[1.8.x] Fixed #25371 -- Added reverse_sql and reverse_code examples to docs.

Backport of 4283a03843 from master
This commit is contained in:
Bibhas 2015-09-09 15:56:09 +05:30 committed by Tim Graham
parent ce3dd17c2e
commit 72219d7b32
1 changed files with 21 additions and 3 deletions

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@ -228,6 +228,14 @@ queries and parameters in the same way as :ref:`cursor.execute()
If you want to include literal percent signs in the query, you have to double
them if you are passing parameters.
The ``reverse_sql`` queries are executed when the migration is unapplied, so
you can reverse the changes done in the forwards queries::
migrations.RunSQL(
["INSERT INTO musician (name) VALUES (%s);", ['Reinhardt']],
["DELETE FROM musician where name=%s;", ['Reinhardt']],
)
The ``state_operations`` argument is so you can supply operations that are
equivalent to the SQL in terms of project state; for example, if you are
manually creating a column, you should pass in a list containing an ``AddField``
@ -274,6 +282,10 @@ match the operation's place in the project history, and the second is an
instance of :class:`SchemaEditor
<django.db.backends.base.schema.BaseDatabaseSchemaEditor>`.
The ``reverse_code`` argument is called when unapplying migrations. This
callable should undo what is done in the ``code`` callable so that the
migration is reversible.
The optional ``hints`` argument will be passed as ``**hints`` to the
:meth:`allow_migrate` method of database routers to assist them in making a
routing decision. See :ref:`topics-db-multi-db-hints` for more details on
@ -301,14 +313,20 @@ model::
Country(name="France", code="fr"),
])
def reverse_func(apps, schema_editor):
# forwards_func() creates two Country instances,
# so reverse_func() should delete them.
Country = apps.get_model("myapp", "Country")
db_alias = schema_editor.connection.alias
Country.objects.using(db_alias).filter(name="USA", code="us").delete()
Country.objects.using(db_alias).filter(name="France", code="fr").delete()
class Migration(migrations.Migration):
dependencies = []
operations = [
migrations.RunPython(
forwards_func,
),
migrations.RunPython(forwards_func, reverse_func),
]
This is generally the operation you would use to create