NativeQuery Result Entity

Question

To make a join query of two or more tables from database I wrote a native query and execute that query.
Th entity manager is obtained from a container managed session facade.
The tables at database are like
table A(column1, column2, column3)
table B(column4, column5, column6)
the native query is like this
select a.column1 as c1,
a.column2 as c2,
a.column3 as c3,
b.column4 as c4,
b.column5 as c5,
b.column6 as c6
from A a, B b where a. column1 = b.column4
and the result entity class like this
public class JoinQueryResult{
private String c1;
private String c2;
private String c3;
private String c4;
private String c5;
private String c6;
// getters and setters here
and executing the query like
Query q = entityManager.createNativeQuery(sql,JoinQueryResult.class);
List<JoinQueryResult> = q.getResultList();
when I want to set c6 attribute of one instance of JoinQueryResult the entity manager automatically want to update the entity of JoinQueryResult and gets an error saying there is no table JoinQueryResult .
This is not the real table. I want just get the result of this join query to java beans.
What is the solution or best way to this method.
There must be way for example saying entity mnager do not persist this entity because it is just the result of native query.
Or could you plese say a solution method for this situation
best regards

Answer 1

Hello,
I can't say which is best, but there are a number of options.
You can either throw away the EntityManager or clear it once you've read your data (to make all the entities detached), or make all the fields in the Entity insertable=false, updatable=false ie:
@Entity
public class JoinQueryResult{
  @Column(insertable=false, updatable=false )
  private String c1;
}If you already have tables A and B mapped to Entities (say EntityA and EntityB) you can do the same thing in JPA but it won't require JoinQueryResult to be an entity - you can use a constructor in a jpa query. For instance:
createQuery("Select new package.JoinQueryResult( a.c1, a.c2, a.c3, b.c4, b.c5, c.c6) from EntityA a, EntityB b, where a.c1=b.c4");
The returned joinQueryResult objects would then not be managed, but it assumes you have Entities for the A and B tables, and that the JoinQueryResult has a constructor to take in all values.
Not related to getting readonly data, but you can also map the Entity in such a way to not require native queries, but having your JoinQueryResult map to tables A and B
@Table(name="A")
@SecondaryTable(name="B",
pkJoinColumns=@PrimaryKeyJoinColumn(name="column4"))
public class JoinQueryResult{
@Column(name="column1")
private String c1;