Question

You would think that this would be an easy question to answer.

How do I, in Java, filter by an entity’s key (not a property that just happens to be of type Key, but its actual key – what we would call the “primary key” in relational database land)?

I don’t want to get a single entity with a particular key. I actually do want to do a filter and return a subset of the entities.

Answer 1

The trick is to use Entity.KEY_RESERVED_PROPERTY in place of property name:

Query q = new Query("MyEntity");
q.setFilter(new Query.FilterPredicate(Entity.KEY_RESERVED_PROPERTY, 
                Query.FilterOperator.GREATER_THAN,
                KeyFactory.createKey("MyEntity", "somevalue")));

This will find all MyEntity entities with key greater than somevalue.