Re: Change tracking API in Cayenne

Right. This was one of the options briefly mentioned on SO, and is *the* way to do it with the current public API. The downsides are of course forcing the user to deal with translation of names from DB space to object space, and the inability to track to-many relationship changes (which may not be always needed). 

Andrus

> On Oct 16, 2019, at 4:56 AM, Maik Musall <[email protected]> wrote:
> 
> Hi Andrus,
> 
> I had a way to do this when I migrated from EOF to Cayenne and needed to keep it. This is what I came up with at the time (uses Guava). It’s a method on my own DataObject subclass.
> 
> 	public Map<String,ValueDifference<Object>> changedAttributes() {
> 		Set<String> attributeKeys = new HashSet<>( attributeKeys() );
> 		Map<String,Object> dataRow = oc().getObjectStore().getSnapshot( getObjectId() );
> 		
> 		if( dataRow == null ) {	// newly inserted object
> 			dataRow = new HashMap<>();
> 			for( String key : attributeKeys ) {
> 				dataRow.put( key, null );
> 			}
> 		}
> 		
> 		Map<String,Object> committedValues = new HashMap<>();
> 		Map<String,Object> uncommittedValues = new HashMap<>();
> 		for( String key : dataRow.keySet() ) {
> 			if( !attributeKeys.contains( key ) ) continue;
> 			committedValues.put( key, dataRow.get( key ) );
> 			Object uncommittedValue = readPropertyDirectly( key );
> 			uncommittedValues.put( key, uncommittedValue );
> 		}
> 		
> 		MapDifference<String,Object> difference = Maps.difference( committedValues, uncommittedValues );
> 		Map<String,ValueDifference<Object>> entriesDiffering = difference.entriesDiffering();	 // assuming the all keys will always be present in both
> 		return entriesDiffering;
> 	}
> 
> Not really pretty, but works and doesn’t require reflection.
> 
> Maik
> 
> 
>> Am 11.10.2019 um 12:28 schrieb Andrus Adamchik <[email protected]>:
>> 
>> Was just answering Cayenne change tracking question on StackOverlow [1], and realized that the only user-friendly API that allows to check for individual changes is "cayenne-commitlog" that only works during commit. All the pre-commit APIs are internal and require lots of hoop jumping. I think we can address that on the cheap in 4.2 by defining a method like this in GraphManager.java:
>> 
>> GraphDiff getChanges();
>> 
>> We already have such method implemented in ObjectStore, so there's really no effort and an immediate benefit. Or take it a step further and additionally implement filtering changes per object:
>> 
>> GraphDiff getChanges(Persistent)
>> 
>> Thoughts?
>> 
>> Andrus
>> 
>> [1] https://stackoverflow.com/questions/58318730/what-is-the-current-best-method-of-getting-the-changes-to-an-object-hierarchy-in
>