django many2many field make not required

I created a form based on a model. The model has a 开发者_Python百科many2many field. I defined the field like this:

contacts = models.ManyToManyField(Contact, blank=True, null=True)

I`m wondering now why the generated form says that this field cannot be blank. I always get the error message "This field is required.", when i do not select a contact for the contacts field.

Whats`s wrong?

In your form declaration mark this field as required=False

class MyForm(forms.ModelForm):
  contacts=forms.ModelMultipleChoiceField(queryset=Contact.objects.all(),required=False)
  class Meta:
    model=MyModel

Possibly you did syncdb before adding blank=True, null=True?

syncdb will only create tables if they don't exist in the database. Changes to models have to be done manually in the database directly with SQL or using a migration tool such as South.

Of course, if you are still in early development, it will be easier to drop the database and run syncdb again.

Your use of null=True is confusing here. A manyToMany field results in a 3rd table relating one model to another. e.g.

Business <-> Contact

If business.contacts is empty, no records are entered into this table. null=True would make me think you are intending for NULL records to be added to this table, which doesn't seem valid.

Typically you would leave both of these attributes off.