Composite column constraints

Is there any way to add constraints to column composites? For example, I'd like to impose a uniqueness constraint to a pair of columns directly in Beam. Should I just delegate this to raw SQL commands?

CREATE TABLE someTable (
id serial PRIMARY KEY,
col1 int NOT NULL,
col2 int NOT NULL,
UNIQUE (col1, col2)
)

I can get around it for now by making it a composite primary key, but I really don't want to do that.

Thanks