Question

I’d like to fetch data from a table ordered by priority column that is enum. We use javaee 6, GF 3.1.

Our entity looks like this

@Entity
@Table(name="ITEMS")
@NamedQueries({
    @NamedQuery(
        name = "Item.findbyPriority",
        query = "select i from Item i where ORDER BY i.priority DESC" )
})
public class Item implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Integer id;



    String data inputFile;


    @Enumerated(EnumType.ORDINAL)
    Priority priority;


...
}

Priority is defined

public enum Priority {

    HIGH,
    NORMAL;
}

However Item.findbyPriority query sorts by ordinal, and returns result in wrong order. If I change Priority class to

public enum Priority {

        NORMAL,
        HIGH;
    }

It works OK. But that is not really robust. What if I add new Priority use or reorder it?

I tried to override compareTo method but it is final in Enum class.

What can I do in this case? How can it be done in nice way?

I know I could store priority as number etc, but than I have to sync entities to Enum by hand, which is not super nice.
Maybe @PrePersist, @PreUpldate and @PostLoad methods are the way to go? How would then jpql query look like?

thanks,

milan

Answer 1

Only way how you can affect order of priority outside of your named query is choosing type of enum attribute (ORDINAL, STRING).

Even if overriding compareTo would be aloud, it does not change a thing, because it is not called when query is executed. Reason for this is that JPQL query is converted to the SQL query, and there is no concept of calling Java methods from SQL query.

Also specifying callback methods does not help, because they to not have anything to do with generating query or affecting order of result list.

What you can do is to have post processing method that defines order for your list and just call that after you have results from executing named query.