New attribute for tables that allow deleting #47
Description
Foreign keys to tables that allow deleting should have an index.
This is important to make deleting efficient.
Note that this is already implied by #[no_reference], maybe the new attribute should be #[no_reference(without_index)]
We could rename:
#[delete]#[no_reference]=>#[delete(no_reference)]
Either the index is added automatically, or the user needs to add the #[index] attribute.
Having the manual annotation makes it more clear which indices exist and can be used.