Easily get a list of required fields of a Flask-SQLAlchemy model, i.e. where db.Column(..., nullable=False)

flask_sqlalchemy_required_fields.py

from flask_sqlalchemy import Model, SQLAlchemy
from sqlalchemy import inspect

# Extend the base Model, for more details see:
# https://flask-sqlalchemy.palletsprojects.com/en/2.x/customizing/#model-class
class ExtendedModel(Model):
    @classmethod
    def required_fields(cls) -> list:
        '''Returns column names for the Model where nullable=False'''
        mapper = inspect(cls)
        # Define column names that shouldn't appear in the final list
        not_required = {'id',}
        return [
            c.name
            for c in mapper.columns
            if not c.nullable and c.name not in not_required
        ]

db = SQLAlchemy(model_class=ExtendedModel)

class Item(db.Model):
    id = db.Column(db.Integer, primary_key=True) # Required by default
    name = db.Column(db.String(50), nullable=False) # Required
    description = db.Column(db.String(250)) # Not required
    
if __name__ == '__main__':
    # The printed list will only contain one item: ['name']
    print(Item.required_fields())