Properly deleting comments on a Post in JPA

Question

I have a front-end application with a JPA/JAX-RS backend, where i want to make a request to delete a comment on a post.

I'm using the repository pattern, where i have made the following method to delete a comment:

@Override
public Comment delete(Comment comment)
{
return getEntityManager().createQuery("DELETE Comment c WHERE c.id = :id ", Comment.class)
        .setParameter("id", comment.getId())
        .getSingleResult();
}

here i get the error:

Update/delete queries cannot be typed JPA

Here I'm a bit in doubt of what to do, i could just change the Comment.class and make it a generic query, but inside my facade, which calls the method

I also want to make a conditional check i there was a comment or not

 Comment commentToDelete = commentRepository.get(comment);
        if(commentToDelete == null){
            throw new ResourceNotFoundException(Comment.class, comment);
        }

how can i solve this problem in the easiest way, can i return an Object and just cast that, or is there another way to check for the comment and delete it from the database?

Alien · Answer 1 · 2018-12-04T12:38:47.987

1

You missed FROM in the query.

Change query to this DELETE FROM Comment c WHERE c.id = :id by specifying FROM

Refer this

edited Dec 04 '18 at 12:38

answered Dec 04 '18 at 12:17

Alien

15,141
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It still gives the same error, do i need to make it a generic query? – Kristoffer Tølbøll Dec 04 '18 at 12:18

score 1 · Answer 2 · answered Dec 04 '18 at 12:29

You can omit the conditional check because as per getSingleResult() documentation if there is no result it will throw NoResultException, you can just catch that exception and re-throw yours.

So solution would look something like this:

try {
    Comment deletedComment = commentRepository.delete(comment);
} catch (NoResultException nre) {
    throw new ResourceNotFoundException(Comment.class, comment)
}

Also make sure to add FROM to your JPQL query as Alien said.

Edit: I think you should call query.executeUpdate() rather than calling getSingleResult();

Mehdi · Accepted Answer · 2018-12-04T12:36:42.490

1

When you create a DELETE OR UPDATE query, you should always use executeUpdate method

getEntityManager().createQuery("DELETE FROM Comment c WHERE c.id = :id ", Comment.class)
        .setParameter("id", comment.getId())
        .executeUpdate();

The return type of this method is an integer telling you how many rows within your table have been affected

edited Dec 04 '18 at 12:36

answered Dec 04 '18 at 12:31

Mehdi

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Properly deleting comments on a Post in JPA

3 Answers3