Google App Engine Java and searches on Entities

Question

I'm developing a web application with GAE Java. I created the entity Repair and LineRepair in this way:

public static void createOrUpdateRiparazione(Key key, String plate,
        String mechanicname, String type, String km, String description,
        String date, String price, String qta) {
    Transaction txn = Util.getDatastoreServiceInstance().beginTransaction();

    try {

        Entity repair = new Entity("Repair", key);
        repair.setProperty("plate", plate);
        repair.setProperty("date", date);
        repair.setProperty("status", "Created");
        repair.setProperty("km", km);
        repair.setProperty("mechanic", mechanicname);
        Util.getDatastoreServiceInstance().put(repair);

        Entity lineRepair = new Entity("LineRepair", repair.getKey());
        lineRepair.setProperty("type", type);
        lineRepair.setProperty("description", description);
        lineRepair.setProperty("price", price);
        lineRepair.setProperty("qta", qta);
        lineRepair.setProperty("repairID",
                String.valueOf(repair.getKey().getId()));
        Util.getDatastoreServiceInstance().put(lineRepair);

        txn.commit();
    } finally {
        if (txn.isActive()) {
            txn.rollback();
        }
    }
}

Now i won't to search the repairs of the car given the plate and the date of the reparation. this is because I would like to add a condition that if there is already a repair on that date then add a LineRepair. I m using the class util of Code Lab Project. Here there are Entities Car and User. Thanks for any help

Edit: They key passed is the key of Car

Answer 1

You need to have a composite index with plate and date of repair and then a function to query your Repair entity for a given plate and date of repair values. If you get a response for the query , use getkey() for the query result and pass it to a function to create a corresponding linerepair entity.