Welcome to Flask-Migrate's documentation!
*****************************************

**Flask-Migrate** is an extension that handles SQLAlchemy database
migrations for Flask applications using Alembic. The database
operations are made available through the Flask command-line interface
or through the Flask-Script extension.


Installation
============

Install Flask-Migrate with *pip*:

   pip install Flask-Migrate


Example
=======

This is an example application that handles database migrations
through Flask-Migrate:

   from flask import Flask
   from flask_sqlalchemy import SQLAlchemy
   from flask_migrate import Migrate

   app = Flask(__name__)
   app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///app.db'

   db = SQLAlchemy(app)
   migrate = Migrate(app, db)

   class User(db.Model):
       id = db.Column(db.Integer, primary_key=True)
       name = db.Column(db.String(128))

With the above application you can create a migration repository with
the following command:

   $ flask db init

This will add a *migrations* folder to your application. The contents
of this folder need to be added to version control along with your
other source files.

You can then generate an initial migration:

   $ flask db migrate

The migration script needs to be reviewed and edited, as Alembic
currently does not detect every change you make to your models. In
particular, Alembic is currently unable to detect table name changes,
column name changes, or anonymously named constraints. A detailed
summary of limitations can be found in the Alembic autogenerate
documentation. Once finalized, the migration script also needs to be
added to version control.

Then you can apply the migration to the database:

   $ flask db upgrade

Then each time the database models change repeat the "migrate" and
"upgrade" commands.

To sync the database in another system just refresh the *migrations*
folder from source control and run the "upgrade" command.

To see all the commands that are available run this command:

   $ flask db --help

Note that the application script must be set in the "FLASK_APP"
environment variable for all the above commands to work, as required
by the "flask" command line script.


Using Flask-Script
==================

Flask-Migrate also supports the Flask-Script command-line interface.
This is an example application that exposes all the database migration
commands through Flask-Script:

   from flask import Flask
   from flask_sqlalchemy import SQLAlchemy
   from flask_script import Manager
   from flask_migrate import Migrate, MigrateCommand

   app = Flask(__name__)
   app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///app.db'

   db = SQLAlchemy(app)
   migrate = Migrate(app, db)

   manager = Manager(app)
   manager.add_command('db', MigrateCommand)

   class User(db.Model):
       id = db.Column(db.Integer, primary_key=True)
       name = db.Column(db.String(128))

   if __name__ == '__main__':
       manager.run()

Assuming the above script is stored in a file named "manage.py", all
the database migration commands can be accessed by running the script:

   $ python manage.py db init
   $ python manage.py db migrate
   $ python manage.py db upgrade
   $ python manage.py db --help


Configuration Callbacks
=======================

Sometimes applications need to dynamically insert their own settings
into the Alembic configuration. A function decorated with the
"configure" callback will be invoked after the configuration is read,
and before it is used. The function can modify the configuration
object, or replace it with a different one.

   @migrate.configure
   def configure_alembic(config):
       # modify config object
       return config

Multiple configuration callbacks can be defined simply by decorating
multiple functions. The order in which multiple callbacks are invoked
is undetermined.


Multiple Database Support
=========================

Flask-Migrate can integrate with the  binds feature of Flask-
SQLAlchemy, making it possible to track migrations to multiple
databases associated with an application.

To create a multiple database migration repository, add the "--
multidb" argument to the "init" command:

   $ flask db init --multidb

With this command, the migration repository will be set up to track
migrations on your main database, and on any additional databases
defined in the "SQLALCHEMY_BINDS" configuration option.


Command Reference
=================

Flask-Migrate exposes two classes, "Migrate" and "MigrateCommand". The
"Migrate" class contains all the functionality of the extension. The
"MigrateCommand" class is only used when it is desired to expose
database migration commands through the Flask-Script extension.

The following example initializes the extension with the standard
Flask command-line interface:

   from flask_migrate import Migrate
   migrate = Migrate(app, db)

The two arguments to "Migrate" are the application instance and the
Flask-SQLAlchemy database instance. The "Migrate" constructor also
takes additional keyword arguments, which are passed to Alembic's
"EnvironmentContext.configure()" method. As is standard for all Flask
extensions, Flask-Migrate can be initialized using the "init_app"
method as well.

When using Flask-Script's command-line interface, the extension is
initialized as follows:

   from flask_migrate import Migrate, MigrateCommand
   migrate = Migrate(app, db)
   manager.add_command('db', MigrateCommand)

After the extension is initialized, a "db" group will be added to the
command-line options with several sub-commands, both in the "flask"
command or with a "manage.py" type script created with Flask-Script.
Below is a list of the available sub-commands:

* "flask db --help"

     Shows a list of available commands.

