Question

In the following code example how do the user/userParam references relate to the Customer and Account lookups and what is the relationship between Customer and Account?

    // PersistenceManager pm = ...;
    Transaction tx = pm.currentTransaction();
    User user = userService.currentUser();
    List<Account> accounts = new ArrayList<Account>();

    try {
        tx.begin();

        Query query = pm.newQuery("select from Customer " +
                                  "where user == userParam " +
                                  "parameters User userParam");
        List<Customer> customers = (List<Customer>)
        query.execute(user);

        query = pm.newQuery("select from Account " +
                            "where parent-pk == keyParam " +
                            "parameters Key keyParam");
        for (Customer customer : customers) {
            accounts.addAll((List<Account>)
            query.execute(customer.key));
        }

    } finally {
        if (tx.isActive()) {
            tx.rollback();
        }
    }

Answer 1

The first query is querying all Customers where Customer.user == userParam. So it looks like Customers have a one-to-one relationship with Users (presumably this is the GAE User class).

The second query is querying all Accounts where the account’s parent-key is the key of a customer. So it looks like Customers have a parent-child relationship with Accounts.

Putting it all together, every User has one Customer, and every Customer can have multiple child Accounts. An Account can only have one parent Customer.