How do I validate wtforms fields against one another?

Question

I have three identical SelectField inputs in a form, each with the same set of options. I can\'t use one multiple select.

I want to make sure that the u

Answer 1

I wrote a small python library required to make cross-field validation like this easier. You can encode your validation logic declaratively as pairwise dependencies. So your form may look like:

from required import R, Requires, RequirementError

class MyForm(Form):

    VALIDATION = (
        Requires("select1", R("select1") != R("select2") +
        Requires("select2", R("select2") != R("select3") +
        Requires("select3", R("select3") != R("select1")
    )

    select1 = SelectField('Select 1', ...)
    select2 = SelectField('Select 2', ...)
    select3 = SelectField('Select 3', ...)

    def validate(self):
        data = {
            "select1": self.select1.data,
            "select2": self.select2.data,
            "select3": self.select3.data,
        }

        # you can catch the RequirementError
        # and append the error message to 
        # the form errors

        self.VALIDATION.validate(data)
        return result

You can take the VALIDATION object and append more validation rules or even put it in a separate module and import / reuse validation rules in different places.