* "flask db init [--multidb]"

     Initializes migration support for the application. The optional "
     --multidb" enables migrations for multiple databases configured
     as Flask-SQLAlchemy binds.

* "flask db revision [--message MESSAGE] [--autogenerate] [--sql]
  [--head HEAD] [--splice] [--branch-label BRANCH_LABEL] [--version-
  path VERSION_PATH] [--rev-id REV_ID]"

     Creates an empty revision script. The script needs to be edited
     manually with the upgrade and downgrade changes. See Alembic's
     documentation for instructions on how to write migration scripts.
     An optional migration message can be included.

* "flask db migrate [--message MESSAGE] [--sql] [--head HEAD]
  [--splice] [--branch-label BRANCH_LABEL] [--version-path
  VERSION_PATH] [--rev-id REV_ID]"

     Equivalent to "revision --autogenerate". The migration script is
     populated with changes detected automatically. The generated
     script should to be reviewed and edited as not all types of
     changes can be detected automatically. This command does not make
     any changes to the database, just creates the revision script.

* "flask db edit <revision>"

     Edit a revision script using $EDITOR.

* "flask db upgrade [--sql] [--tag TAG] [--x-arg ARG] <revision>"

     Upgrades the database. If "revision" isn't given then ""head"" is
     assumed.

* "flask db downgrade [--sql] [--tag TAG] [--x-arg ARG] <revision>"

     Downgrades the database. If "revision" isn't given then "-1" is
     assumed.

* "flask db stamp [--sql] [--tag TAG] <revision>"

     Sets the revision in the database to the one given as an
     argument, without performing any migrations.

* "flask db current [--verbose]"

     Shows the current revision of the database.

* "flask db history [--rev-range REV_RANGE] [--verbose]"

     Shows the list of migrations. If a range isn't given then the
     entire history is shown.

* "flask db show <revision>"

     Show the revision denoted by the given symbol.

* "flask db merge [--message MESSAGE] [--branch-label BRANCH_LABEL]
  [--rev-id REV_ID] <revisions>"

     Merge two revisions together. Creates a new revision file.

* "flask db heads [--verbose] [--resolve-dependencies]"

     Show current available heads in the revision script directory.

* "flask db branches [--verbose]"

     Show current branch points.

Notes:

* All commands also take a "--directory DIRECTORY" option that
  points to the directory containing the migration scripts. If this
  argument is omitted the directory used is "migrations".

* The default directory can also be specified as a "directory"
  argument to the "Migrate" constructor.

* The "--sql" option present in several commands performs an
  'offline' mode migration. Instead of executing the database commands
  the SQL statements that need to be executed are printed to the
  console.

* Detailed documentation on these commands can be found in the
  Alembic's command reference page.


API Reference
=============

The commands exposed by Flask-Migrate's command-line interface can
also be accessed programmatically by importing the functions from
module "flask_migrate". The available functions are:

* "init(directory='migrations', multidb=False)"

     Initializes migration support for the application.

* "revision(directory='migrations', message=None,
  autogenerate=False, sql=False, head='head', splice=False,
  branch_label=None, version_path=None, rev_id=None)"

     Creates an empty revision script.

* "migrate(directory='migrations', message=None, sql=False,
  head='head', splice=False, branch_label=None, version_path=None,
  rev_id=None)"

     Creates an automatic revision script.

* "edit(directory='migrations', revision='head')"

     Edit revision script(s) using $EDITOR.

* "merge(directory='migrations', revisions='', message=None,
  branch_label=None, rev_id=None)"

     Merge two revisions together.  Creates a new migration file.

* "upgrade(directory='migrations', revision='head', sql=False,
  tag=None)"

     Upgrades the database.

* "downgrade(directory='migrations', revision='-1', sql=False,
  tag=None)"

     Downgrades the database.

* "show(directory='migrations', revision='head')"

     Show the revision denoted by the given symbol.

* "history(directory='migrations', rev_range=None, verbose=False)"

     Shows the list of migrations. If a range isn't given then the
     entire history is shown.

* "heads(directory='migrations', verbose=False,
  resolve_dependencies=False)"

     Show current available heads in the script directory.

* "branches(directory='migrations', verbose=False)"

     Show current branch points

* "current(directory='migrations', verbose=False, head_only=False)"

     Shows the current revision of the database.

* "stamp(directory='migrations', revision='head', sql=False,
  tag=None)"

     Sets the revision in the database to the one given as an
     argument, without performing any migrations.

Note: For greater scripting flexibility you can also use the API
exposed by Alembic directly.
