DRF. Trying to create a record that requires an instance of another DB object, and keep getting &quo-CodePudding

I'm new to Django and DRF and I'm really struggling with something.

I'm attempting to create a record in a table that has a foreign key. We'll say the models looks like this:

class Foo(models.Model):
  foo_id = models.IntegerField(
    primary_key=True,
  )
  name = models.CharField(
    max_length=256,
  )

class Bar(models.Model):
  bar_id = models.CharField(
    primary_key=True,
    max_length=256
  )
  name = models.CharField(
    max_length=256,
  )
  foo = models.ForeignKey(
    Foo,
    models.SET_NULL,
    related_name='rel',
  )

When I try this:

Bar.objects.create(
  bar_id = "A1",
  name = "John",
  foo = 5
)

I get the error that I would expect:

Cannot assign "5": "Bar.foo" must be a "Foo" instance.

But if I try:

Bar.objects.create(
  bar_id = "A1",
  name = "John",
  foo = Foo.objects.get(foo_id=7)
)

I get:

int() argument must be a string, a bytes-like object or a number, not 'Foo'

Really don't understand as I'm sure I've created records like this elsewhere.

CodePudding user response：

Try this:

Bar.objects.create(
  bar_id = "A1",
  name = "John",
  foo_id = 7
)

or this:

bar = Bar(bar_id="A1", name="John")
bar.foo_id = 7
bar.save()

CodePudding user response：

first you should null=True when you are using SET_NUll

   foo = models.ForeignKey(
    Foo,
    models.SET_NULL,
    null=True,
    related_name='rel',   )

Secound you can use below approaches

Bar.objects.create(
      bar_id = "A1",
      name = "John",
      foo_id = 5
    )

and your secound approach is correct

Bar.objects.create(
  bar_id = "A1",
  name = "John",
  foo = Foo.objects.get(foo_id=7)
)