django，表继承：插入数据

Question

I have these tables:

class OpeDatos(models.Model):
    id_dato = models.IntegerField(primary_key=True)
    id_usuario = models.ForeignKey(SisUsuarios, db_column='id_usuario')
    id_region = models.ForeignKey(SisRegiones, db_column='id_region')
    titulo = models.CharField(max_length=70, blank=True)
    class Meta:
        managed = False
        db_table = 'ope_datos'

class OpeProductos(OpeDatos):
    id_producto = models.IntegerField(primary_key=True)
    iddato = models.OneToOneField(OpeDatos, primary_key=True, db_column="id_dato",   parent_link=True)
    id_producto_tipo = models.ForeignKey(DefProductosTipos, db_column='id_producto_tipo')
    class Meta:
         managed = False
         db_table = 'ope_productos'

I want to insert data :

from apps.inicio.models import SisUsuarios, SisRegiones, OpeDatos

usuario = SisUsuarios.objects.get(pk=1)
region = SisRegiones.objects.get(pk=1)
datos = OpeDatos()
datos.id_usuario = usuario
datos.id_region = region     
datos.save()
producto = OpeProductos() 
producto.iddato = datos.id_dato
producto.save()

displays this message:

ValueError at /productos/add/

Cannot assign None: "OpeProductos.iddato" does not allow null values.

can you help me, please.

Answer 1

When creating an id manually you should use AutoField instead of IntegerField

id_dato = models.AutoField(primary_key=True)

https://docs.djangoproject.com/en/1.6/ref/models/fields/#autofield

What is happening is that since you are not explicitly defining the 'datos' object's id it doesnt have one, and then producto complains because the key can't have an empty value.

AutoField should fix this

Answer 2

I am surprised it doesn't fail at the earlier line: datos.save() because you have not supplied a value for the primary key datos.id_dato

Normally in Django you would need to use an AutoField to get an auto-incrementing primary key.

Also you should not be specifying primary_key=True on the OpeProductos.iddato field, you can only have one primary key per model.

Then the error you are seeing is due to the fact that datos.id_dato is None since you did not provide any value for it before saving the datos instance.