Flask Framework Cookbook - Second Edition

How to do it...

In our catalog application, we used SelectField for category, and we populated the values for this field in our create_product() method on a GET request. It would be much more convenient if we did not concern ourselves with this and the population of this field was taken care of by itself.

Now, let's implement a custom field to do this in models.py:

class CategoryField(SelectField): 
 
    def iter_choices(self): 
        categories = [(c.id, c.name) for c in            Category.query.all()] 
        for value, label in categories: 
            yield (value, label, self.coerce(value) == self.data) 
 
    def pre_validate(self, form): 
        for v, _ in [(c.id, c.name) for c in  Category.query.all()]: if self.data == v: break else: raise ValueError(self.gettext('Not a valid choice')) ...