Question

I have designed my database structure, like below to support the creation of multiple shops and users assigned to those shops. My tables use InnoDB storage engine.

[user]  
user_id 

[user_profile]  
user_profile_id  
user_id

[user_to_shop] PIVOT 
user_id  
shop_id

[shop]  
shop_id

[shop_profile]  
shop_profile_id  
shop_id  

[category_to_shop] PIVOT  
category_id  
shop_id

[category]  
category_id

[category_description]  
category_description_id  
category_id 

[product_to_category] PIVOT  
product_id
category_id

[product_to_shop] PIVOT
product_id
shop_id

[product]
product_id

...  
...

What I want to achieve is to delete all related records(category records, shop records, …, …) when a user(user_id) is deleted.

I have created constraints per entity. So when I remove a user_id(1), engine takes care of removing user_profile(user_id(1)) also.

ALTER TABLE `user_profile`
ADD CONSTRAINT `user_profile_cs1`
FOREIGN KEY (`user_id`) REFERENCES `user`(`user_id`)
ON DELETE CASCADE

But what should I do with pivot tables? How should I declare constraints or foreign keys on those tables to get the job done and be safe?

Answer 1

Create a chain of deletion: Add FK constraints to the pivot tables ([C]) or [D] that depends on C, below)

[A]
idA
dataA

[B]
idB
dataB

[C]
idC
idA
FOREIGN KEY (idA) REFERENCES A(idA)
ON DELETE CASCADE
idB
FOREIGN KEY (idB) REFERENCES B(idB)
ON DELETE CASCADE

[D]
idD
idC
FOREIGN KEY (idC) REFERENCES C(idC)
ON DELETE CASCADE

Order of operations

Delete(A) -> Delete(C) -> Delete(D)
Delete(B) -> Delete(C) -> Delete(D)