Django 联合主键 HELP

[delikely]

    title = models.CharField(max_length=200)
    ISBN = models.CharField(max_length=50,primary_key=True)
    author = models.CharField(max_length=80)
    press = models.CharField(max_length=100)
    category = models.CharField(max_length=30,primary_key=True)
    series = models.CharField(max_length=50,null=True)

    class Meta:
        unique_together = ('ISBN','category')

需要实现 ISBN+category 唯一，但是我发现插入第二条就报错了

2017-12-01 22:05:04] [19] [SQLITE_CONSTRAINT_PRIMARYKEY]  A PRIMARY KEY constraint failed (UNIQUE constraint failed: coding_book.category)

是我这样写不对吗，望各位指教。需要怎么写？

[yaoht]

ISBN = models.CharField(max_length=50,primary_key=True)
category = models.CharField(max_length=30,primary_key=True)

这两个都有 primary_key=True， 也就是说他们各自都必须 unique
并不是你想要的 MultipleColumnPrimaryKeys
https://code.djangoproject.com/wiki/MultipleColumnPrimaryKeys

[gaolycn]

unique_together = (('ISBN','category'),)

[jimzhong]

Django 尚未支持复合主键，https://code.djangoproject.com/wiki/MultipleColumnPrimaryKeys
我会使用 Django 自动创建的 id 主键，然后加上 unique 约束：
```python
title = models.CharField(max_length=200)
ISBN = models.CharField(max_length=50)
author = models.CharField(max_length=80)
press = models.CharField(max_length=100)
category = models.CharField(max_length=30)
series = models.CharField(max_length=50,null=True)

class Meta:
unique_together = ('ISBN','category')
```

@gaolycn 并不需要这么写，https://docs.djangoproject.com/en/1.11/ref/models/options/#unique-together

[gaolycn]

@jimzhong 果然。Django 细节处理的挺好。