Whenever, we create a document in PouchDB, a new field _rev is generated, and it is known as revision marker. The _rev‘s value is a unique random number, each time we make changes to the document the value of _rev is changed.

You can update an existing document in PouchDB using the (_rev). To do so, first of all retrieve the _rev value of the document we want to update. Now, place the contents that are to be updated along with the retrieved _rev value in a new document, and finally insert this document in PouchDB using the put() method.

Example

Assume we have a document in PouchDB with id 001 which has details of a person. In order to update this document, we should have its rev number. Therefore, to retrieve the contents of the document the following code is used.

//Requiring the package
var PouchDB = require(''PouchDB'');

//Creating the database object
var db = new PouchDB(''my_database'');

//Reading the contents of a Document
db.get(''001'', function(err, doc) {
   if (err) {
      return console.log(err);
   } else {
      console.log(doc);
   }
});

On executing the above code, you will receive the following output.

{
   _id: ''001'',
   _rev: ''3-552920d1ca372986fad7b996ce365f5d'',
   name: ''Raju'',
   age: 23,
   designation: ''Designer'' 
}

Now, using the _rev you can update the value of the key “age” to 26, as shown in the following code.

//Requiring the package
var PouchDB = require(''PouchDB'');

//Creating the database object
var db = new PouchDB(''my_database'');

//Preparing the document for update
doc = {
   age: 26,
   _rev: ''3-552920d1ca372986fad7b996ce365f5d'',
   }

//Inserting Document
db.put(doc);

//Reading the contents of a Document
db.get(''001'', function(err, doc) {
   if (err) {
      return console.log(err);
   } else {
      console.log(doc);
   }
});

Save the above code in a file with the name Update_Document.js. Open the command prompt and execute the JavaScript file using node as shown below.

C:Pouch_Examples>node Update_Document.js

This updates the contents of the given document that exists in the database named my_database which is stored locally. The following message is displayed on the console.

{ 
   name: ''Raju'',
   age: 26,
   designation: ''Designer'',
   _id: ''001'',
   _rev: ''2-61b523ccdc4e41a8435bdffbb057a7a5'' 
}

Updating a Document in a Remote Database

You can also update an existing document in a database that is stored remotely on the server (CouchDB).

To do so, instead of a database name you need to pass the path to the database in CouchDB, which contains the document that is to be updated.

Example

Suppose there is a database named my_database in the CouchDB server. Then, if you verify the list of databases in CouchDB using the URL http://127.0.0.1:5984/_utils/index.html you will get the following screenshot.

By clicking on the database named my_database, you can see the following screenshot. Here, you can observe that this database contains a document with id 001.

Following is an example of updating the age of the document having id as “001” that exists in a database named my_database which is stored in the CouchDB server.

//Requiring the package
var PouchDB = require(''PouchDB'');

//Creating the database object
var db = new PouchDB(''http://localhost:5984/my_database'');

//Preparing the document for update
doc = {
   age: 26,
   _rev: ''3-552920d1ca372986fad7b996ce365f5d'',
   }

//Inserting Document
db.put(doc);

//Reading the contents of a Document
db.get(''001'', function(err, doc) {
   if (err) {
      return console.log(err);
   } else {
      console.log(doc);
   }
});   

Save the above code in a file with the name Remote_Update_Document.js. Open the command prompt and execute the JavaScript file using node as shown below.

C:PouchDB_Examples >node Remote_Update_Document.js

This updates the contents of the given document that exists in the database named my_database which is stored in CouchDB. The following message is displayed on the console.

{
   _id: ''001'',
   _rev: ''2-b9640bffbce582c94308905eed8bb545'',
   name: ''Raju'',
   age: 26,
   designation: ''Designer'' 
}