Hi,
I am trying to get to grips with persisting objects to the google
datastore, I have been following the Google tutorial.
So the following code uses the PersistnaceManager to save an Employee
instance:
Employee employee = new Employee("Alfred", "Smith", new Date());
PersistenceManager pm = PMF.get().getPersistenceManager();
try {
pm.makePersistent(employee);
} finally {
pm.close();
}
}
The Employee instance has an Id property:
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Long id;
So when the pm.makePersistent(employee); is called the id is
autogenerated.
This I understand. But my question is how do I fetch it back from the
datastore if I do not know what the id is? In the tutorials it shows
how you fetch objects using known information:
Key k = KeyFactory.createKey(Employee.class.getSimpleName(),
"[email protected]");
Employee e = pm.getObjectById(Employee.class, k);
But of course when you want to fetch a list of saved objects you will
not know any of the key information???
Or am I misunderstanding how this works?
In basic terms I want to save a list of Employee objects and then I
want to get them back without having to know the information they
contain...
Thanks
Luca
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