127 / 478
self.assertEqual(first_saved_item.list, list_)
AttributeError: 'Item' object has no attribute 'list'
A Foreign Key Relationship
How do we give our
Item
a list attribute? Let’s just try naively making it like the
text
attribute:
lists/models.py.
from
django.db
import
models
class
List
(
models
.
Model
):
pass
class
Item
(
models
.
Model
):
text
=
models
.
TextField
(
default
=
''
)
list
=
models
.
TextField
(
default
=
''
)
As usual, the tests tell us we need a migration:
$
python3 manage.py test lists
[...]
django.db.utils.OperationalError: table lists_item has no column named list
$
python3 manage.py makemigrations
Migrations for 'lists':
0004_item_list.py:
- Add field list to item
Let’s see what that gives us:
AssertionError: 'List object' != <List: List object>
We’re not quite there. Look closely at each side of the
!=
. Django has only saved the
string representation of the
List
object. To save the relationship to the object itself, we
tell Django about the relationship between the two classes using a
ForeignKey
:
lists/models.py.
from
django.db
import
models
class
List
(
models
.
Model
):
pass
class
Item
(
models
.
Model
):
text
=
models
.
TextField
(
default
=
''
)
list
=
models
.
ForeignKey
(
List
,
default
=
None
)
That’ll need amigration too. Since the last onewas a red herring, let’s delete it and replace
it with a new one:
$
rm lists/migrations/0004_item_list.py
$
python3 manage.py makemigrations
Migrations for 'lists':
Adjusting Our Models
|
99