Ecto.Multi
Ecto.Multi
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.
Run
Multi allows you to run arbitrary functions as part of your transaction via the run/3
and run/5
. This is very useful when an operation depends on the value of a previous operation. For this reason, the function given as callback to run/3
and run/5
will receive all changes performed by the multi so far as a map in the first 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
Summary
Types
Functions
- append(lhs, rhs)
-
Appends the second multi to the first one
- delete(multi, name, changeset_or_struct, 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, 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
- 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
andfunction
withargs
- 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, opts \\ [])
-
Adds an update operation to the multi
- update_all(multi, name, queryable, updates, opts \\ [])
-
Adds an update_all operation to the multi
Types
merge()
merge() :: (map -> t) | {module, atom, [any]}
name()
name() :: any
run()
run() :: (t -> {:ok | :error, any}) | {module, atom, [any]}
t()
t
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, &{:ok, &1})
iex> rhs = Ecto.Multi.new |> Ecto.Multi.run(:right, &{:error, &1})
iex> Ecto.Multi.append(lhs, rhs) |> Ecto.Multi.to_list |> Keyword.keys
[:left, :right]
delete(multi, name, changeset_or_struct, opts \\ [])
delete(t, name, 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/3
does.
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.
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 all previous steps until this operation which halt with the given value
.
insert(multi, name, changeset_or_struct, opts \\ [])
insert(t, name, 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.
insert_all(multi, name, schema_or_source, entries, opts \\ [])
insert_all(t, name, schema_or_source, [entry], Keyword.t) :: t when schema_or_source: binary | {binary | nil, binary} | Ecto.Schema.t, entry: map | Keyword.t
Adds an insert_all operation to the multi.
Accepts the same arguments and options as Ecto.Repo.insert_all/3
does.
merge(multi, merge)
merge(t, (t -> {:ok | :error, any})) :: 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.
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, &{:ok, &1})
iex> rhs = Ecto.Multi.new |> Ecto.Multi.run(:right, &{:error, &1})
iex> Ecto.Multi.prepend(lhs, rhs) |> Ecto.Multi.to_list |> Keyword.keys
[:right, :left]
run(multi, name, run)
run(t, name, (t -> {:ok | :error, any})) :: t
Adds a function to run as part of the multi.
The function should return either {:ok, value}
or {:error, value}
, and receives changes so far as an argument.
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 will receive changes so far as the first argument (prepended to those passed in the call to the function).
to_list(multi)
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, opts \\ [])
update(t, name, 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.
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.
© 2012 Plataformatec
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/ecto/Ecto.Multi.html