PouchDB Replication

Replication is a very important feature of PouchDB. It facilitates you to make a copy of a database. You can replicate either a PouchDB instance stored locally or a CouchDB instance stored remotely.

While using this method, you can directly pass the location of source and destination databases in String format, or you can pass objects representing them.

Syntax

Both the source and targets can be either PouchDB instances or CouchDB instances.

Replicating PouchDB (Local) to CouchDB

Let's take a database named "sample_database" in PouchDB which have 3 documents doc1, doc2, and doc3, having following content.

{ id: '001',
    key: '001',
    value: { rev: '1-20a74c908d2c4e168d47571c4c6b4d5f' },
    doc:
     { name: 'Ajeet',
       age: 21,
       Designation: 'Programmer',
       _id: '001',
       _rev: '1-20a74c908d2c4e168d47571c4c6b4d5f' } },
  { id: '002',
    key: '002',
    value: { rev: '1-89b7169dca7c47558e0aa47474b3e873' },
    doc:
     { name: 'Robert',
       age: 34,
       Designation: 'Designer',
       _id: '002',
       _rev: '1-89b7169dca7c47558e0aa47474b3e873' } },
  { id: '003',
    key: '003',
    value: { rev: '1-5cf7e1bbd3bf4765a72a17e164692def' },
    doc:
     { name: 'Rohila',
       age: 15,
       Designation: 'Student',
       _id: '003',
       _rev: '1-5cf7e1bbd3bf4765a72a17e164692def' } } ]

Now create a replication of this database in CouchDB:

//Requiring the package 
var PouchDB = require('PouchDB');
var localDB = 'sample_database';
//Creating remote database object 
var remoteDB = 'http://localhost:5984/sample_database';
//Replicating a local database to Remote 
PouchDB.replicate(localDB, remoteDB); 
console.log ("Database replicated successfully");

Save the above code in a file named "Remote_Replication.js" within a folder name "PouchDB_Examples". Open the command prompt and execute the JavaScript file using node:

Output

Verification

You can open CouchDB link and see that a database "sample_database" is created.

Image: Replication3

You can also see all three documents here:

Replicate CouchDB to PouchDB

Let's create a database named "remotedb" on CouchDB server with three documents doc1, doc2, and doc3, having contents as following:

doc1 = {_id: '001', name: 'Jen', age: 20, Designation: 'Teacher'}
doc2 = {_id: '002', name: 'Jacob', age: 24, Designation: 'Lawyer'}
doc3 = {_id: '003', name: 'Johnny', age: 36, Designation: 'Plumber'}

Let's replicate this database in local server PouchDB.

//Requiring the package
var PouchDB = require('PouchDB');
var localdb = 'remotedb';
var remotedb2 = 'http://localhost:5984/remotedb';
//Replicating a local database to Remote
PouchDB.replicate(remotedb2, localdb);
console.log("Database replicated successfully to PouchDB");

Save the above code in a file named "Local_Replication.js" within a folder name "PouchDB_Examples". Open the command prompt and execute the JavaScript file using node:

Output:

You can verify if the database is replicated in your Pouch instance by using the following code.

//Requiring the package
var PouchDB = require('PouchDB');
//Creating the database object
var db = new PouchDB('remotedb');
//Retrieving all the documents in PouchDB
db.allDocs({include_docs: true, attachments: true}, function(err, docs) {
   if (err) {
      return console.log(err);
   } else {
      console.log(docs.rows);
   }
});

Save the above code in a file named "Verify_Replication.js" within a folder name "PouchDB_Examples". Open the command prompt and execute the JavaScript file using node:

Output

{ id: '001',
    key: '001',
    value: { rev: '1-a323b7088ac944b382e15c33cb771b6d' },
    doc:
     { name: 'Jen',
       age: '20',
       Designation: 'Teacher',
       _id: '001',
       _rev: '1-a323b7088ac944b382e15c33cb771b6d' } },
  { id: '002',
    key: '002',
    value: { rev: '1-20f14cf10f3ffacd1b5447737240c995' },
    doc:
     { name: 'Jacob',
       age: '24',
       Designation: 'Lawyer',
       _id: '002',
       _rev: '1-20f14cf10f3ffacd1b5447737240c995' } },
  { id: '003',
    key: '003',
    value: { rev: '1-6668a7d03dff7b43f37528f24061001b' },
    doc:
     { name: 'Johnny',
       age: '36',
       Designation: 'Plumber',
       _id: '003',
       _rev: '1-6668a7d03dff7b43f37528f24061001b' } } ]

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