Ecto.Migrator (Ecto SQL v3.7.1) View Source

Lower level API for managing migrations.

EctoSQL provides three mix tasks for running and managing migrations:

mix ecto.migrate - migrates a repository
mix ecto.rollback - rolls back a particular migration
mix ecto.migrations - shows all migrations and their status

Those tasks are built on top of the functions in this module. While the tasks above cover most use cases, it may be necessary from time to time to jump into the lower level API. For example, if you are assembling an Elixir release, Mix is not available, so this module provides a nice complement to still migrate your system.

To learn more about migrations in general, see Ecto.Migration.

Example: Running an individual migration

Imagine you have this migration:

defmodule MyApp.MigrationExample do
  use Ecto.Migration

  def up do
    execute "CREATE TABLE users(id serial PRIMARY_KEY, username text)"
  end

  def down do
    execute "DROP TABLE users"
  end
end

You can execute it manually with:

Ecto.Migrator.up(Repo, 20080906120000, MyApp.MigrationExample)

Example: Running migrations in a release

Elixir v1.9 introduces mix release, which generates a self-contained directory that consists of your application code, all of its dependencies, plus the whole Erlang Virtual Machine (VM) and runtime.

When a release is assembled, Mix is no longer available inside a release and therefore none of the Mix tasks. Users may still need a mechanism to migrate their databases. This can be achieved with using the Ecto.Migrator module:

defmodule MyApp.Release do
  @app :my_app

  def migrate do
    for repo <- repos() do
      {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :up, all: true))
    end
  end

  def rollback(repo, version) do
    {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :down, to: version))
  end

  defp repos do
    Application.load(@app)
    Application.fetch_env!(@app, :ecto_repos)
  end
end

The example above uses with_repo/3 to make sure the repository is started and then runs all migrations up or a given migration down. Note you will have to replace MyApp and :my_app on the first two lines by your actual application name. Once the file above is added to your application, you can assemble a new release and invoke the commands above in the release root like this:

$ bin/my_app eval "MyApp.Release.migrate"
$ bin/my_app eval "MyApp.Release.rollback(MyApp.Repo, 20190417140000)"

Link to this section Summary

Functions

down(repo, version, module, opts \\ [])

Runs a down migration on the given repository.

migrated_versions(repo, opts \\ [])

Gets all migrated versions.

migrations(repo)

Returns an array of tuples as the migration status of the given repo, without actually running any migrations.

migrations(repo, directories, opts \\ [])

Returns an array of tuples as the migration status of the given repo, without actually running any migrations.

migrations_path(repo, directory \\ "migrations")

Gets the migrations path from a repository.

run(repo, direction, opts)

Runs migrations for the given repository.

run(repo, migration_source, direction, opts)

Apply migrations to a repository with a given strategy.

up(repo, version, module, opts \\ [])

Runs an up migration on the given repository.

with_repo(repo, fun, opts \\ [])

Ensures the repo is started to perform migration operations.

Link to this section Functions

down(repo, version, module, opts \\ [])

Runs a down migration on the given repository.

Options

:log - the level to use for logging of migration commands. Defaults to :info. Can be any of Logger.level/0 values or a boolean.
:log_migrations_sql - the level to use for logging of SQL commands generated by migrations. Defaults to false. Can be any of Logger.level/0 values or a boolean.
:log_migrator_sql - the level to use for logging of SQL commands emitted by the migrator, such as transactions, locks, etc. Defaults to false. Can be any of Logger.level/0 values or a boolean.
:prefix - the prefix to run the migrations on
:dynamic_repo - the name of the Repo supervisor process. See Ecto.Repo.put_dynamic_repo/1.

migrated_versions(repo, opts \\ [])

Specs

migrated_versions(Ecto.Repo.t(), Keyword.t()) :: [integer()]

Gets all migrated versions.

This function ensures the migration table exists if no table has been defined yet.

Options

:prefix - the prefix to run the migrations on
:dynamic_repo - the name of the Repo supervisor process. See Ecto.Repo.put_dynamic_repo/1.
:skip_table_creation - skips any attempt to create the migration table Useful for situations where user needs to check migrations but has insufficient permissions to create the table. Note that migrations commands may fail if this is set to true. Defaults to false. Accepts a boolean.

migrations(repo)

Specs

migrations(Ecto.Repo.t()) :: [
  {:up | :down, id :: integer(), name :: String.t()}
]

Returns an array of tuples as the migration status of the given repo, without actually running any migrations.

