TransactionalIndexedCollection support for UniqueIndex is broken

[abhishek]

TransactionalIndexedCollection<Car> cache = new TransactionalIndexedCollection<>(Car.class);
cache.addIndex(UniqueIndex.onAttribute(Car.CAR_ID));
cache.add(new Car(1, "Ferrari"));

cache.update(Collections.singletonList(new Car(1, "Ferrari")), Collections.singletonList(new Car(1, "Mercedes")));

I expected this to succeed since I am basically trying to update CAR_ID = 1 with new data.

However I get - UniqueConstraintViolatedException

com.googlecode.cqengine.index.unique.UniqueIndex$UniqueConstraintViolatedException: The application has attempted to add a duplicate object to the UniqueIndex on attribute 'carId', potentially causing inconsistencies between indexes. UniqueIndex should not be used with attributes which do not uniquely identify objects. Problematic attribute value: '1', problematic duplicate object: Car[carId=1, name='Mercedes']

Looking at

cqengine/code/src/main/java/com/googlecode/cqengine/TransactionalIndexedCollection.java

Lines 248 to 263 in a0fb1bf

	if (objectsToAddIterator.hasNext()) {
	// Configure new reading threads to exclude the objects we will add,
	// and then wait for threads reading previous versions to finish...
	incrementVersion(objectsToAdd);
	// Now add the given objects...
	modified = doAddAll(objectsToAdd, queryOptions);
	}
	if (objectsToRemoveIterator.hasNext()) {
	// Configure (or reconfigure) new reading threads to (instead) exclude the objects we will remove,
	// and then wait for threads reading previous versions to finish...
	incrementVersion(objectsToRemove);
	// Now remove the given objects...
	modified = doRemoveAll(objectsToRemove, queryOptions) || modified;
	}

If we move DELETE before ADD, unique index would work.

I don't fully understand exclusion logic and I can see some interaction due to remove before add for new readers.

If, that's the case. Then updating the documentation/code to block UniqueIndex and TransactionalIndexedCollection being used together.