Once again,
I'm not saying we should support constraints WITHIN the model.
Let me state my assumptions:
- validations exist to give users a nice error message to prevent
models from being saved, because otherwise, the database will raise a
nasty error
- validations do not validate 100%
- constraints validate 100%
- constraints cannot be defined in model, they must be defined when
defining tables
- preventing from within Ruby code & rollbacks from database both have
same results -- NO CHANGE.
- constraints raise ugly exceptions
- validations give nice error messages
So I'm suggesting that we should have a feature for models to RESCUE
(catch) the exception raised by the database connection and turn it
into a nice error message, like what validations do.
database_validates_constraint would not tell the database to actually
implement the constraint (because that's done when defining tables)
but would CATCH a constraint error thrown by the database and
translate that into a nice error message, like what validations do.
Example:
# table definition
DB.create_table :items do
...
constraint price_is_positive {:price > 0}
...
end
# model
database_validates_constraint 'price_is_positive', :msg => "Price
must be positive!"
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