Last week I wrote about how you can create a Composite ID in Hibernate if your table has multiple key columns. In this post, I will show you how you can use a NamedQuery to select entities with embedded composite ids.
The code is shown below. The entity class is the same as before except for the @NamedQueries annotation which defines two named queries. The first query searches for a user with a specific first name and last name. The second query allows you to specify multiple last names in an "in-clause".
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Embeddable;
import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
/**
* The User entity which contains an embedded UserId.
*/
@Entity
@Table(name = "Users")
@NamedQueries({
@NamedQuery(name="user.findByName",
query = "from User where id.firstName = :firstName and id.lastName = :lastName"),
@NamedQuery(name="user.withLastNames",
query = "from User where id.lastName in (:lastName)")
})
public class User {
@EmbeddedId
private UserId id;
private String website;
@Temporal(TemporalType.TIMESTAMP)
@Column(insertable = false)
private Date lastUpdateTime;
/**
* Default constructor required by Hibernate.
*/
public User() {
}
/**
* This represents a "composite primary key" for the Users table.
* It contains all the columns that form a unique id.
* Must implement equals() and hashcode() and be serializable.
* https://community.jboss.org/wiki/EqualsAndHashCode
*/
@Embeddable
public static class UserId implements Serializable {
private static final long serialVersionUID = 1L;
private String firstName;
private String lastName;
/**
* Default constructor required by hibernate.
*/
public UserId() {
}
/** (non-Javadoc)
* @see java.lang.Object#hashCode()
*/
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((firstName == null) ? 0 : firstName.hashCode());
result = prime * result + ((lastName == null) ? 0 : lastName.hashCode());
return result;
}
/** (non-Javadoc)
* @see java.lang.Object#equals(java.lang.Object)
*/
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
UserId other = (UserId) obj;
if (firstName == null) {
if (other.firstName != null)
return false;
} else if (!firstName.equals(other.firstName))
return false;
if (lastName == null) {
if (other.lastName != null)
return false;
} else if (!lastName.equals(other.lastName))
return false;
return true;
}
}
}
Usage:
The code snippet below shows how you would use the named queries:
// the first query
Query query1 = entityManager.createNamedQuery("user.findByName")
.setParameter("firstName", "Peter")
.setParameter("lastName", "Griffin");
List<User> resultList = query1.getResultList();
// the second query
Query query2 = entityManager.createNamedQuery("user.withLastNames")
.setParameter("lastNames", Arrays.asList("Dent", "Griffin"));
List<User> resultList = query2.getResultList();
