From 9323f81dc03047371329c954c8eec8ef97d4dc16 Mon Sep 17 00:00:00 2001 From: Gabriel Hurley Date: Wed, 16 Feb 2011 00:18:09 +0000 Subject: [PATCH] Fixed #14820 -- Added more information to the generic relation docs regarding different choices for storing PK references for a GenericForeignKey. Thanks to mrmachine for the all the work on the patch. git-svn-id: http://code.djangoproject.com/svn/django/trunk@15545 bcc190cf-cafb-0310-a4f2-bffc1f526a37 --- docs/ref/contrib/contenttypes.txt | 32 ++++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-) diff --git a/docs/ref/contrib/contenttypes.txt b/docs/ref/contrib/contenttypes.txt index 18db29eefc..e232289385 100644 --- a/docs/ref/contrib/contenttypes.txt +++ b/docs/ref/contrib/contenttypes.txt @@ -251,13 +251,8 @@ model: 2. Give your model a field that can store primary key values from the models you'll be relating to. For most models, this means a - :class:`~django.db.models.PositiveIntegerField`. - - This field must be of the same type as the primary key of the models - that will be involved in the generic relation. For example, if you use - :class:`~django.db.models.fields.IntegerField`, you won't be able to - form a generic relation with a model that uses a - :class:`~django.db.models.fields.CharField` as a primary key. + :class:`~django.db.models.PositiveIntegerField`. The usual name + for this field is "object_id". 3. Give your model a :class:`~django.contrib.contenttypes.generic.GenericForeignKey`, and @@ -267,6 +262,29 @@ model: :class:`~django.contrib.contenttypes.generic.GenericForeignKey` will look for. +.. admonition:: Primary key type compatibility + + The "object_id" field doesn't have to be the same type as the + primary key fields on the related models, but their primary key values + must be coercible to the same type as the "object_id" field by its + :meth:`~django.db.models.Field.get_db_prep_value` method. + + For example, if you want to allow generic relations to models with either + :class:`~django.db.models.IntegerField` or + :class:`~django.db.models.CharField` primary key fields, you + can use :class:`~django.db.models.CharField` for the + "object_id" field on your model since integers can be coerced to + strings by :meth:`~django.db.models.Field.get_db_prep_value`. + + For maximum flexibility you can use a + :class:`~django.db.models.TextField` which doesn't have a + maximum length defined, however this may incur significant performance + penalties depending on your database backend. + + There is no one-size-fits-all solution for which field type is best. You + should evaluate the models you expect to be pointing to and determine + which solution will be most effective for your use case. + This will enable an API similar to the one used for a normal :class:`~django.db.models.ForeignKey`; each ``TaggedItem`` will have a ``content_object`` field that returns the