django-richtemplates comes with some custom forms which are designed to be reusable and easily extensible. Here is a list of available forms:
This form allow us to choose a field on which other fields within same form would rely on when it comes to make a query.
Concept of this form is simple but let us start with some basics. Let’s assume we have one model which is heart of our scheme, and we have also 3 other models which are related to the first one:
class Project(models.Model): name = models.CharField(max_length=32) is_public = models.BooleanField(default=True) created_at = models.DateTimeField(auto_now_add=True) created_by = models.ForeignKey(User) class Task(models.Model): summary = models.CharField(max_length=64) content = models.TextField() project = models.ForeignKey(Project) status = models.ForeignKey('Status') priority = models.ForeignKey('Priority') created_at = models.DateTimeField(auto_now_add=True) author = models.ForeignKey(User) edited_at = models.DateTimeField(auto_now=True) editor = models.ForeignKey(User) class Status(models.Model): name = models.CharField(max_length=16) project = models.ForeignKey(Project) class Priority(models.Model): name = models.CharField(max_length=16) project = models.ForeignKey(Project)
Our object here is to create a form for the Task. We defined foreign key to the project table as we want to be able to specify other statuses and priorities for different projects. Normally we would create a form like this:
But with this approach our form would give us ability to choose status and priority from all possible objects, related to each project. So we need to override status and priority fields or create some factory method which would return us a TaskForm with status and priority fields limited to the previously chosen project. And what if we would have to make more such form classes? We do not want to break DRY rule, are we? Sure we don’t and LimitingModelForm is here for us! To make one we would simply add choices_limiting_fields option to our form’s Meta subclass:
LimitingModelForm directly extends django.forms.ModelForm class and at the time of initialization, after normal django.forms.ModelForm.__init__ logic it simply calls a method which limits already created fields with foreign key to the model we specify in choices_limiting_fields iterable.
This is still somewhat experimental and overall implementation should be improved.
Do not use this form in admin! It would work perfectly fine for existing Task objects but if you’d try to create new one from admin a LimitingModelFormError would be risen as LimitingModelForm requires that field specified in chocies_limiting_fields option is already set on the object. This should be fixed though.