please add min_length to django.db.models.fields.Field

[anonymous]

Use case is that an application may have requirements for a CharField to always have a minimum of N characters (e.g. git commit sha1 needs 40characters); but the application may not use forms. Validators for min_length and max_length could move from the forms.fields to models.fields.

​https://docs.djangoproject.com/en/dev/ref/forms/fields/#charfield

[Damien Nozay]

edge case: syncdb command can inspect the fields and see that min_length== max_length and mysql backend could use CHAR(N) instead of VARCHAR(N) which results in less bytes being consumed, which could be important savings with lots of records.

see ​https://github.com/django/django/pull/2921.

[Tim Graham]

If we added min_length to model fields, I'd think it should be enforced at the database level. Do all of the core databases support minimum length validation? (my guess is no.) In that case, it may be better to solve your use case (Python level validation) by adding a MinLengthValidator() to your field.

[Damien Nozay]

do all of the core databases support maximum length validation?

[Simon Charette]

I think only SQLite doesn't enforce them.

[Tim Graham]

I think it could be implemented in PostgreSQL using a CHECK constraint, but MySQL doesn't enforce them.