ON UPDATE CURRENT_TIMESTAMP and JPA

I have an entity with fields

@Temporal(TemporalType.TIMESTAMP)
@Column(name = "edit_timestamp", 
        columnDefinition="TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP")
private Date editTimestamp;

@Version
@Column(name = "edit_count")
private short editCount;

private String text;

When I try to update with Spring-Data-JPA, I observe edit开发者_Go百科_count has been incremented, but edit_timestamp still remain the same. If I manually invoke SQL

UPDATE post SET TEXT='456' WHERE post_id=1;

the edit_timestamp is updated. If I add

@PreUpdate
protected void onUpdate() {
    editTimestamp = new Date();
}

it works w/o issue. My question is why w/o @PreUpdate the edit_timestamp is not updated?

You need to change the column annotation to include updatable = false. This will cause the edit_timestamp column to not show up in the update SQL, so the JPA provider won't include the current value of the field which is what is causing it to override the default.

@Temporal(TemporalType.TIMESTAMP)
@Column(name = "edit_timestamp", 
        updatable = false,
        columnDefinition="TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP")
private Date editTimestamp;

You can mark the variables as update or creation timestamps in your entity. In the following example you can see how this can be done very easily using hibernate annotations:

@UpdateTimestamp
private LocalDateTime editTimestamp;

@CreationTimestamp
private LocalDateTime creationTimestamp;

Just for the reference and to make sure there is no confusion, I am using the following package imports for the respective datatypes and annotations:

import org.hibernate.annotations.CreationTimestamp
import org.hibernate.annotations.UpdateTimestamp
import java.time.LocalDateTime

Because in your initial set of annotations, all you've told it about the edit_timestamp column is that it is a timestamp; JPA doesn't know that it needs to update it. I'm guessing that when you're manually executing the SQL statement, you have some sort of on-update trigger that's changing those fields for you - but are being overwritten by the data coming from the persisted entity when you update it.
If you don't need the 'edited' count/timestamp, try removing them from the entity, and see if that works. Otherwise, you have a working solution.