Setting default values for columns in JPA

You can do the following:

@Column(name="price")
private double price = 0.0;

There! You've just used zero as the default value.

Note this will serve you if you're only accessing the database from this application. If other applications also use the database, then you should make this check from the database using Cameron's columnDefinition annotation attribute, or some other way.

In 2017, JPA 2.1 still has only @Column(columnDefinition='...') to which you put the literal SQL definition of the column. Which is quite unflexible and forces you to also declare the other aspects like type, short-circuiting the JPA implementation's view on that matter.

Hibernate though, has this:

@Column(length = 4096, nullable = false)
@org.hibernate.annotations.ColumnDefault("")
private String description;

Identifies the DEFAULT value to apply to the associated column via DDL.

• Hibernate 4.3 docs (4.3 to show it's been here for quite some time)
• Hibernate manual on Default value for database column

Two notes to that:

1) Don't be afraid of going non-standard. Working as a JBoss developer, I've seen quite some specification processes. The specification is basically the baseline that the big players in given field are willing to commit to support for the next decade or so. It's true for security, for messaging, ORM is no difference (although JPA covers quite a lot). My experience as a developer is that in a complex application, sooner or later you will need a non-standard API anyway. And @ColumnDefault is an example when it outweigts the negatives of using a non-standard solution.

2) It's nice how everyone waves @PrePersist or constructor member initialization. But that's NOT the same. How about bulk SQL updates? How about statements that don't set the column? DEFAULT has it's role and that's not substitutable by initializing a Java class member.

another approach is using javax.persistence.PrePersist

@PrePersist
void preInsert() {
   if (this.createdTime == null)
       this.createdTime = new Date();
}

Actually it is possible in JPA, although a little bit of a hack using the columnDefinition property of the @Column annotation, for example:

@Column(name="Price", columnDefinition="Decimal(10,2) default '100.00'")