CRUD - Java SDK

Operaciones de escritura

You can create objects in a realm, update objects in a realm, and eventually delete objects from a realm. Because these operations modify the state of the realm, we call them writes.

Realm handles writes in terms of transactions. A transaction is a list of read and write operations that Realm treats as a single indivisible operation. In other words, a transaction is all or nothing: either all of the operations in the transaction succeed or none of the operations in the transaction take effect.

Un realm permite solo una transacción de escritura abierta a la vez. Realm bloquea otros guardados en otros hilos hasta que la transacción abierta haya finalizado. Por consecuencia, no hay condiciones de competencia al leer valores del realm dentro de una transacción.

Cuando finalices tu transacción, Realm la confirma o la cancela:

• When Realm commits a transaction, Realm writes all changes to disk. For synced realms, Realm queues the change for synchronization with Atlas App Services.

• Cuando Realm cancela una transacción de escritura o una operación en la transacción provoca un error, todos los cambios se descartan (o se "revierten").

SyncConfiguration config = new SyncConfiguration.Builder(app.currentUser(), PARTITION)
        .allowQueriesOnUiThread(true)
        .allowWritesOnUiThread(true)
        .build();
Realm.getInstanceAsync(config, new Realm.Callback() {
    @Override
    public void onSuccess(Realm realm) {
        Log.v(
                "EXAMPLE",
                "Successfully opened a realm with reads and writes allowed on the UI thread."
        );
    }
});

val config = SyncConfiguration.Builder(app.currentUser(), PARTITION)
    .allowQueriesOnUiThread(true)
    .allowWritesOnUiThread(true)
    .build()
Realm.getInstanceAsync(config, object : Realm.Callback() {
    override fun onSuccess(realm: Realm) {
        Log.v("EXAMPLE", "Successfully opened a realm with reads and writes allowed on the UI thread.")
    }
})

Managed Objects

Managed objects are live Realm objects that update based on changes to underlying data in Realm. Managed objects can only come from an open realm, and receive updates as long as that realm remains open. Managed objects cannot be passed between threads.

Objetos no administrados

Los objetos no administrados son instancias de objetos de Realm que no están activos. Puede obtener un objeto no administrado construyendo manualmente un objeto de Realm o llamando a Realm.copyFromRealm(). Se pueden transferir objetos no administrados entre subprocesos.

Ejecutar una Transacción

Realm represents each transaction as a callback function that contains zero or more read and write operations. To run a transaction, define a transaction callback and pass it to the realm's write method. Within this callback, you are free to create, read, update, and delete on the realm. If the code in the callback throws an exception when Realm runs it, Realm cancels the transaction. Otherwise, Realm commits the transaction immediately after the callback.

realm.executeTransaction(r -> {
    // Create a turtle enthusiast named Ali.
    TurtleEnthusiast ali = r.createObject(TurtleEnthusiast.class, new ObjectId());
    ali.setName("Ali");
    // Find turtles younger than 2 years old
    RealmResults<Turtle> hatchlings = r.where(Turtle.class).lessThan("age", 2).findAll();
    // Give all hatchlings to Ali.
    hatchlings.setObject("owner", ali);
});

realm.executeTransaction { r: Realm ->
    // Create a turtle enthusiast named Ali.
    val ali = r.createObject(TurtleEnthusiast::class.java, ObjectId())
    ali.name = "Ali"
    // Find turtles younger than 2 years old
    val hatchlings =
        r.where(Turtle::class.java).lessThan("age", 2).findAll()
    // Give all hatchlings to Ali.
    hatchlings.setObject("owner", ali)
}