Cloudant Sync - Android Datastore





Applications use Cloudant Sync to store, index and query local JSON data on a device and to synchronise data between many devices. Synchronisation is under the control of the application, rather than being controlled by the underlying system. Conflicts are also easy to manage and resolve, either on the local device or in the remote database.

Cloudant Sync is an Apache CouchDB™ replication-protocol-compatible datastore for devices that don't want or need to run a full CouchDB instance. It's built by Cloudant, building on the work of many others, and is available under the Apache 2.0 licence.

The API is quite different from CouchDB's; we retain the MVCC data model but not the HTTP-centric API.

This library is for Android and Java SE; an iOS version is also available.

If you have questions, please join our mailing list and drop us a line.

Using in your project

The library is published via Maven Central and using it in your project should be as simple as adding it as a dependency via maven or gradle.

There are currently four jar files for the datastore:

• cloudant-sync-datastore-core: the main datastore classes.
• cloudant-sync-datastore-android: Android specific classes.
• cloudant-sync-datastore-android-encryption: Android encryption specific classes.
• cloudant-sync-datastore-javase: Java SE specific classes.

Gradle or Maven

Add the maven repo and a compile time dependency on the appropriate datastore artifact. The datastore artifact dependency will include its other required dependencies and is different depending on the target use case as shown here:

1. Target is Android. If you also want datastore encryption see 2.
   • Gradle

   repositories {
       mavenLocal()
       mavenCentral()
   }
   
   dependencies {
       compile group: 'com.cloudant', name: 'cloudant-sync-datastore-android', version:'latest.release'
   }

   • Maven

   <project>
       <repositories>
       ...
       </repositories>
   
       <dependencies>
           <dependency>
               <groupId>com.cloudant</groupId>
               <artifactId>cloudant-sync-datastore-android</artifactId>
               <version>latest.release</version>
               <scope>compile</scope>
           </dependency>
       </dependencies>
   </project>

2. Target is Android and you want datastore encryption.
   • Gradle

   repositories {
       mavenLocal()
       mavenCentral()
   }
   
   dependencies {
       compile group: 'com.cloudant', name: 'cloudant-sync-datastore-android-encryption', version:'latest.release'
   }

   • Maven

   <project>
       <repositories>
       ...
       </repositories>
   
       <dependencies>
           <dependency>
               <groupId>com.cloudant</groupId>
               <artifactId>cloudant-sync-datastore-android-encryption</artifactId>
               <version>latest.release</version>
               <scope>compile</scope>
           </dependency>
       </dependencies>
   </project>

3. Target is Java SE.
   • Gradle

   repositories {
       mavenLocal()
       mavenCentral()
   }
   
   dependencies {
       compile group: 'com.cloudant', name: 'cloudant-sync-datastore-javase', version:'latest.release'
   }

   • Maven

   <project>
       <repositories>
       ...
       </repositories>
   
       <dependencies>
           <dependency>
               <groupId>com.cloudant</groupId>
               <artifactId>cloudant-sync-datastore-javase</artifactId>
               <version>latest.release</version>
               <scope>compile</scope>
           </dependency>
       </dependencies>
   </project>

You can see a fuller example in the sample application's build.gradle.

Note: Older versions than 0.3.0 had a separate Mazha jar. This was rolled into the main jar for distribution simplicity. The dependency needs removing from gradle and maven build files.

Tested Platforms

The library is regularly tested on the following platforms:

Android (via emulator):

• API Level 15
• API Level 16
• API Level 17
• API Level 18
• API Level 19
• API Level 21

Java:

• 1.8 (Java 8)

Example application

There is a sample Android application.

See the accompanying README.md for detailed instructions of how to run and build the sample.

