Question

Here is my simplified database:

user_post
- id
- post_id (FK)

post
- id
- link_id (FK)

link
- id

I’ve a list of user_post and I wanna get for each of them the link they are linked to.

Currently, I’m doin it like this:

SELECT userPost.post.link FROM UserPost userPost WHERE userPost IN (:userPosts)

Works great, but maybe later, I’ll get a huge number of user_post, so there’ll be a lot of values within the IN clause (100 < x < 5000+).

Is IN limited? Is there any other way to do it? Before, I was doin it like this:

for (UserPost userPost : user.getUserPosts()) {
    Link link = userPost.getPost().getLink();
    //
}

But the solution above takes really a lot of time to get executed, so I’m lookin for a more optimized one.

Answer 1

Yes, the IN clause is limited:

The number of values in the IN list is only limited by the
max_allowed_packet value.

In Oracle, the limit is set to 1000 elements.

Instead of selecting user posts, and then iterating through them to get their link or issuing another query to get them, you could load the links in the same query as the user posts:

select userPost from UserPost userPost
left join fetch userPost.post post
left join fetch post.link link;

This query will load eveything at once, and iterating theough the user posts and getting their link using userPost.getPost().getLink() won’t trigger any additional query.