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Code Issues 32 Releases Wiki Activity

Improved formatting and links of migration docs.

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Tim Graham
2014-04-27 15:05:25 -04:00
parent 8905fcbda6
commit ab8d8e00c9
4 changed files with 128 additions and 166 deletions
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111
docs/ref/migration-operations.txt
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@@ -2,39 +2,39 @@
Migration Operations
====================
Migration files are composed of one or more Operations, objects that
.. module:: django.db.migrations.operations
Migration files are composed of one or more ``Operation``\s, objects that
declaratively record what the migration should do to your database.
Django also uses these Operation objects to work out what your models
Django also uses these ``Operation`` objects to work out what your models
looked like historically, and to calculate what changes you've made to
your models since the last migration so it can automatically write
your migrations; that's why they're declarative, as it means Django can
easily load them all into memory and run through them without touching
the database to work out what your project should look like.
There are also more specialized Operation objects which are for things like
There are also more specialized ``Operation`` objects which are for things like
:ref:`data migrations <data-migrations>` and for advanced manual database
manipulation. You can also write your own Operation classes if you want
manipulation. You can also write your own ``Operation`` classes if you want
to encapsulate a custom change you commonly make.
If you need an empty migration file to write your own Operation objects
If you need an empty migration file to write your own ``Operation`` objects
into, just use ``python manage.py makemigrations --empty yourappname``,
but be aware that manually adding schema-altering operations can confuse the
migration autodetector and make resulting runs of ``makemigrations`` output
incorrect code.
migration autodetector and make resulting runs of :djadmin:`makemigrations`
output incorrect code.
All of the core Django operations are available from the
``django.db.migrations.operations`` module.
Schema Operations
=================
CreateModel
-----------
::
CreateModel(name, fields, options=None, bases=None)
.. class:: CreateModel(name, fields, options=None, bases=None)
Creates a new model in the project history and a corresponding table in the
database to match it.
@@ -53,21 +53,17 @@ it can contain both class objects as well as strings in the format
from the historical version). If it's not supplied, it defaults to just
inheriting from the standard ``models.Model``.
DeleteModel
-----------
::
DeleteModel(name)
.. class:: DeleteModel(name)
Deletes the model from the project history and its table from the database.
RenameModel
-----------
::
RenameModel(old_name, new_name)
.. class:: RenameModel(old_name, new_name)
Renames the model from an old name to a new one.
@@ -77,41 +73,36 @@ the autodetector, this will look like you deleted a model with the old name
and added a new one with a different name, and the migration it creates will
lose any data in the old table.
AlterModelTable
---------------
::
AlterModelTable(name, table)
Changes the model's table name (the ``db_table`` option on the ``Meta`` subclass)
.. class:: AlterModelTable(name, table)
Changes the model's table name (the :attr:`~django.db.models.Options.db_table`
option on the ``Meta`` subclass).
AlterUniqueTogether
-------------------
::
AlterUniqueTogether(name, unique_together)
Changes the model's set of unique constraints
(the ``unique_together`` option on the ``Meta`` subclass)
.. class:: AlterUniqueTogether(name, unique_together)
Changes the model's set of unique constraints (the
:attr:`~django.db.models.Options.unique_together` option on the ``Meta``
subclass).
AlterIndexTogether
------------------
::
AlterIndexTogether(name, index_together)
Changes the model's set of custom indexes
(the ``index_together`` option on the ``Meta`` subclass)
.. class:: AlterIndexTogether(name, index_together)
Changes the model's set of custom indexes (the
:attr:`~django.db.models.Options.index_together` option on the ``Meta``
subclass).
AddField
--------
::
AddField(model_name, name, field, preserve_default=True)
.. class:: AddField(model_name, name, field, preserve_default=True)
Adds a field to a model. ``model_name`` is the model's name, ``name`` is
the field's name, and ``field`` is an unbound Field instance (the thing
@@ -126,12 +117,10 @@ a default value to put into existing rows. It does not effect the behavior
of setting defaults in the database directly - Django never sets database
defaults, and always applies them in the Django ORM code.
RemoveField
-----------
::
RemoveField(model_name, name)
.. class:: RemoveField(model_name, name)
Removes a field from a model.
@@ -139,42 +128,34 @@ Bear in mind that when reversed this is actually adding a field to a model;
if the field is not nullable this may make this operation irreversible (apart
from any data loss, which of course is irreversible).
AlterField
----------
::
AlterField(model_name, name, field)
.. class:: AlterField(model_name, name, field)
Alters a field's definition, including changes to its type, ``null``, ``unique``,
``db_column`` and other field attributes.
