=head2 add_unique_constraint
Declare a unique constraint on this source. Call once for each unique
-constraint. Unique constraints are used when you call C<find> on a
-L<DBIx::Class::ResultSet>. Only columns in the constraint are searched,
-for example:
+constraint.
# For UNIQUE (column1, column2)
__PACKAGE__->add_unique_constraint(
constraint_name => [ qw/column1 column2/ ],
);
+Unique constraints are used, for example, when you call
+L<DBIx::Class::ResultSet/find>. Only columns in the constraint are searched.
+
=cut
sub add_unique_constraint {