How to set a default property value with Hibernate

java

hibernate-defaults

column-definition

column-default

byNikita Barsukov·Dec 28, 2024

For a static default value, assign it directly to the field in your entity:

@Entity
public class MyEntity {
    private String propertyName = "defaultValue"; // Look ma, a default value
}

For dynamically computed defaults, use @PrePersist to initiate the value just before saving:

@Entity
public class MyEntity {
    private String propertyName;  // Going incognito for now!
    
    @PrePersist
    private void setDefaultValues() {
        propertyName = (propertyName == null) ? "Reddit loves cats" : propertyName;
    }
}

To record a timestamp default, delegate it to @CreationTimestamp:

@Entity
public class MyEntity {
    @CreationTimestamp
    private Date creationDate; // When were you born again?
}

Indulging in setting Hibernate defaults

The power of columnDefinition

To set default values at the database level, we resort to @Column and the omnipotent columnDefinition:

@Column(name = "status", nullable = false, columnDefinition = "VARCHAR(10) DEFAULT 'PENDING'")
private String status;

Remember to insure your code's portability; be conscious of the database-specific columnDefinition syntax.

Hibernate's pillar: columnDefault

Turn to @ColumnDefault for defining defaults at the Hibernate's layer :

@ColumnDefault("'New'")
private String status;

Don't forget to encourage Hibernate to regenerate the schema post this banner change.

The charm of dynamic-insert

Spare your database from lethargy by enabling dynamic-insert for frequent entity insertions coupled with null values:

<property name = "hibernate.use_sql_comments" value="true"/>

By giving null values a miss in its insert statements, dynamic-insert adds brownie points to your app.

Brewing defaults before persisting

In cases requiring runtime computation of defaults, @PrePersist comes to your rescue:

@PrePersist
public void prePersist() {
    status = (status == null) ? "Brewing coffee for you" : status; // Yes, we serve coffee!
}

Maintaining non-null fields as doctrine

Use @Column(nullable = false) to make sure the values are not left blank:

@Column(name = "email", nullable = false)
private String email;

This will urge users or devs to add marshmallows to the chocolate (Honestly, who likes chocolate without marshmallows?)

Jousting advanced scenarios with default values

Time-critical values? @CreationTimestamp dotes on setting default time:

@CreationTimestamp
private LocalDateTime createdAt;

Flyway lets you surf the waves of schema migrations with an even keel.

Got computed values to refresh upon retrieving your JPA entity after an insert action? @Generated(GenerationTime.INSERT) to the rescue.

The blend of simplicity and sophistication

Direct Java-based assignment of values

An upfront declaration of variable initialization is the simplest way to go:

private String status = "active"; // As active as a squirrel on a coffee drip!

A befriending complex calculations and Hibernate

Hibernate invites you to map complex calculations:

@Formula("subtotal * (1 - discount_rate)")
private BigDecimal totalValue;

Use @Formula for defaults based off other fields.

Preserving post-persist values

To maintain consistency of inserted values, a refresh could be needed:

@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@PostLoad
private void updateGeneratedValues() {
    // Refresh "instant coffee" post persistance to keep it hot, always!
}

More than a heads up oiling your Hibernate mechanics

Potential pitfalls with columnDefinition

Irrespective of the simplicity of columnDefinition, it's important to screen for potential issues with portability and migration. Keep your seatbelt fastened during database switches/upgrades.

Grains of salt with @ColumnDefault

Remember: @ColumnDefault doesn’t play fair when it comes to runtime schema changes; it merely assists Hibernate DDL generation tool. Brace yourself for defaults not setting on your pre-existing columns.

Post-persist freshness

The odor of freshness via @Generated is captivating. But be aware: depending on your configuration, manual refresh may be needed for the generated values to be applied correctly.

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