Alters a field's definition, including changes to its type,
:attr:`~django.db.models.Field.null`, :attr:`~django.db.models.Field.unique`,
:attr:`~django.db.models.Field.db_column` and other field attributes.
Note that not all changes are possible on all databases - for example, you
cannot change a text-type field like ``models.TextField()`` into a number-type
field like ``models.IntegerField()`` on most databases.
RenameField
-----------
::
RenameField(model_name, old_name, new_name)
Changes a field's name (and, unless ``db_column`` is set, its column name).
.. class:: RenameField(model_name, old_name, new_name)
Changes a field's name (and, unless :attr:`~django.db.models.Field.db_column`
is set, its column name).
Special Operations
==================
.. _operation-run-sql:
RunSQL
------
::
RunSQL(sql, reverse_sql=None, state_operations=None)
.. class:: RunSQL(sql, reverse_sql=None, state_operations=None)
Allows running of arbitrary SQL on the database - useful for more advanced
features of database backends that Django doesn't support directly, like
@@ -194,24 +175,22 @@ operation that adds that field and so will try to run it again).
.. _sqlparse: https://pypi.python.org/pypi/sqlparse
.. _operation-run-python:
RunPython
---------
::
RunPython(code, reverse_code=None)
.. class:: RunPython(code, reverse_code=None)
Runs custom Python code in a historical context. ``code`` (and ``reverse_code``
if supplied) should be callable objects that accept two arguments; the first is
an instance of ``django.apps.registry.Apps`` containing historical models that
match the operation's place in the project history, and the second is an
instance of SchemaEditor.
instance of :class:`SchemaEditor
<django.db.backends.schema.BaseDatabaseSchemaEditor>`.
You are advised to write the code as a separate function above the ``Migration``
class in the migration file, and just pass it to ``RunPython``. Here's an
example of using RunPython to create some initial objects on a Country model::
example of using ``RunPython`` to create some initial objects on a ``Country``
model::
# encoding: utf8
from django.db import models, migrations
@@ -245,19 +224,16 @@ or ``orm["appname", "Model"]`` references from South directly into
``apps.get_model("appname", "Model")`` references here and leave most of the
rest of the code unchanged for data migrations.
Much like ``RunSQL``, ensure that if you change schema inside here you're
Much like :class:`RunSQL`, ensure that if you change schema inside here you're
either doing it outside the scope of the Django model system (e.g. triggers)
or that you use ``SeparateDatabaseAndState`` to add in operations that will
or that you use :class:`SeparateDatabaseAndState` to add in operations that will
reflect your changes to the model state - otherwise, the versioned ORM and
the autodetector will stop working correctly.
SeparateDatabaseAndState
------------------------
::
SeparateDatabaseAndState(database_operations=None, state_operations=None)
.. class:: SeparateDatabaseAndState(database_operations=None, state_operations=None)
A highly specialized operation that let you mix and match the database
(schema-changing) and state (autodetector-powering) aspects of operations.
@@ -266,13 +242,12 @@ It accepts two list of operations, and when asked to apply state will use the
state list, and when asked to apply changes to the database will use the database
list. Do not use this operation unless you're very sure you know what you're doing.
Writing your own
================
Operations have a relatively simple API, and they're designed so that you can
easily write your own to supplement the built-in Django ones. The basic structure
of an Operation looks like this::
of an ``Operation`` looks like this::
from django.db.migrations.operations.base import Operation
@@ -317,7 +292,7 @@ historical models.
Some things to note:
* You don't need to learn too much about ProjectState to just write simple
* You don't need to learn too much about ``ProjectState`` to just write simple
migrations; just know that it has a ``.render()`` method that turns it into
an app registry (which you can then call ``get_model`` on).

92
docs/ref/schema-editor.txt
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@@ -1,6 +1,10 @@
============
SchemaEditor
============
================
``SchemaEditor``
================
.. module:: django.db.backends.schema
.. class:: BaseDatabaseSchemaEditor
Django's migration system is split into two parts; the logic for calculating
and storing what operations should be run (``django.db.migrations``), and the
@@ -27,10 +31,10 @@ of change are not possible on all databases - for example, MyISAM does not
support foreign key constraints.
If you are writing or maintaining a third-party database backend for Django,
you will need to provide a SchemaEditor implementation in order to work with
you will need to provide a ``SchemaEditor`` implementation in order to work with
1.7's migration functionality - however, as long as your database is relatively
standard in its use of SQL and relational design, you should be able to
subclass one of the built-in Django SchemaEditor classes and just tweak the
subclass one of the built-in Django ``SchemaEditor`` classes and just tweak the
syntax a little. Also note that there are a few new database features that
migrations will look for: ``can_rollback_ddl`` and
``supports_combined_alters`` are the most important.
