Reuse wtforms field in multiple forms

Question

I have a bunch of forms that have similar fields. To simplify my code, I'd like to define the fields outside of the forms and then add the fields to the forms as needed like this:

name = wt.StringField("name")
age = wt.StringField("age")

class Form1(FlaskForm):
    name=name

class Form2(FlaskForm):
    age=age

class Form3(FlaskForm):
    name=name
    age=age

This pattern seems to work, but I've never seen anyone do this before so I want to make sure that there are not edge cases where this will break. If so, are there better ways of doing this?

minou · Accepted Answer · 2021-04-27 14:26:11Z

2

Although the pattern in my question works, I'm nervous about using it since it doesn't appear to be a recommended way of doing things. This is a safer approach that meets my needs:

def name_field(): return wt.StringField("name")
def age_field(): return wt.StringField("age")

class Form1(FlaskForm):
    name=name_field()

class Form2(FlaskForm):
    age=age_field()

class Form3(FlaskForm):
    name=name_field()
    age=age_field()

answered Apr 27, 2021 at 14:26

minou

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1 Comment

0xed Over a year ago

what if i want to add a new validator in this case. Exp in Form3 add a custum name validator

minou · Accepted Answer · 2021-04-29 00:02:41Z

0

It seems to me FormField is what you're looking for.

class nameForm(Form):
    name = wt.StringField("name")


class ageForm(Form):
    age = wt.StringField("age")


class Form1(FlaskForm):
    name = FormField(nameForm)


class Form2(FlaskForm):
    age = FormField(ageForm)


class Form3(FlaskForm):
    name = FormField(nameForm)
    age = FormField(ageForm)

Here's some relevant documentation -> https://wtforms.readthedocs.io/en/2.3.x/fields/

Search this doc for the Field Enclosures Section

edited Apr 29, 2021 at 0:02

minou

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answered Apr 27, 2021 at 14:12

Andrew Clark

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3 Comments

minou Over a year ago

You could also do it without FormField like this class Form1(nameForm): pass. That is what I was doing before but I like the solution in my answer better.

Andrew Clark Over a year ago

@gaefan that's a neat way of doing it. I've done similar things for validating or populating forms but I did not realize you could call functions returning the actual Form Field. Cool solution!

Al Martins Over a year ago

Best documentation for FlaskForm. One parameter is missing though: choices. Maybe more

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