gistfile1.pyw

def create_preview_model(cls):
    "Create a preview model for a PreviewModel"
    name = cls.__name__ + "Preview"

    #Set up a dictionary to simulate declarations within a class
    attrs = {
        '__module__': cls.__module__,
    }
    
    #OneToOne to the model we are previewing
    attrs['preview_parent'] = models.OneToOneField(cls, related_name='preview')

    attrs['__str__'] = preview_string

    #duplicate all fields into this class, set your dependencies if any
    cls.dependencies = []
    for field in cls._meta.fields:
        if field.name != "preview_state":
            if isinstance(field, (ForeignKey, OneToOneField, ManyToManyField)):
                field_class = type(field)
                rel = field.rel
                
                field_dict = { "unique": field.unique,
                               "null": field.null,
                               "blank": field.blank
                               }
                if rel.related_name:
                    field_dict["related_name"] = "preview" + rel.related_name

                attrs[field.name] = field_class(rel.to, **field_dict)

                #if the dependency is a PreviewModel we will notify it of the model's current status
                dependency_fields = [f.name for f in rel.to._meta.fields]
                is_required = not field.blank and (not field.null or isinstance(field, ManyToManyField))
                if "preview_state" in dependency_fields and is_required:
                    cls.dependencies.append(field.name)
            else:
                attrs[field.name] = field

    #create the new class and set it on the PreviewModel class for later access
    new_class = type(name, (models.Model,), attrs)
    cls.preview_class = new_class
    return new_class