What does ": P" mean in a JDO request

Question

I am using JDO in a Google app. Each “Employee” has a “key”. I have a set of keys and you want to get all the employees whose key belongs to this set.

So, I implemented it using the filter 'contains ()', as indicated here . The code works fine and looks like this:

List<Key> keys = getLookupKeys(....) ..//Get keys from somewhere.

Query query = pm.newQuery(Employee.class,":p.contains(key)"); //What is ":P" here?
List<Employee> employees = (List<Employee>) q.execute(keys); //This correctly gives me all I want

All that interests me is what is this ": P" in this query? The Employee object does not have a field named 'p', nor does my request declare any such parameter. So what does this mean? Does p have any special meaning?

Answer 1

, . , setParameter, . , , :

Query query = pm.newQuery(Employee.class,":keys.contains(key)");
List<Employee> employees = (List<Employee>) q.execute(keys); 

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. " " Apache JDOQL docs.