如果删除了孩子，则自动删除父母

Question

This my database relationship.

I got data like this:

LikeDislike
|-------------|--------------|-----------------|
|      id     |     userId   |    createdAt    |
|-------------|--------------|-----------------|
|       1     |       1      |    2019-03-26   |
|-------------|--------------|-----------------|

RoomLikes
|------------------|--------------|
|   likeDislikeId  |     roomId   | 
|------------------|--------------|
|       1          |       1      |
|------------------|--------------|

I want to do:

1. When I delete a data from RoomLikes , like DELETE FROM roomlikes where id = 1
2. The data in LikeDislike that related with RoomLikes will be deleted automatically.

Is there are ways to delete data of parent automatically if data of child was deleted?

Please let me know if you need more info.

Thanks.

Answer 1

If I understand the question you need to look into using a join in your delete statement - something like this:

DELETE RoomLikes, LikeDislike
FROM RoomLikes
INNER JOIN LikeDislike ON RoomLikes.likeDislikeId = LikeDislike.id
WHERE roomlikes.id=1;

Answer 2

You can use following queries

ALTER TABLE RoomLikes add foreign key (likeDislikeId) references LikeDislike(id) ON DELETE CASCADE;

Just remember that you need to have primary key in the referenced table (LikeDislike) to add foreign key. By using this, if you delete data on parent table, data of child table will be deleted.

Answer 3

Is it correct that a record in LikeDislike has exactly 1 child record that is either a RoomLike or a CommentLike ?

In that case you might consider altering the corresponding foreign keys with ON DELETE CASCADE and most of all, deleting the parent record instead of the child record.