I thought I know how to use JOIN
in JPQL
but apparently not. Can anyone help me?
select b.fname, b.lname from Users b JOIN Groups c where c.groupName = :groupName
This give me Exception
org.eclipse.persistence.exceptions.JPQLException
Exception Description: Syntax error parsing the query
Internal Exception: org.eclipse.persistence.internal.libraries.antlr.runtime.EarlyExitException
Users
have a OneToMany relationship with Groups
.
Users.java
@Entity
public class Users implements Serializable{
@OneToMany(mappedBy="user", cascade=CascadeType.ALL)
List<Groups> groups = null;
}
Groups.java
@Entity
public class Groups implements Serializable {
@ManyToOne
@JoinColumn(name="USERID")
private Users user;
}
My second question is let say this query return a unique result, then if I do
String temp = (String) em.createNamedQuery("***")
.setParameter("groupName", groupName)
.getSingleResult();
***
represent the query name above. So does fname
and lname
concatenated together inside temp
or I get a List<String>
back?
Join on one-to-many relation in JPQL looks as follows:
select b.fname, b.lname from Users b JOIN b.groups c where c.groupName = :groupName
When several properties are specified in select
clause, result is returned as Object[]
:
Object[] temp = (Object[]) em.createNamedQuery("...")
.setParameter("groupName", groupName)
.getSingleResult();
String fname = (String) temp[0];
String lname = (String) temp[1];
By the way, why your entities are named in plural form, it's confusing. If you want to have table names in plural, you may use @Table
to specify the table name for the entity explicitly, so it doesn't interfere with reserved words:
@Entity @Table(name = "Users")
public class User implements Serializable { ... }