Equivalent to:

Ecto.Migrator.migrations(repo, [Ecto.Migrator.migrations_path(repo)])

migrations(repo, directories, opts \\ [])

Specs

migrations(Ecto.Repo.t(), [String.t()], Keyword.t()) :: [
  {:up | :down, id :: integer(), name :: String.t()}
]

Returns an array of tuples as the migration status of the given repo, without actually running any migrations.

migrations_path(repo, directory \\ "migrations")

Specs

migrations_path(Ecto.Repo.t(), String.t()) :: String.t()

Gets the migrations path from a repository.

This function accepts an optional second parameter to customize the migrations directory. This can be used to specify a custom migrations path.

run(repo, direction, opts)

Specs

run(Ecto.Repo.t(), atom(), Keyword.t()) :: [integer()]

Runs migrations for the given repository.

Equivalent to:

Ecto.Migrator.run(repo, [Ecto.Migrator.migrations_path(repo)], direction, opts)

See run/4 for more information.

run(repo, migration_source, direction, opts)

Specs

run(
  Ecto.Repo.t(),
  String.t() | [String.t()] | [{integer(), module()}],
  atom(),
  Keyword.t()
) :: [integer()]

Apply migrations to a repository with a given strategy.

The second argument identifies where the migrations are sourced from. A binary representing directory (or a list of binaries representing directories) may be passed, in which case we will load all files following the "#{VERSION}_#{NAME}.exs" schema. The migration_source may also be a list of tuples that identify the version number and migration modules to be run, for example:

Ecto.Migrator.run(Repo, [{0, MyApp.Migration1}, {1, MyApp.Migration2}, ...], :up, opts)

A strategy (which is one of :all, :step or :to) must be given as an option.

Execution model

In order to run migrations, at least two database connections are necessary. One is used to lock the "schema_migrations" table and the other one to effectively run the migrations. This allows multiple nodes to run migrations at the same time, but guarantee that only one of them will effectively migrate the database.

A downside of this approach is that migrations cannot run dynamically during test under the Ecto.Adapters.SQL.Sandbox, as the sandbox has to share a single connection across processes to guarantee the changes can be reverted.

Options

:all - runs all available if true
:step - runs the specific number of migrations
:to - runs all until the supplied version is reached (including the version given in :to)

Plus all other options described in up/4.

up(repo, version, module, opts \\ [])

Specs

up(Ecto.Repo.t(), integer(), module(), Keyword.t()) :: :ok | :already_up

Runs an up migration on the given repository.

Options

:log - the level to use for logging of migration instructions. Defaults to :info. Can be any of Logger.level/0 values or a boolean.
:log_migrations_sql - the level to use for logging of SQL commands generated by migrations. Defaults to false. Can be any of Logger.level/0 values or a boolean.
:log_migrator_sql - the level to use for logging of SQL commands emitted by the migrator, such as transactions, locks, etc. Defaults to false.
:prefix - the prefix to run the migrations on
:dynamic_repo - the name of the Repo supervisor process. See Ecto.Repo.put_dynamic_repo/1.
:strict_version_order - abort when applying a migration with old timestamp (otherwise it emits a warning)

with_repo(repo, fun, opts \\ [])

Ensures the repo is started to perform migration operations.

All of the application required to run the repo will be started before hand with chosen mode. If the repo has not yet been started, it is manually started, with a :pool_size of 2, before the given function is executed, and the repo is then terminated. If the repo was already started, then the function is directly executed, without terminating the repo afterwards.

Although this function was designed to start repositories for running migrations, it can be used by any code, Mix task, or release tooling that needs to briefly start a repository to perform a certain operation and then terminate.

The repo may also configure a :start_apps_before_migration option which is a list of applications to be started before the migration runs.

It returns {:ok, fun_return, apps}, with all apps that have been started, or {:error, term}.

Options

:pool_size - The pool size to start the repo for migrations. Defaults to 2.
:mode - The mode to start all applications. Defaults to :permanent.

Examples

{:ok, _, _} =
  Ecto.Migrator.with_repo(repo, fn repo ->
    Ecto.Migrator.run(repo, :up, all: true)
  end)