“ city_id”列中的空值违反了非空约束

Question

This error happens when I tried to use Django admin to add a new entry in the database. This error shows even I tried to add a new state. What's wrong with my model?

class City(models.Model):
    city_id = models.AutoField(primary_key=True)
    city = models.CharField(max_length=100, blank=True, null=True)
    state = models.ForeignKey('State', models.DO_NOTHING, blank=True, null=True)

    class Meta:
        managed = False
        db_table = 'city'

    def __str__(self):
        return self.city

class State(models.Model):
    state_id = models.AutoField(primary_key=True)
    state = models.CharField(max_length = 10, blank=True, null=True)

    class Meta:
        managed = False
        db_table = 'state'

    def __str__(self):
        return self.state

Answer 1

Just found out the problem: It's a problem with my PostgreSQL database. This error shows even when I run INSERT in the database. So the problem is because my PRIMARY KEY is not a SERIAL value, rather, it's an INTEGER , thus it cannot auto increment when I insert a new value.

To solve this problem:

1. Delete the old integer id as well as all the foreign key constraint on it.
2. ALTER TABLE city ADD COLUMN city_id SERIAL PRIMARY KEY
3. Reconnect tables with new foreign keys

After that, my problem is solved. Hope this helps other people facing a similar problem!