I'm very interested in the idea of expanding the database level
constraints that can be supplied to a database schema, and also
automatically apply the same constraints to the model/view in django.
The various backends that support them, I believe already apply such
constraints for PositiveIntegerField() and so on.
I would like to see the ability to define extra constraints as part of
the model definition, and have these applied in a similar manner to
the unique and unique_together constraints.
I am more familiar with PostgreSQL than anything else, but I believe
the syntax I am about to propose will work in several databases.
Check constraints can be divided into two types: column level and
table level. With PostgreSQL, a column level constraint can reference
another column, but I would suggest that a constraint that does so
should be a table level constraint.
Column level constraints could be declared as a keyword argument to
the field constructor:
column = models.IntegerField(constraint='< 100')
Table level constraints could be declared as an attribute on the Meta
class of the model:
check_constraints = ('start < finish', )
Validation of the models should pick up when an incorrect constraint
has been declared. For instance, not using a valid operator ('# 100')
or not supplying a valid comparison value ('< 1e' for an IntegerField)
would be invalid column constraints, and comparing a Date to an
Integer would be an invalid table level constraint.
The code that should be generated would add "CHECK ('column' < 100)"
to the column definition in the first instance, and "CONSTRAINT
app_table_start_finish CHECK ('start' < 'finish')" to the table
definition in the second case.
I have already written code that fulfils these requirements, and some
tests for validation errors. I have also written additions to
BaseModelForm which validates according to the defined constraint(s).
At this stage, I have not allowed for more complicated relationships,
such as ('first < second + 65'), but this is planned.
Is there anyone else interested in this? Should I put this into a
ticket and attach my current diff?
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Django developers" group.
To post to this group, send email to django-developers@googlegroups.com
To unsubscribe from this group, send email to
django-developers+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/django-developers?hl=en
-~----------~----~----~----~------~----~------~--~---
