Monarchy

A wrapper over Realm, that exposes RealmResults as various forms of LiveData.

With that, you can use a singleton Monarchy instance to manage Realm queries, and possibly make it easier to hide Realm as implementation of the data layer.

Adding to project

To use Monarchy, you need to add as a dependency:

implementation 'com.github.Zhuinden:realm-monarchy:0.5.1'

And it's available on Jitpack, so you need to add

allprojects {
    repositories {
        // ...
        maven { url "https://jitpack.io" }
    }
    // ...
}

How can I use it?

Initialization

Initialize Monarchy, and create a new Monarchy instance (for a given RealmConfiguration):

Monarchy.init(this); // need to call this only once
monarchy = new Monarchy.Builder()
    .setRealmConfiguration(new RealmConfiguration.Builder()
         .deleteRealmIfMigrationNeeded()
         .initialData(realm -> {
              RealmDog dog = realm.createObject(RealmDog.class);
              dog.setName("Corgi");
         }).build()
    ).build();

Queries

Create queries as LiveData, and observe them

LiveData<List<RealmDog>> dogs = monarchy.findAllCopiedWithChanges(realm -> realm.where(RealmDog.class));
dogs.observe(this, dogs -> {...});

You can also create a Mapper which will map the RealmObject to something else

LiveData<List<Dog>> dogs = monarchy.findAllMappedWithChanges(realm -> realm.where(RealmDog.class), dog -> Dog.create(dog.getName()));
dogs.observe(this, dogs -> {...});

Using the Android Architecture Components: Paging Library, you can now also obtain the RealmResults as a LiveData<PagedList<T>>.

DataSource.Factory<Integer, RealmDog> realmDataSourceFactory = monarchy.createDataSourceFactory(realm -> realm.where(RealmDog.class));
DataSource.Factory<Integer, Dog> dataSourceFactory = realmDataSourceFactory.map(input -> Dog.create(input.getName()));
LiveData<PagedList<Dog>> dogs = monarchy.findAllPagedWithChanges(realmDataSourceFactory,
                                                new LivePagedListBuilder<>(dataSourceFactory, 20));
dogs.observe(this, dogs -> {...});

You can also synchronously get mapped/copied results, but it's generally not recommended; it is preferred to find results with changes instead.

Writes

You can do either synchronous transaction, or have the transaction be executed asynchronously on a dedicated single-threaded pool.

For synchronous transaction, you can use runTransactionSync(Realm.Transaction).

monarchy.runTransactionSync(realm -> {
    RealmDog dog = realm.createObject(RealmDog.class);
    dog.setName("Doge");
});

For asynchronous transaction, you can use writeAsync(Realm.Transaction).

monarchy.writeAsync(realm -> {
    RealmDog dog = realm.createObject(RealmDog.class);
    dog.setName("Doge");
});

Working with Realm instances

Instead of using Realm.getDefaultInstance() and close(), now you should just do

monarchy.doWithRealm((realm) -> {
    ....
});

And otherwise expose the queries as LiveData, and observe them. Whether a LiveData has observers or not will properly manage the Realm lifecycle.

Information

Listening for copied/mapped results happens on the background looper thread.

Listening for paged results happens on the background looper thread.

Listening for managed results happens on the UI thread.

Possible FAQs

Why isn't this written with Rx operators?

Because managing ref counting and doing specific callbacks when ref-counting is tricky, while LiveData makes it trivial.

Observable.just(5)
          .replay(1)
          .autoConnect(0)
          .doOnSubscribe(/* onActive */)
          .doOnUnsubscribe(/* onInactive */)
          .subscribe()

or something like that. Tricky stuff. So if you need LiveData exposed to Rx, then just use:

Flowable<List<Dog>> dogs = Flowable.fromPublisher(LiveDataReactiveStreams.toPublisher(lifecycleOwner, liveData));

with the help of

implementation "android.arch.lifecycle:reactivestreams:1.1.1"

How do I open a Realm instance and close it manually, without being in a block?

This is where most errors in Realm usage come from, so I specifically did not add an open()/close() method to Monarchy.

Realm already manages a reference counted cache for thread-local Realm instances, where of course getInstance() increases ref count. So if that doesn't suit you, feel free to keep your own ThreadLocal<Realm> cache.

When should I compact the Realm?

Probably when you've finished every Activity. When's that? If you have only 1 finishing Activity, then it's easy, if you have more Activities, then that's a different problem :D

How should I do schema migrations?

RealmAutoMigration can help.

Once you're done migrating your current fields to new fields, it can match the fields and migrate from one schema to another, removing any mismatched properties (or adding the new ones).

Why is this library possible?

Because LiveData from the Android Architecture Components is the best thing since sliced bread.

License

Copyright 2017 Gabor Varadi

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

cuihujun/realm-monarchy