Resolving ON DELETE CASCADE in many-to-many relation - postgresql

Question

See: SQLFiddle
I am having a many-to-many relationship as such:
CREATE TABLE IF NOT EXISTS store (
id BIGSERIAL PRIMARY KEY
);
CREATE TABLE IF NOT EXISTS collection (
id BIGSERIAL PRIMARY KEY,
store_id bigint NOT NULL,
FOREIGN KEY (store_id) REFERENCES store (id)
ON UPDATE CASCADE
);
CREATE TABLE IF NOT EXISTS item (
id BIGSERIAL PRIMARY KEY,
store_id bigint NOT NULL,
FOREIGN KEY (store_id) REFERENCES store (id)
ON UPDATE CASCADE
);
CREATE TABLE IF NOT EXISTS collection_item (
id BIGSERIAL PRIMARY KEY,
collection_id bigint NOT NULL,
item_id bigint,
UNIQUE (collection_id, item_id),
FOREIGN KEY (collection_id) REFERENCES collection (id)
ON DELETE CASCADE,
FOREIGN KEY (item_id) REFERENCES item (id)
ON DELETE SET NULL
);
INSERT INTO store (id) VALUES (1);
INSERT INTO item (id, store_id) VALUES (1, 1);
INSERT INTO collection (id, store_id) VALUES (1, 1);
INSERT INTO collection_item (id, collection_id, item_id) VALUES (DEFAULT, 1, 1);
My problem is that deleting a store
DELETE FROM store WHERE store.id = 1;
will give the following error:
ERROR: update or delete on table "store" violates foreign key constraint
"collection_store_id_fkey" on table "collection"
Detail: Key (id)=(1) is still referenced from table "collection".
I understand the problem but I don't know how I can resolve this issue.
If an item gets deleted, the relation in collection_item should not be removed but the item_id should be set to NULL. On the other hand, if a collection gets deleted, all related collection_item records should be removed as well.
How can DELETE CASCADE work in such a setup or do I have to model my tables differently if I need this kind of behavior?

Answer 1

You can just add ON DELETE CASCADE where you have ON UPDATE CASCADE
CREATE TABLE IF NOT EXISTS collection (
id BIGSERIAL PRIMARY KEY,
store_id bigint NOT NULL,
FOREIGN KEY (store_id) REFERENCES store (id)
ON UPDATE CASCADE
ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS item (
id BIGSERIAL PRIMARY KEY,
store_id bigint NOT NULL,
FOREIGN KEY (store_id) REFERENCES store (id)
ON UPDATE CASCADE
ON DELETE CASCADE
);
SQLFiddle

Answer 2

To resolve this issue you can add ON DELETE behavior to the store_id column of the collection table (and that of the item table). Basically you can just change the ON UPDATE to ON DELETE in both of these table definitions, since I doubt you'll be updating the id column for existing rows in the store table. You also mention the ON DELETE behavior for the item_id column of collection_item, if you want the column value to become NULL when an item is deleted, you can use ON DELETE SET NULL.
CREATE TABLE IF NOT EXISTS store (
id BIGSERIAL PRIMARY KEY
);
CREATE TABLE IF NOT EXISTS collection (
id BIGSERIAL PRIMARY KEY,
store_id bigint NOT NULL,
FOREIGN KEY (store_id) REFERENCES store (id)
ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS item (
id BIGSERIAL PRIMARY KEY,
store_id bigint NOT NULL,
FOREIGN KEY (store_id) REFERENCES store (id)
ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS collection_item (
id BIGSERIAL PRIMARY KEY,
collection_id bigint NOT NULL,
item_id bigint NOT NULL,
UNIQUE (collection_id, item_id),
FOREIGN KEY (collection_id) REFERENCES collection (id)
ON DELETE CASCADE,
FOREIGN KEY (item_id) REFERENCES item (id)
ON DELETE SET NULL
);

Answer 3

On this case, you have to delete table refrences before to delete stores id.
Or to do the modifications above.
DELETE FROM item where store_id= 1;
DELETE FROM collection where store_id = 1;
DELETE FROM store where id = 1;