opal.core.fields module contains helper functions for working
with fields, as well as custom Opal field definitions.
A helper function that returns true if a field is numeric. For our purposes, Integers, Decimals, BigIntegers, Floats and Positive Integers are considered numeric.
is_numeric(models.IntegerField()) # -> True
A helper function that returns a Django choices definition from star args.
enum('one', '2', 'III') # -> ( # ('one', 'one'), # ('2', '2'), # ('III', 'III') # )
A field that stores it's value as a generic foreign key to an Opal LookupList or as the value in a CharField.