#30 Creating with Transaction

[Nathaniel Sherry]

Suppose I have Person who owns Cars:

<composed selector='Person'>
    <mapped selector='cars'>
        <ref selector='car' m:href='Car'/>
    </mapped>
</composed>

Lets say I want to add a new car to this person's collection:

Transaction<Person> txPerson = repo.connect(this);
Person p = txPerson.retrieve("Person", "1");

Transaction<Car> txCar = repo.connect(this);
Car c = txCar.create("Car");

p.getCars().put("carname", c);
txPerson.post();

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Will posting just the Person Transaction be enough to ensure that the new car is posted to the database, or should txCar.post be called after creating it?

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Can a new Car be created using the txPerson transaction like so:

Car s = (Car) txPerson.create("Car");

Will this work, is it considered poor form, will there be any unintended side-effects?

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Should txCar be closed after creating the Car, or should it be left open until the changes to Person are posted?

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If the changes to Person are posted, and then the Car is modified and posted using txCar, will everything update as expected?

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If I execute the following code:

Transaction<Person> txPerson1 = repo.connect(this);
Person p1 = txPerson1.retrieve("Person", "1");

Transaction<Car> txCar = repo.connect(this);
Car c1 = txCar.create("Car");
Car c2 = txCar.create("Car");

p1.getCars().put("carname", c1);

Transaction<Person> txPerson2 = repo.connect(this);
Person p2 = txPerson2.retrieve("Person", "1");

p2.getCars().put("carname", c2);

txPerson2.post();

will txPerson2 retrieve an in-memory, modified instance of person-1, or a fresh copy from the database? When I post txPerson2, will it add c1 to the list of cars, or just c2?