Setting a JPA timestamp column to be generated by

问题:

In my SQL Server 2000 database, I have a timestamp (in function not in data type) column of type DATETIME named lastTouched set to getdate() as its default value/binding.

I am using the Netbeans 6.5 generated JPA entity classes, and have this in my code

@Basic(optional = false)
@Column(name = "LastTouched")
@Temporal(TemporalType.TIMESTAMP)
private Date lastTouched;

However when I try to put the object into the database I get,

javax.persistence.PersistenceException: org.hibernate.PropertyValueException: not-null property references a null or transient value: com.generic.Stuff.lastTouched

I've tried setting setting the @Basic to (optional = true), but that throws an exception saying the database doesn't allow null values for the TIMESTAMP column, which it doesn't by design.

ERROR JDBCExceptionReporter - Cannot insert the value NULL into column 'LastTouched', table 'DatabaseName.dbo.Stuff'; column does not allow nulls. INSERT fails.

I previously got this to work in pure Hibernate, but I have sense switched over to JPA and have no idea how to tell it that this column is suppose to be generated on the database side. Note that I am still using Hibernate as my JPA persistence layer.

回答1:

I fixed the issue by changing the code to

@Basic(optional = false)
@Column(name = "LastTouched", insertable = false, updatable = false)
@Temporal(TemporalType.TIMESTAMP)
private Date lastTouched;

So the timestamp column is ignored when generating SQL inserts. Not sure if this is the best way to go about this. Feedback is welcome.

回答2:

I realize this is a bit late, but I've had success with annotating a timestamp column with

@Column(name="timestamp", columnDefinition="TIMESTAMP DEFAULT CURRENT_TIMESTAMP")

This should also work with CURRENT_DATE and CURRENT_TIME. I'm using JPA/Hibernate with Oracle, so YMMV.

回答3:

I do not think that every database has auto-update timestamps (e.g. Postgres). So I've decided to update this field manually everywhere in my code. This will work with every database:

thingy.setLastTouched(new Date());
HibernateUtil.save(thingy);

There are reasons to use triggers, but for most projects, this is not one of them. Triggers dig you even deeper into a specific database implementation.

MySQL 5.6.28 (Ubuntu 15.10, OpenJDK 64-Bit 1.8.0_66) seems to be very forgiving, not requiring anything beyond

@Column(name="LastTouched")

MySQL 5.7.9 (CentOS 6, OpenJDK 64-Bit 1.8.0_72) only works with

@Column(name="LastTouched", insertable=false, updatable=false)

not:

FAILED: removing @Temporal
FAILED: @Column(name="LastTouched", nullable=true)
FAILED: @Column(name="LastTouched", columnDefinition="TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP")

My other system info (identical in both environments)

• hibernate-entitymanager 5.0.2
• hibernate-validator 5.2.2
• mysql-connector-java 5.1.38

回答4:

I have this working well using JPA2.0 and MySQL 5.5.10, for cases where I only care about the last time the row was modified. MySQL will create a timestamp on first insertion, and every time UPDATE is called on the row. (NOTE: this will be problematic if I cared whether or not the UPDATE actually made a change).

The "timestamp" column in this example is like a "last-touched" column.x`

The code below uses a separate column "version" for optimistic locking.

private long version;
private Date timeStamp

@Version
public long getVersion() {
    return version;
}

public void setVersion(long version) {
    this.version = version;
}

// columnDefinition could simply be = "TIMESTAMP", as the other settings are the MySQL default
@Column(name="timeStamp", columnDefinition="TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP")
@Temporal(TemporalType.TIMESTAMP)
public Date getTimeStamp() {
    return timeStamp;
}

public void setTimeStamp(Date timeStamp) {
    this.timeStamp = timeStamp;
}

(NOTE: @Version doesn't work on a MySQL "DATETIME" column, where the attribute type is "Date" in the Entity class. This was because Date was generating a value down to the millisecond, however MySQL was not storing the millisecond, so when it did a comparison between what was in the database, and the "attached" entity, it thought they had different version numbers)

From the MySQL manual regarding TIMESTAMP :

With neither DEFAULT nor ON UPDATE clauses, it is the same as DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP.

回答5:

@Column(nullable = false, updatable = false)
@CreationTimestamp
private Date created_at;

this worked for me. more info