Proposal to have sqlc generate string constants for constraints

[andrewmbenton]

I have some code that looks like:

obj, err = queries.SomeQuery()
if err != nil {
	var pgErr *pgconn.PgError
	if errors.As(err, &pgErr) && pgErr.ConstraintName == "some_unique_key" {
		// Let user know about constraint violation
		return
	}
	// Log query failure and return 500
	return
}

It would be nice if I had string constants for all of my constraint names to compare against, and I think sqlc should be capable of building that for me.

[rhodeon]

I agree this would be a great feature for sqlc to have.
I currently handle this by storing relevant constraints in a contraints.go file under my database directory, like so:

package postgres

const (
	// UNIQUE KEYS
	UniqueUsersId                    = "users_id_key"
	UniqueGroupId                    = "group_id_key"
	UniqueUsersToGroupsUserIdGroupId = "users_to_groups_user_id_group_id_key"

	// FOREIGN KEYS
	FKeyUsersToGroupsUserId  = "users_to_groups_user_id_fkey"
	FKeyUsersToGroupsGroupId = "users_to_groups_group_id_fkey"
)

Of course, this takes manual effort and isn't foolproof. Having sqlc generate the exhaustive set of available constraints (with commented metadata) if possible would be a massive boon.

If this gets implemented, it would be a good idea to have #835 in mind, as constraints are general to a database and can be centralised in a single file (or package) rather than being repeated per-model.