[FIXED] Can I use Form inheritance for only some fields? Validation error

Issue

I have one Parent form, and 2 Children forms, than inherit from it -

class ParentForm(FlaskForm):
    number_a = StringField('A',
                           validators=[DataRequired()],
                           render_kw={"placeholder":"A", 'class_':'input', 'id':'number_a'})
    number_b = StringField('B',
                           validators=[DataRequired()],
                           render_kw={"placeholder":"B", 'class_':'input', 'id':'number_b'})

class Child1Form(ParentForm):
    number_c = StringField('C',
                           validators=[DataRequired()],
                           render_kw={"placeholder":"C", 'class_':'input', 'id':'number_c'})

class Child2Form(ParentForm):
    number_d = StringField('D',
                           validators=[DataRequired()],
                           render_kw={"placeholder":"D", 'class_':'input', 'id':'number_d'})

For Child1Form I need number_a, number_b and number_c.

For Child2Form I need number_b and number_d, but I do not need number_a, so I don't submit it. This results in Validation error when I post the Child2Form, since in the ParentForm field is required.

How should I tackle this? Basically on certain forms I need to Validate the number_a field, on others I need to ignore it. But I don't want to type it multiple times, as I will potentially have a very large amount of forms.

Hopefully I got my point across, let me know if this is not the case.

Solution

This just sounds like the design problem in OOP of the "refused bequest". Something a child shouldn't do.

You should just arrange the inheritance hierarchy to cater for the needs of the child classes:

class ParentForm_B(FlaskForm):
    number_b = ...

class ParentForm(ParentForm_B):
    number_a = ...

class Child1Form(ParentForm):
    number_c = ...

class Child2Form(ParentForm_B):
    number_d = ...

Answered By - quamrana