Question

I have entity objects:

@Entity
public class Tag {

    @Id
    private Long id;

    @Transient
    private int count;

    // getter, setter etc..
}

@Entity
public class Request {

    // fileds

    @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Set<Tag> tag = new HashSet<Tag>();

    // getter, setter etc..
}

I need to get all tags with count by Request.

In DAO I make function for it with SQL query:

select tag as id, count(rt.request) as count
from request_tag rt
where rt.request in  (...) and rt.request in (...) and etc...
group by rt.tag order by count desc

Tags found but count isn’t binding.

How can I bind count from query?

PS:

1. I don’t want to remove @Transient annotation (because I don’t want keep count in DB).

2. I don’t want to use @Formula (because it will be slow).

Answer 1

Option 1:
Create named query with select tag as id, count(rt.request) as count, after execution you will get Object[2] cast as expected and use.

Option 2:
You can create yet another entity (saying TagStatistic) without @Transient
and map it to native(!) named query

@Entity
@Table(name = "Tag")//map to the same table
@NamedNativeQueries({
  @NamedNativeQuery(name ="TagStatistic.someName",
          resultClass =  TagStatistic.class,
          query = "select tag as id, count(rt.request) as count ....
...
public class TagStatistic{
...