Polymorphic Association Example

polymorphic.sql

CREATE TABLE linkable (
    id            serial PRIMARY KEY
);

CREATE TABLE obja (
    id            integer not null,
    name          varchar(50) NOT NULL,
    FOREIGN KEY(id) REFERENCES linkable(id)
);

CREATE TABLE objb (
    id            integer not null,
    name          varchar(50) NOT NULL,
    FOREIGN KEY(id) REFERENCES linkable(id)
);

CREATE TABLE carousel_item (
    id                 serial PRIMARY KEY,
    name                varchar(50),
    linkable_id     integer not null,
    FOREIGN KEY(id) REFERENCES linkable(id)
);

insert into linkable (id) values (1), (2), (3), (4);
insert into obja (id, name) values (1, 'obj 1'), (2, 'obj 2');
insert into objb (id, name) values (3, 'obj 3'), (4, 'obj 4');

insert into carousel_item (id, name, linkable_id)
values
    (1, 'carousel item 1', 1),
    (2, 'carousel item 2', 3),
    (3, 'carousel item 3', 2),
    (4, 'carousel item 4', 4);

select * from carousel_item
left join obja on linkable_id=obja.id
left join objb on linkable_id=objb.id;