Ecto v3.0.1 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
Functions
Appends the second multi to the first one
Adds a delete operation to the multi
Adds a delete_all operation to the multi
Causes the multi to fail with the given value
Adds an insert operation to the multi
Adds an insert_all operation to the multi
Inserts or updates a changeset depending on whether the changeset was persisted or not
Merges a multi returned dynamically by an anonymous function
Merges a multi returned dynamically by calling module
and function
with args
Returns an empty Ecto.Multi
struct
Prepends the second multi to the first one
Adds a function to run as part of the multi
Adds a function to run as part of the multi
Returns the list of operations stored in multi
Adds an update operation to the multi
Adds an update_all operation to the multi
Link to this section Types
Link to this section Functions
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( 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 ->
MyApp.Repo.get!(Post, 1)
end)
|> Ecto.Multi.delete(:delete, fn %{post: post} ->
# Others validations
post
end)
|> MyApp.Repo.transaction()
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()
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( 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()
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( 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 ->
MyApp.Repo.get!(Post, 1)
end)
|> Ecto.Multi.insert_or_update(:update, fn %{post: post} ->
Ecto.Changeset.change(post, title: "New title")
end)
|> MyApp.Repo.transaction()
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
Ecto.Multi.merge(multi, fn %{post: post} ->
Ecto.Multi.new()
|> Ecto.Multi.insert(:comment, Ecto.build_assoc(post, :comments))
end)
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.
Returns an empty Ecto.Multi
struct.
Example
iex> Ecto.Multi.new |> Ecto.Multi.to_list
[]
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]
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, fn _repo, %{image: image} ->
File.write!(image.name, image.contents)
end)
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).
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( 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()
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()