CsvTextField

[AlexCLeduc]

For single-choices fields, we typically use CharField with the choices kwarg. Sometimes there are good reasons to make these foreign-keys to a lookup table, but hard-coded choices are typically easier and much faster to put together.

It would be nice if we could do the same with multiple-choice fields, in other words replacing many-to-many fields. What I'm thinking is:

• CsvTextField model field
  • the choices API would fit the regular char/text/int field choices API
  • my_record.mycsvfield would return an array of choice strings, not the raw delimited string stored in the DB, and my_record.get_mycsvfield_display() would return comma-separated formatted choices
  • Delimeter is |. There shouldn't be need for custom delimeters because choices are stored as codes, not formatted strings
  • basic model (but not DB) validation: choices conform to delimited choices
  • (extra) Maybe an option to use a backing CharField if we want a character limit? (Defaulting to Textfield seems safer)
• corresponding CsvField form field
• default widget of multi-select or checkbox-select

The main advantages here are

• ability to update choices without messing with the database
• ability to upgrade an existing single-choice CharField to a multi-choice CharField
• Much more productive for building stuff quickly

A few challenges I could think of are:

• Subclassing fields and overriding (de-)serialization seems kind of complicated
• The CSV field must contain at most one of each choice
• Should it validate that all value exist in the choices list? Migrations could be difficult if we don't allow this. On the other hand it's asking for problems if we don't
• Choices must be sorted in the same order all the time, otherwise we risk extraneous diffs
• Not sure how we map our fields to custom form fields without using a modelform subclass (with its own custom metaclass 🤮 ), might just have to manually set the field on each form that uses this type of field

[AlexCLeduc]

Ok this turned out to be simpler than I thought, we have a prototype in catalogue, if we don't run into issues I will add it to this package