15

私は 2 つのクラスを持っています。一方は他方から派生しています。同じ基本クラスから派生した両方の兄弟クラスを作成したいと考えています。

前：

from django.db import models

class A(models.Model):
    name = models.CharField(max_length=10)

class B(models.Model):
    title = models.CharField(max_length=10)

後：

from django.db import models

class Base(models.Model):
    name = models.CharField(max_length=10)

class A(Base):
    pass

class B(Base):
    title = models.CharField(max_length=10)

スキーマの移行を生成すると、質問に対する回答を含む出力が次のようになります。

+ Added model basetest.Base
? The field 'B.a_ptr' does not have a default specified, yet is NOT NULL.
? Since you are removing this field, you MUST specify a default
? value to use for existing rows. Would you like to:
?  1. Quit now, and add a default to the field in models.py
?  2. Specify a one-off value to use for existing columns now
?  3. Disable the backwards migration by raising an exception.
? Please select a choice: 3
- Deleted field a_ptr on basetest.B
? The field 'B.base_ptr' does not have a default specified, yet is NOT NULL.
? Since you are adding this field, you MUST specify a default
? value to use for existing rows. Would you like to:
?  1. Quit now, and add a default to the field in models.py
?  2. Specify a one-off value to use for existing columns now
? Please select a choice: 2
? Please enter Python code for your one-off default value.
? The datetime module is available, so you can do e.g. datetime.date.today()
>>> 37
+ Added field base_ptr on basetest.B
? The field 'A.id' does not have a default specified, yet is NOT NULL.
? Since you are removing this field, you MUST specify a default
? value to use for existing rows. Would you like to:
?  1. Quit now, and add a default to the field in models.py
?  2. Specify a one-off value to use for existing columns now
?  3. Disable the backwards migration by raising an exception.
? Please select a choice: 3
- Deleted field id on basetest.A
? The field 'A.name' does not have a default specified, yet is NOT NULL.
? Since you are removing this field, you MUST specify a default
? value to use for existing rows. Would you like to:
?  1. Quit now, and add a default to the field in models.py
?  2. Specify a one-off value to use for existing columns now
?  3. Disable the backwards migration by raising an exception.
? Please select a choice: 3
- Deleted field name on basetest.A
? The field 'A.base_ptr' does not have a default specified, yet is NOT NULL.
? Since you are adding this field, you MUST specify a default
? value to use for existing rows. Would you like to:
?  1. Quit now, and add a default to the field in models.py
?  2. Specify a one-off value to use for existing columns now
? Please select a choice: 2
? Please enter Python code for your one-off default value.
? The datetime module is available, so you can do e.g. datetime.date.today()
>>> 73
+ Added field base_ptr on basetest.A
Created 0002_auto__add_base__del_field_b_a_ptr__add_field_b_base_ptr__del_field_a_i.py. You can now apply this migration with: ./manage.py migrate basetest

B.base_ptr と A.base_ptr のデフォルト値に関する質問にどう答えたらよいかわかりません。定数を指定すると、実行時に移行が失敗し、次の出力が表示されます。

FATAL ERROR - The following SQL query failed: CREATE TABLE "_south_new_basetest_a" ()
The error was: near ")": syntax error
RuntimeError: Cannot reverse this migration. 'B.a_ptr' and its values cannot be restored.

ちなみにこれがsqlite3を使った結果です。Postgres を使用すると、次のようになります。

FATAL ERROR - The following SQL query failed: ALTER TABLE "basetest_a" ADD COLUMN "base_ptr_id" integer NOT NULL PRIMARY KEY DEFAULT 73;
The error was: could not create unique index "basetest_a_pkey"
DETAIL:  Key (base_ptr_id)=(73) is duplicated.

Error in migration: basetest:0002_auto__add_base__del_field_b_a_ptr__add_field_b_base_ptr__del_field_a_i
IntegrityError: could not create unique index "basetest_a_pkey"
DETAIL:  Key (base_ptr_id)=(73) is duplicated.

この移行を機能させるには、base_ptr にどの値を使用すればよいですか? ありがとう！

4

3 に答える 3

16

が単独でインスタンス化されない場合は、 prop tobaseを使用して問題を簡単に解決できます。abstract = Trueclass Meta

コード例:

from django.db import models

class Base(models.Model):
    name = models.CharField(max_length=10)
    class Meta:
        abstract = True

class A(Base):
    pass

class B(Base):
    title = models.CharField(max_length=10)
于 2016-09-16T20:43:09.440 に答える