@@ -41,9 +45,7 @@ Methods
execute
-------
::
execute(sql, params=[])
.. method:: BaseDatabaseSchemaEditor.execute(sql, params=[])
Executes the SQL statement passed in, with parameters if supplied. This
is a simple wrapper around the normal database cursors that allows
@@ -52,92 +54,71 @@ capture of the SQL to a ``.sql`` file if the user wishes.
create_model
------------
::
create_model(model)
.. method:: BaseDatabaseSchemaEditor.create_model(model)
Creates a new table in the database for the provided model, along with any
unique constraints or indexes it requires.
delete_model
------------
::
delete_model(model)
.. method:: BaseDatabaseSchemaEditor.delete_model(model)
Drops the model's table in the database along with any unique constraints
or indexes it has.
alter_unique_together
---------------------
::
alter_unique_together(model, old_unique_together, new_unique_together)
Changes a model's unique_together value; this will add or remove unique
constraints from the model's table until they match the new value.
.. method:: BaseDatabaseSchemaEditor.alter_unique_together(model, old_unique_together, new_unique_together)
Changes a model's :attr:`~django.db.models.Options.unique_together` value; this
will add or remove unique constraints from the model's table until they match
the new value.
alter_index_together
--------------------
::
alter_index_together(model, old_index_together, new_index_together)
Changes a model's index_together value; this will add or remove indexes
from the model's table until they match the new value.
.. method:: BaseDatabaseSchemaEditor.alter_index_together(model, old_index_together, new_index_together)
Changes a model's :attr:`~django.db.models.Options.index_together` value; this
will add or remove indexes from the model's table until they match the new
value.
alter_db_table
--------------
::
alter_db_table(model, old_db_table, new_db_table)
.. method:: BaseDatabaseSchemaEditor.alter_db_table(model, old_db_table, new_db_table)
Renames the model's table from ``old_db_table`` to ``new_db_table``.
alter_db_tablespace
-------------------
::
alter_db_tablespace(model, old_db_tablespace, new_db_tablespace)
.. method:: BaseDatabaseSchemaEditor.alter_db_tablespace(model, old_db_tablespace, new_db_tablespace)
Moves the model's table from one tablespace to another.
add_field
---------
::
add_field(model, field)
.. method:: BaseDatabaseSchemaEditor.add_field(model, field)
Adds a column (or sometimes multiple) to the model's table to represent the
field. This will also add indexes or a unique constraint
if the field has ``db_index=True`` or ``unique=True``.
If the field is a ManyToManyField without a value for ``through``, instead of
creating a column, it will make a table to represent the relationship. If
If the field is a ``ManyToManyField`` without a value for ``through``, instead
of creating a column, it will make a table to represent the relationship. If
``through`` is provided, it is a no-op.
If the field is a ``ForeignKey``, this will also add the foreign key
constraint to the column.
remove_field
------------
::
remove_field(model, field)
.. method:: BaseDatabaseSchemaEditor.remove_field(model, field)
Removes the column(s) representing the field from the model's table, along
with any unique constraints, foreign key constraints, or indexes caused by
@@ -147,25 +128,22 @@ If the field is a ManyToManyField without a value for ``through``, it will
remove the table created to track the relationship. If
``through`` is provided, it is a no-op.
alter_field
------------
::
alter_field(model, old_field, new_field, strict=False)
.. method:: BaseDatabaseSchemaEditor.alter_field(model, old_field, new_field, strict=False)
This transforms the field on the model from the old field to the new one. This
includes changing the name of the column (the ``db_column`` attribute),
changing the type of the field (if the field class changes), changing
the ``NULL`` status of the field, adding or removing field-only unique
constraints and indexes, changing primary key, and changing the destination
of ForeignKey constraints.
includes changing the name of the column (the
:attr:`~django.db.models.Field.db_column` attribute), changing the type of the
field (if the field class changes), changing the ``NULL`` status of the field,
adding or removing field-only unique constraints and indexes, changing primary
key, and changing the destination of ``ForeignKey`` constraints.
The most common transformation this cannot do is transforming a
ManyToManyField into a normal Field or vice-versa; Django cannot do this
without losing data, and so it will refuse to do it. Instead, ``remove_field``
and ``add_field`` should be called separately.
``ManyToManyField`` into a normal Field or vice-versa; Django cannot do this
without losing data, and so it will refuse to do it. Instead,
:meth:`.remove_field` and :meth:`.add_field` should be called separately.
If the database has the ``supports_combined_alters``, Django will try and
do as many of these in a single database call as possible; otherwise, it will