This example is a simple Android application in which the user can save a review with a rating and name property to a Couchbase Lite database. It uses the TabLayout and ViewPager components to illustrate 3 different scenarios, each one being in a separate tab.
Unique (1st tab): The _id field is randomly generated by Couchbase Lite. A new document is persisted to the database every time the Save button is pressed. The document stored will have the following properties:
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{
“_id”: “008c30d0-0f57-4477-8fa5-b9685f410f9e”,
“_rev”: “1-38fd691714c1ed19ce48a1f4a87c20d9”,
“name”: “chef123”,
“rating”: 4,
“type”: “unique”
}
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Conflict (2nd tab): The _id field is set to whatever the user entered in the text input. Pressing Save will persist a new document to the database or update it if one already exists with this ID.
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{
“_id”: “chef123”,
“_rev”: “1-38fd691714c1ed19ce48a1f4a87c20d9”,
“rating”: 4,
“type”: “conflict”
}
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P2P (3rd tab): The text input field takes the URL of a target Couchbase Lite or Sync Gateway database of the form http://{ip}:55000/ratingapp.
Below the ViewPager, there is a Switch toggle button to start/stop the continuous pull/push replications to a remote database. This would usually be the URL of the Sync Gateway running on the cloud. You can change the remote URL in StorageManager.java to your own Sync Gateway instance (see section below to deploy Couchbase Server and Sync Gateway).
Finally, there is a table on the bottom half of the screen that displays the following:
On the 1st tab, it shows the number of reviews for each possible value. It’s using a query with a group level set to 1 to aggregate the documents with the same rating and a reduce function to count them.
The code to register the view is in StorageManager.java:
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View ratingsView = database.getView(UNIQUE_RATINGS_VIEW);
ratingsView.setMapReduce(new Mapper() {
@Override
public void map(Map<String, Object> document, Emitter emitter) {
if (document.get(“type”).equals(“unique”)) {
emitter.emit(document.get(“rating”).toString(), null);
}
}
}, new Reducer() {
@Override
public Object reduce(List<object width=“300” height=“150”> keys, List<object> values, boolean rereduce) {
return new Integer(values.size());
}
}, “16”);
And a live query is instantiated in <strong>MainActivity.java</strong> to notify the Recycler View adapter when the view index has changed:
<pre>
LiveQuery liveQuery = storageManager.database.getView(StorageManager.UNIQUE_RATINGS_VIEW).createQuery().toLiveQuery();
liveQuery.setGroupLevel(1);
liveQuery.setDescending(true);
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On the 2nd and 3rd tab, it displays the number of conflicting revisions of a document. It only shows the number of conflicting revisions but it would also be possible to resolve the conflicts by using the database.getDocument({id}).getConflictingRevisions() method.
Deploying Sync Gateway and Couchbase Server
Deploy a fresh Sync Gateway and Couchbase Server instance for this application with Tutum. Log on or create a new account on Tutum.co, then link it to your PaaS account (Digital Ocean, AWS…). On the Nodes tab, create a new node and choose the PaaS of your choice. In the tag field, add rating-app.Next, select the Stacks tab with this Tutum file and click create. This stack includes a Sync Gateway container linked with a Couchbase Server container.NOTE: The Sync Gateway container will fail to run because it’s trying to connect to a Couchbase Server bucket that doesn’t exist. It may take several minutes for Couchbase Server to be deployed and for the admin console to be reachable on http://{ip}:8091. Once it’s reachable, create an account and a bucket called default (the Sync Gateway configuration file expects the bucket to be named default). Once the bucket is created, head back to the Tutum Services tab and restart the Sync Gateway container (or just click the Run button as it should be stopped).
Removing all documents from a database
Use the delete-documents/delete.js script to remove all documents in a particular database. It could be a Couchbase Lite or Sync Gateway database. Replace the hostname in the script with the one of the target database you wish to delete the documents from.
