Forms

A checklist on how to use a Django Form. It's purpose (as we use it) is to sanitize and coerce input data received from a user to a consistent format based on which we can perform custom actions (overwritting the save() method to send a registration email) or create or update model instances (ModelForm use case).

Prerequisities

• Introduction to forms (you can skip anything pertaining to form templates)
• Creating model instances based on model forms (pay close attention to the save, is_valid and errors section)
• Form validations (understand cleaning a specific attribute and validating fields that depend on each other)
• Model full_clean method

Checklist

Define fields

1. Does the field has the appropriate data type? Always verify available form field's data types
2. Have you checked all available form field options and see if they apply?
   • Is the field required?
3. Did you define class Meta options?
   • Should we not update any of the fields of a form (eg for a ModelForm) from user data? Ex: Let A be a Model with created_at set to auto_add_now. We should exclude the field from being set by user data using Meta.exclude (or using Meta.fields), otherwise the user might set a date in the past

Define validations

1. Can we use default field validators?
   • Use clean_fieldname to provide custom validation yielding a ValidationError in a false case
   • Use clean_a_field_and_b_field to clean dependent fields and overwrite Form.clean() to call upon this method
2. What could a user do (send as values) to screw us over? This is just a thought to always keep in mind when working with user data!

Define action

1. Overwrite save() method to perform actions using sanitized data provided in self.cleaned_data or to update the form's instance object

TODO: Use case for collapsing form field values into an instance's value

Pitfalls

1. A field's initial option isn't equivalent to setting the default value of the field