belongs_to

Many-to-one — the foreign key lives on this (owning) table, pointing at the target table.

#[repository(table = "completed_challenge")]
#[belongs_to(table = "challenge")]
pub trait CompletedChallengeRepository: Repository {
    // challenge_uuid → JOIN "challenge" ON "challenge".id = "completed_challenge".challenge_id
    //                   WHERE "challenge".uuid = $1 AND user_id = $2 LIMIT 1
    async fn first_by_challenge_uuid_and_user_id(
        &self, challenge_uuid: Uuid, user_id: i32,
    ) -> sqlx::Result<Option<CompletedChallengeRow>>;

    // FK shortcut, no JOIN — challenge_id is the belongs_to FK column itself
    async fn first_by_challenge_id(&self, challenge_id: i32) -> sqlx::Result<Option<CompletedChallengeRow>>;
}

{table}_id (here, challenge_id) is the one column every relation kind has a no-JOIN shortcut for — since belongs_to's whole premise is that the FK already lives on this table, {table}_id resolves straight to that FK column instead of triggering a JOIN. Any other {table}_{col} (challenge_uuid above) does JOIN.

See relations for the full attribute table and defaults.