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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/topics/db/models.txt | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/docs/topics/db/models.txt b/docs/topics/db/models.txt index 0c87cdc9d1..469733a3b6 100644 --- a/docs/topics/db/models.txt +++ b/docs/topics/db/models.txt @@ -1006,3 +1006,32 @@ field or method to every class that inherits the mix-in. Try to keep your inheritance hierarchies as simple and straightforward as possible so that you won't have to struggle to work out where a particular piece of information is coming from. + +Field name "hiding" is not permitted +------------------------------------- + +In normal Python class inheritance, it is permissible for a child class to +override any attribute from the parent class. In Django, this is not permitted +for attributes that are :class:`~django.db.models.fields.Field` instances (at +least, not at the moment). If a base class has a field called ``author``, you +cannot create another model field called ``author`` in any class that inherits +from that base class. + +Overriding fields in a parent model leads to difficulties in areas such as +initialising new instances (specifying which field is being intialised in +``Model.__init__``) and serialization. These are features which normal Python +class inheritance doesn't have to deal with in quite the same way, so the +difference between Django model inheritance and Python class inheritance isn't +merely arbitrary. + +This restriction only applies to attributes which are +:class:`~django.db.models.fields.Field` instances. Normal Python attributes +can be overridden if you wish. It also only applies to the name of the +attribute as Python sees it: if you are manually specifying the database +column name, you can have the same column name appearing in both a child and +an ancestor model for multi-table inheritance (they are columns in two +different database tables). + +Django will raise a ``FieldError`` exception if you override any model field +in any ancestor model. + |