RxPaper

RxPaper is an RxJava wrapper for the cool Paper library. It's a clean rewrite of the original RxPaper library by César Ferreira.

For the RxJava 2 version please go to RxPaper2.

Rationale

Sometimes you need storage for arbitrary objects on disk, but do not want to store them in a relational database with all the associated problems: writing ORMs, composing the queries, updating scripts. For this purpose NoSQL data storages were created: schemaless document repositories where to store arbitrary data that's not structured.

RxPaper allows access to Paper, which is a NoSQL data storage for Android that allows you to save arbitrary objects in system files called Books. Serialization and deserialization is done using efficient Kryo.

The Paper/Kryo combination supports some partial data structure changes. Check Paper's README for more information.

Updating from 1.X

As PaperDb 2.0 has updated from Kryo 3 to Kryo 4, the internal representation model has changed. PaperDb deals with these changes internally, so the migration should be transparent. If you find any data compatibility bug, please create a ticket.

Usage

Object model handling

RxPaper is subject to the same restrictions as the current version of Paper when the library was last updated. As of Paper 1.5, the library can work with empty constructors and all-arg constructors. Some other combinations would need to be tested by the library user.

I personally recommend using immutable objects, as it makes data handling way simpler on both sides. An immutable object has an all-args constructor, doesn't allow any null fields, and keeps all fields public and final. Like any other dto in Java, it is recommended to implement your own version of equals, hashCode and toString.

As of Paper 1.5 you can also add your own serializers by calling Paper.addSerializer(). Partial structure changes are supported too, as described on Paper's README.

Threading

All operations are run on the Scheduler provided on the constructor, or Schedulers.io() by default. When subscribing to them, specially if using the data to be applied to UI; it's recommended to use the operator observeOn(Scheduler) to see the changes on any desired thread, i.e. Android's main thread.

Initialization

Before the library is usable it requires initializing the underlying Paper library. You only have to initialize RxPaper by calling:

RxPaperBook.init(context);

Working on a book

RxPaper works on books, and each is a folder on the system. A book is only opened and closed on an operation, but you can check the Paper repository for specifics. To make sure no operations are done on the main thread, any operations done on a book can be executed on one Scheduler provided in the constructor. To create an instance of RxPaper the library provides several flavours.

RxPaperBook.with();

Works with the default book, and executes operations on Schedulers.io().

RxPaperBook.with(Schedulers.newThread());

Works with the default book, and executes operations on any provided scheduler.

RxPaperBook.with("my_book_name");

Works with a custom book with the provided id/name, and executes operations on Schedulers.io().

RxPaperBook.with("my_book_name", Schedulers.newThread());

Works with a custom book with the provided id/name, and executes operations on any provided scheduler.

Writing a value

Write is a Completable operation, a subset of Observable<T> without a return value, just success/error. Completables can be converted back to Observables by using the operator toObservable().

RxPaperBook book = RxPaperBook.with("my-book");
Completable write = book.write(key, value);
// Because RxJava is lazily evaluated, the operation is not executed until the Observable is subscribed.
write.subscribe(new Completable.CompletableSubscriber() {
            @Override
            public void onCompleted() {
                // Operation suceeded
            }

            @Override
            public void onError(Throwable e) {
                // Operation failed
            }

            @Override
            public void onSubscribe(Subscription d) {
                // Called once on creation
            }
        });

Every key written is stored as a file on the system under the folder specified by the book.

Reading a value

Reading is a Single<T> operation, a subset of Observable<T> that returns just a single element and then completes. Singles can be converted back to Observables by using the operator toObservable(). Reading comes in two flavours:

Single<ComplexObject> read = book.read(key);
read.subscribe(new SingleSubscriber<ComplexObject>() {
            @Override
            public void onSuccess(ComplexObject value) {
                // Operation succeeded and returned a value
            }

            @Override
            public void onError(Throwable error) {
                // Operation failed
            }
        });

ComplexObject defaultValue = new ComplexObject();
Single<ComplexObject> readOrDefault = book.read(key, defaultValue);
readOrDefault.subscribe(new SingleSubscriber<ComplexObject>() {
            @Override
            public void onSuccess(ComplexObject value) {
                // Operation succeeded and returned a value
            }

            @Override
            public void onError(Throwable error) {
                // Operation failed
            }
        });

read(key) fails with IllegalArgumentException if the key is not found. read(key, defaultValue) returns a defualt value if the key is not found.

If the subscriber is not of the same type as the value stored expect a ClassCastException.

Make sure to read the rules on how object models are handled on the section above.

Observing changes on a key

All write operations are naively forwarded into a PublishSubject<?> by default, which makes it possible to observe all changes for a specific key. Observing is an Observable<T> operation that never completes.

Observable<ComplexObject> observe = book.observe(key, ComplexObject.class);
observe.subscribe(new Subscriber() { /* ... */ });

Observe filters on both the key and the type. Another version of observe that filters only on key and casts any values unsafely is provided under the name observeUnsafe(). It's recommended to use it with strict care.

Exists

Exists is a Single<Boolean> operation that returns true if the key is on the current book, or false otherwise.

Single<Boolean> exists = book.exists(key);
exists.subscribe(new SingleSubscriber<Boolean>() { /* ... */ });

Delete

Delete is a Completable operation. Deletes data stored for a key on the current book. It will still succeed even if the key is not found.

Completable delete = book.delete(key);
delete.subscribe(new Completable.CompletableSubscriber() { /* ... */ });

Keys

Keys is a Single<List<String>> operation that returns a list of all keys stored on the current book.

Single<List<String>> keys = book.keys();
exists.subscribe(new SingleSubscriber<List<String>>() { /* ... */ });

Destroy

Destroy is a Completable operation that deletes all keys and values on the current book.

Completable destroy = book.destroy();
destroy.subscribe(new Completable.CompletableSubscriber() { /* ... */ });

Distribution

Add as a dependency to your build.gradle

    repositories {
        ...
        maven { url "https://jitpack.io" }
        ...
    }
    
    dependencies {
        ...
        compile 'com.github.pakoito:RxPaper:2.1.0'
        ...
    }

or to your pom.xml

    <repositories>
        <repository>
            <id>jitpack.io</id>
            <url>https://jitpack.io</url>
        </repository>
    </repositories>
    
    <dependency>
        <groupId>com.github.pakoito</groupId>
        <artifactId>RxPaper</artifactId>
        <version>2.1.0</version>
    </dependency>

License

The MIT License (MIT)

See LICENSE.md

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