Re: Change tracking API in Cayenne

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