fun, fn %{post: post} ->
     Ecto.Changeset.change(post, title: "New title")
   end)
|> MyApp.Repo.transaction()

update_all(multi, name, queryable, updates, opts \\ [])

update_all(t(), name(), Ecto.Queryable.t(), Keyword.t(), Keyword.t()) ::
  t()

Adds an update_all operation to the multi.

Accepts the same arguments and options as Ecto.Repo.update_all/3 does.

Example

Ecto.Multi.new()
|> Ecto.Multi.update_all(:update_all, Post, set: [title: "New title"])
|> MyApp.Repo.transaction()