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glindholm
 Post subject: Mutable Date's and dirty checking
PostPosted: Wed Oct 20, 2004 2:18 pm 
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Joined: Tue Sep 21, 2004 4:04 pm
Posts: 25
Location: Oldsmar, FL
Hibernate version:2.1.6

Since Java Date's are mutable we want to ensure that our objects are never sharing Date objects so we've always written out Date property setters like this:

Code:
    public void setLastUpdated(Date lastUpdated)
    {
        this.lastUpdated = new Date(lastUpdated.getTime());
    }


This seems to cause hibernate to believe the object is dirty and need to be updated. (The object that it sets is not the object it gets back.)

Is there a way to tell hibernate check dirty on a Date by value with an equals() instead of by object id?
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steve
 Post subject:
PostPosted: Thu Oct 21, 2004 11:39 am 
Hibernate Team
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Joined: Tue Aug 26, 2003 3:00 pm
Posts: 1816
Location: Austin, TX
Hibernate's built-in date types do all perform comparison by value already. Have a look at DateType and TimestampType in the net.sf.hibernate.type package.

More than likely you might have a problem with precision or something similiar.
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steve
 Post subject:
PostPosted: Thu Oct 21, 2004 11:42 am 
Hibernate Team
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Joined: Tue Aug 26, 2003 3:00 pm
Posts: 1816
Location: Austin, TX
for illustration, consider:
Code:
      Date nowD = new Date();

      Timestamp nowTS = new Timestamp( nowD.getTime() );
      nowTS.setNanos(234);


      try {
         System.out.println("     Using Date.equals() : " + nowD.equals(nowTS));
         System.out.println("Using Timestamp.equals() : " + nowTS.equals(nowD));

         System.out.println("----------------------------------");

         System.out.println("Using ts-type, from date : " + Hibernate.TIMESTAMP.equals(nowD, nowTS) );
         System.out.println("  Using ts-type, from ts : " + Hibernate.TIMESTAMP.equals(nowTS, nowD) );

         System.out.println("----------------------------------");

         System.out.println("Using date-type, from date : " + Hibernate.DATE.equals(nowD, nowTS) );
         System.out.println("  Using date-type, from ts : " + Hibernate.DATE.equals(nowTS, nowD) );
      }
      catch(HibernateException e)
      {}


Which outputs:
Code:
     Using Date.equals() : false
Using Timestamp.equals() : false
----------------------------------
Using ts-type, from date : false
  Using ts-type, from ts : false
----------------------------------
Using date-type, from date : true
  Using date-type, from ts : true
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glindholm
 Post subject:
PostPosted: Thu Oct 21, 2004 12:07 pm 
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Joined: Tue Sep 21, 2004 4:04 pm
Posts: 25
Location: Oldsmar, FL
Ok, here is what I'm seeing.

Here is the mapping for this property (generated by xdoclet).

Code:
        <property
            name="lastUpdated"
            type="timestamp"
            update="true"
            insert="true"
            access="property"
            column="lastUpdated"
            not-null="true"
        />


here is the full code (it's a java.util.Date):

Code:
    private Date   lastUpdated = new Date();

    /**
     * @hibernate.property
     * type = "timestamp" 
     * not-null = "true"
     */
    public Date getLastUpdated()
    {
        return lastUpdated;
    }

    public void setLastUpdated(Date lastUpdated)
    {
        this.lastUpdated = new Date(lastUpdated.getTime());
    }


If I retrieve this object in a new session (not the one it was saved in) and I don't modify it, Hibernate is (incorrectly) issuing an UPDATE when I commit the transaction.

If I change the setter like the following then there is no UPDATE (as expected).

Code:
    public void setLastUpdated(Date lastUpdated)
    {
        this.lastUpdated = lastUpdate;
    }


That's the only change I make.

The UPDATE should not be happening.
I'm I doing something wrong?
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steve
 Post subject:
PostPosted: Thu Oct 21, 2004 1:51 pm 
Hibernate Team
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Joined: Tue Aug 26, 2003 3:00 pm
Posts: 1816
Location: Austin, TX
Well, have you manually done the comparisons yourself using the TimestampType? Or better yet, debugged by setting a break-point at TimestampType.equals()?
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glindholm
 Post subject:
PostPosted: Fri Oct 22, 2004 11:17 am 
Beginner
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Joined: Tue Sep 21, 2004 4:04 pm
Posts: 25
Location: Oldsmar, FL
Ok I ran it thru the debugger and I think I found a bug.

Here is the TimestampType.equals() code and I've annotated it with the debug values as comments.

It looks like Timestamp objects are getting there nano values added twice.

Code:

//net.sf.hibernate.type.TimestampType

   public boolean equals(Object x, Object y) {

// x = Date
//       fasttime = 1098456751887
// y = Timestamp
//       fasttime = 1098456751000
//       nanos = 887000000
      
      if (x==y) return true;
      if (x==null || y==null) return false;
      
      long xTime = ( (java.util.Date) x ).getTime();
// xTime = 1098456751887
      long yTime = ( (java.util.Date) y ).getTime();
// yTime = 1098456751887
//*** xTime == yTime and both have nano values set
      boolean xts = x instanceof Timestamp;
// xts = false
      boolean yts = y instanceof Timestamp;
// yts = true
      int xNanos = xts ? ( (Timestamp) x ).getNanos() : 0;
// xNanos= 0
      int yNanos = yts ? ( (Timestamp) y ).getNanos() : 0;
// yNanos= 887000000
      xTime += xNanos / 1000000;
// xTime= 1098456751887
      yTime += yNanos / 1000000;
// yTime= 1098456752774
// *** I think this is the bug: yTime already had the nanos and they are being added again.

      if ( xTime!=yTime ) return false;
      if (xts && yts) {
         // both are Timestamps
         int xn = xNanos % 1000000;
         int yn = yNanos % 1000000;
         return xn==yn;
      }
      else {
         // at least one is a plain old Date
         return true;
      }
      
   }


Java: Sun's j2sdk1.4.2_01 on Windows XP
Hibernate 2.1.6
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glindholm
 Post subject:
PostPosted: Fri Oct 22, 2004 11:23 am 
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Joined: Tue Sep 21, 2004 4:04 pm
Posts: 25
Location: Oldsmar, FL
Correction: I said nanos above but I guess it's really the milliseconds that are being added twice.
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glindholm
 Post subject:
PostPosted: Fri Oct 22, 2004 2:21 pm 
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Joined: Tue Sep 21, 2004 4:04 pm
Posts: 25
Location: Oldsmar, FL
I took a look into CVS and the TimestampType has been changed since the Hibernate 2.1.6 release (rev 1.11).

The current code (rev 1.13) looks like this.

Code:
      if ( !Environment.jvmHasJDK14Timestamp() ) {
         xTime += xNanos / 1000000;
         yTime += yNanos / 1000000;
      }
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