Auto context fields

The create, update and patch mutations contains a meta-field auto_context_fields. It allows us to automatically assign field values depending on values in the context (i.e. the current HttpRequest). Most typically, this will be used to automatically assign the the current user to some field.

Suppose for instance you have the following model:

class ForumThread(models.Model):
    created_by = models.ForeignKey(User, on_delete=models.CASCADE)

    # More fields

We can then automatically assign the created_by field to the calling user by creating a mutation:

class CreateForumThreadMutation(DjangoCreateMutation):
    class Meta:
        auto_context_fields = {
            'created_by': 'user'
        }

Presupposing, of course, that the user field of the info.context (HttpRequest) field is set. This works with any context field. Also note that auto context fields are automatically set as required=False, to please Graphene. Finally note that if we add an explicit value to the createdBy field when calling the mutation, this value will override the auto context field.