-- Drop medium bindings and restore the original three-role constraint.
DELETE FROM photo_objects WHERE role = 'medium';

CREATE TABLE photo_objects_old (
    photo_id  TEXT NOT NULL REFERENCES photos(id) ON DELETE CASCADE,
    object_id TEXT NOT NULL REFERENCES objects(id) ON DELETE RESTRICT,
    role      TEXT NOT NULL CHECK (role IN ('original', 'thumb', 'preview')),
    PRIMARY KEY (photo_id, role)
);

INSERT INTO photo_objects_old (photo_id, object_id, role)
SELECT photo_id, object_id, role FROM photo_objects;

DROP TABLE photo_objects;

ALTER TABLE photo_objects_old RENAME TO photo_objects;

CREATE INDEX IF NOT EXISTS photo_objects_object_idx ON photo_objects (object_id);