Overview of the library

Once the libraries are added to a project, the basics of adding and reading a document are:

// Create a DatastoreManager using application internal storage path
File path = getApplicationContext().getDir("datastores", Context.MODE_PRIVATE);
DatastoreManager manager = new DatastoreManager(path.getAbsolutePath());

try {
    Datastore ds = manager.openDatastore("my_datastore");

    // Create a document
    DocumentRevision revision = new DocumentRevision();
    Map<String, Object> body = new HashMap<String, Object>();
    body.put("animal", "cat");
    revision.setBody(DocumentBodyFactory.create(body));
    DocumentRevision saved = ds.createDocumentFromRevision(revision);

    // Add an attachment -- binary data like a JPEG
    UnsavedFileAttachment att1 =
        new UnsavedFileAttachment(new File("/path/to/image.jpg"), "image/jpeg");
    saved.getAttachments().put(att1.name, att1);
    DocumentRevision updated = ds.updateDocumentFromRevision(saved);

    // Read a document
    DocumentRevision aRevision = ds.getDocument(updated.getId());
} catch (DatastoreException datastoreException) {

    // this will be thrown if we don't have permissions to write to the
    // datastore path
    System.err.println("Problem opening datastore: "+datastoreException);
} catch (DocumentException documentException) {

    // this will be thrown in case of errors performing CRUD operations on
    // documents
    System.err.println("Problem accessing datastore: "+documentException);
}

Read more in the CRUD document.

You can also subscribe for notifications of changes in the database, which is described in the events documentation.

The javadoc for the latest release version of the library is the definitive reference for the library. Each jar contains the full javadoc for itself and the other jars - this is for convenience at the slight expense of duplication.

Note that each class has an "API Status" declaration in the javadoc. This status is either "Public" or "Private". The general guidance is that API consumers (who are building software which uses this library) are discouraged from using "Private" API classes. This is because they may expose implementation details of the library which may be subject to change without notice or without change to the major version number. This behaviour follows the Semantic Versioning 2.0.0 specification.

Replicating Data Between Many Devices

Replication is used to synchronise data between the local datastore and a remote database, either a CouchDB instance or a Cloudant database. Many datastores can replicate with the same remote database, meaning that cross-device synchronisation is achieved by setting up replications from each device the the remote database.

Replication is simple to get started in the common cases:

URI uri = new URI("https://apikey:[email protected]/my_database");
Datastore ds = manager.openDatastore("my_datastore");

// Replicate from the local to remote database
Replicator replicator = ReplicatorBuilder.push().from(ds).to(uri).build();

// Fire-and-forget (there are easy ways to monitor the state too)
replicator.start();

Read more in the replication docs.

Finding data

Once you have thousands of documents in a database, it's important to have efficient ways of finding them. We've added an easy-to-use querying API. Once the appropriate indexes are set up, querying is as follows:

Map<String, Object> query = new HashMap<String, Object>();
query.put("name", "mike");
query.put("pet", "cat");
QueryResult result = indexManager.find(query);

for (DocumentRevision revision : result) {
    // do something
}

See Index and Querying Data.

For information about migrating your legacy indexing/query code to the new Cloudant Query - Android implementation.

See Index and Querying Migration

Conflicts

An obvious repercussion of being able to replicate documents about the place is that sometimes you might edit them in more than one place at the same time. When the databases containing these concurrent edits replicate, there needs to be some way to bring these divergent documents back together. Cloudant's MVCC data-model is used to do this.

A document is really a tree of the document and its history. This is neat because it allows us to store multiple versions of a document. In the main, there's a single, linear tree -- just a single branch -- running from the creation of the document to the current revision. It's possible, however, to create further branches in the tree. At this point your document is conflicted and needs some surgery to resolve the conflicts and bring it back to full health.

Learn more about this essential process in the conflicts documentation.

Known Issues

Some users on certain older versions of Android have reported the following exception:

java.lang.NoClassDefFoundError: javax/annotation/Nullable

To fix this issue, add the following dependency to your application's build.gradle:

compile 'com.google.code.findbugs:jsr305:3.0.0'

Contributors

See CONTRIBUTORS.

Contributing to the project

See CONTRIBUTING.

License

See LICENSE.