Is there a way to pre-define built-in validators that can be used multiple times?

[herkalurk]

I'm working on an API based flask app with flask-smorest and marshmallow validations. The issue I'm running into, is that many api endpoints require the same type of data, and I don't want to continually copy/paste the same validations over and over. Something like below would happen....

from marshmallow import Schema, fields, validate

class api1():

	class input1(Schema):
		request_number = fields.Str(metadata={'description': 'Request Number', 'example':'REQUEST12345'}, validate=validate.Regexp(regex=r"^REQUEST\d{3,9}$", error="Input string didn't match required format - REQUEST12345"))	
		
class api2():

	class input1(Schema):
		request_number = fields.Str(metadata={'description': 'Request Number', 'example':'REQUEST12345'}, validate=validate.Regexp(regex=r"^REQUEST\d{3,9}$", error="Input string didn't match required format - REQUEST12345"))		

What I want to do is create some sort of function or class BEFORE I define every api field/schema that I could recall.

Below is the idea, though I don't believe it works.

from marshmallow import Schema, fields, validate

class repetative_validators():
	request_number = validate.Regexp(regex=r"^REQUEST\d{3,9}$", error="Input string didn't match required format - REQUEST12345"))

class api1():

	class input1(Schema):
		request_number = fields.Str(metadata={'description': 'Request Number', 'example':'REQUEST12345'}, validate=repetative_validators().request_number)
		
class api2():

	class input1(Schema):
		request_number = fields.Str(metadata={'description': 'Request Number', 'example':'REQUEST12345'}, validate=repetative_validators().request_number)	

I was able to successfully test creating my own function for validation as described here, but was hoping to use the built in validators.

from marshmallow import Schema, fields, validate, ValidationError
import re

def validate_request_number(value):
	if not re.match(r"^REQUEST\d{3,9}$"):
		raise ValidationError("Input string didn't match required format - REQUEST12345")
		
class api1():

	class input1(Schema):
		request_number = fields.Str(metadata={'description': 'Request Number', 'example':'REQUEST12345'}, validate=validate_request_number)
		
class api2():

	class input1(Schema):
		request_number = fields.Str(metadata={'description': 'Request Number', 'example':'REQUEST12345'}, validate=validate_request_number)		

If anyone can link to appropriate documentation or an example that would be helpful. I haven't found anything like this in the marshmallow docs yet

[lafrech]

You could subclass a field, something along those lines:

class RequestNumber(ma.fields.String):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, metadata={'description': 'Request Number', 'example':'REQUEST12345'}, validate=validate.Regexp(regex=r"^REQUEST\d{3,9}$", error="Input string didn't match required format - REQUEST12345")), **kwargs)


class Api1():

	class Input1(Schema):
		request_number = RequestNumber()

You could also subclass the base schema:

class RequestNumberSchema(ma.Schema):
    request_number = fields.Str(metadata={'description': 'Request Number', 'example':'REQUEST12345'}, validate=validate_request_number)


class Api1():

	class Input1(RequestNumberSchema):
            """Input schema with request number field"""
            ...  # Add other fields here

[herkalurk]

@lafrech Thanks for those examples. The first one seems to align more with what I'm trying to accomplish. I need to test to confirm my suspicion that those will translate uniform when I auto generate the swagger page showing the description and example for our users.