It looks like the 'default' parameter of a models.ForeignKey? field requires one to pass an id, passing an instance doesn't work. This is rather contra-intuitive as setting a ForeignKey? field of an instance of a model to an instance of the foreign model is supported.
Here's a sample:
#Models
class Foo(models.Model):
a = models.CharField(max_length=10)
def get_foo():
return Foo.objects.get(id=1)
class Bar(models.Model):
b = models.CharField(max_length=10)
a = models.ForeignKey(Foo, default=get_foo)
#Testing
In [8]: f = Foo(a='abc')
In [9]: f.save()
# Forgot to do a print here, but f.id == 1
In [10]: b = Bar(b='def')
In [11]: b.a = f
# Works fine, as expected
In [12]: b.save()
In [13]: b.a
Out[13]: <Foo: Foo object>
In [14]: c = Bar(b='ghi')
# Using 'default', callable returns f, doesn't work, unlike expected
In [15]: c.save()
---------------------------------------------------------------------------
pysqlite2.dbapi2.InterfaceError Traceback (most recent call last)
/home/nicolas/Projects/django/app/<ipython console>
/home/nicolas/Projects/django/django-trunk/django/db/models/base.py in save(self, raw)
259 cursor.execute("INSERT INTO %s (%s) VALUES (%s)" % \
260 (qn(self._meta.db_table), ','.join(field_names),
--> 261 ','.join(placeholders)), db_values)
262 else:
263 # Create a new record with defaults for everything.
/home/nicolas/Projects/django/django-trunk/django/db/backends/util.py in execute(self, sql, params)
16 start = time()
17 try:
---> 18 return self.cursor.execute(sql, params)
19 finally:
20 stop = time()
/home/nicolas/Projects/django/django-trunk/django/db/backends/sqlite3/base.py in execute(self, query, params)
131 def execute(self, query, params=()):
132 query = self.convert_query(query, len(params))
--> 133 return Database.Cursor.execute(self, query, params)
134
135 def executemany(self, query, param_list):
InterfaceError: Error binding parameter 1 - probably unsupported type.
Running this same query in a web view shows 'params' is [id, <Foo instance>], where the second expected value should be the id of the used Foo instance.
