Skip a column on INSERT with JPA

I have a JPA/EclipseLink model with multiple parameters whose values are set as defaults by the PostgreSQL database. Specifically, I have:

An id column of type SERIAL which auto-increments when new rows are added
A created_at column of type TIMESTAMP which defaults to now()

My model looks like this:

import javax.persistence.*;

@Entity
@Table(name="entity")
@NamedQuery(name="Entity.findAll", query="SELECT e from Entity e")
public class Entity {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;

    @Column(name="created_at")
    private java.sql.Timestamp createdAt;

    // constructor, getters, and setters
}

When I try to insert a row with persist() in javax.persistence.EntityManager, the insertion fails because a NULL value is being set for the created_at column. Rather than inserting NULL, I want to simply not insert anything into that column and allow PostgreSQL to set it to now(). Essentially, I would like to use @GeneratedValue on createdAt, but that annotation is only for primary keys and cannot be used on multiple attributes. Is there another annotation I can use that will accomplish this?

Solution

You may want insertable=false in the Column annotation:

@Column(name="created_at", insertable=false)
private java.sql.Timestamp createdAt;

From: http://docs.oracle.com/javaee/5/api/javax/persistence/Column.html

boolean insertable (Optional) Whether the column is included in SQL INSERT statements generated by the persistence provide