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Showing posts with label MongoDB. Show all posts

Friday, 7 July 2017

Mongoose iterate records over results using async module

Mongoose iterate records over results using callback functions

Download the async module in nodeJs Project?

npm install async --save

Inculude the module in NodeJS?

async= require('async');

Following are code snippet example which demostrate, how to update the listing?

app.get("get_chat_messages", function(req, res) {
    var vid = req.query.vid;
    
    //Get the records from mongoose
    AjaxChatMessage.find({vid: vid}, function(err, items) {

    //initalize vars
    var index
    var results={}

    //include the module
    async= require('async');

    //iterate records
   async.each(items,     
     function(item, callback){  
         index=items.indexOf(item);
         results[index]={};
         results[index].text=item.text;
         results[index].vid=item.vid;
         results[index].user_display_name=item.user_display_name;
         results[index].id=item.id;
         results[index].photo=item.user.photo;
         results[index].logintype=item.user.logintype;
         
       if((items.indexOf(item)+1)==items.length){
           res.send(results);
       }
     });
     
    }).sort({id: 1}).populate('user');
}

Monday, 5 June 2017

Mongoose Tutorial - listing records, Add Record, update record and delete record

Question: How to install the mongoose?

npm install mongoose

Question: How to update the mongoose?

npm update mongoose

Question: How to Start the mongoose?
Include the mongoose in the project

var mongoose = require('mongoose');

Make the Db connection with mongodb

mongoose.connect('mongodb://localhost:27017/test');
var db = mongoose.connection;

Check the Error OR Success on Db Connection

db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
   console.log("MongoDB connected Successfully.!");
});

Question: How to Create Model with mongoose?
Here we have set the two fields only, you can add more if required.

var TodoSchema = mongoose.Schema({
  id: String, //datatype is string
  name: String, //datatype is string          
});       
var Todo = mongoose.model('Todo', TodoSchema);

In mongoose.model, the first argument is the singular name of the collection.
Mongoose automatically looks for the plural version with lowercase of your model name.
means for Todo, it will look todos.

Question: How to set unique key for a field?

var TodoSchema = mongoose.Schema({
  id: { type: Number, unique: true}, 
  name: String, //datatype is string          
});

Question: How to set unique key and required for a field?

var TodoSchema = mongoose.Schema({
  id: { type: Number, unique: true }, 
  email: { type: String, unique: true, required:true }, 
  name: String, //datatype is string          
});

Question: How to list the records from mongodb?

var cursor = Todo.find({ }).cursor();
cursor.on('data', function(doc) {
    jsonData[doc.id] = doc.name;  
});
cursor.on('close', function() {
    console.log(jsonData);                   
});

Question: How to save the record?

var TodoDetails = new Todo({ id: "10",name:"this id test message"});
TodoDetails.save(function (err) {if (err) console.log ('Error on save!')});

Question: How to update the record?

 Todo.update({id: "10" }, { $set: { name: "this is update message" }}, {}, function(){
             console.log("Update the records successfully");
        })

Question: How to delete the record?

    Todo.find({ id:"10" }).remove( function(){
     console.log("Record deleted successfully");
    });

Question: How to delete the document and check is it deleted?

Todo.find({ id:"10" }).remove( function(err, effectedRows){
    if(err){
         console.log("Unable to delete the record");
    }
    if(effectedRows.n==0){
        console.log("Zero Record deleted");
    }else{
        console.log("Record deleted successfully");
    }
     
 });

Question: What are the difference between mongoose.model and mongoose.Schema?
Model is an object that gives you easy access to a collection, allowing you to query the collection and use the Schema to validate any documents you save to that collection. It is created by combining a Schema, a Connection, and a collection name.

Schema is an object that defines the structure of the documents that will be stored.
it enables you to define types and validators for all data.

Question: How to get first record(s) from listing?

Todo.findOne({ 'name': 'kumar' }, 'id', function (err, person) {
  if (err) return handleError(err);
    console.log(person);          

})

Question: How to fetch specific column?

  Todo.find({ 'name': 'kumar' }, 'id name', function (err, person) {
          if (err) return handleError(err);
            //console.log(person);          
             res.send(person);
        })

Question: How to limit the number of records?
You can use limit method.

Todo.find({}, 'id name', function (err, person) {
  if (err) return handleError(err);
    console.log(person);          
     
}).limit(3);

Question: How to get listing by name in ascending order?
You can use sort method, -1 means descending order, 1 means ascending order.

Todo.find({}, 'id name', function (err, person) {
  if (err) return handleError(err);
    console.log(person);          
     
}).limit(3).sort({ name: -1 });

Question: How to use "in" in where clause?

Todo.find({ name: { $in: ['arun', 'gupta']}, 'id name', function (err, person) {
  if (err) return handleError(err);
    console.log(person);          
     
}).limit(3).sort({ name: -1 });

Question: Give full Query example?

Todo.find({ 
    occupation: /host/,
    'name.last': 'Ghost',
    age: { $gt: 17, $lt: 66 },
    name: { $in: ['technology', 'web'] }

}, 'id name', function (err, person) {
  if (err) return handleError(err);
    //Here will be display all the records
    console.log(person);               
}).limit(3).sort({ name: -1 });

Question: How to create custom function in mongoose.model?
In schema/Model file (Create a custom function)

var TodoSchema = mongoose.Schema({
  id: { type: Number, unique: true}, 
  name: String, //datatype is string          
});
TodoSchema.statics.findByIdTest = function (todoId,cb) {
  return this.model('Todo').find({ id: todoId }, cb);
};

How to use controller file.

Todo.findByIdTest(2677,function(error, data){
    console.log(data);    
});

Tuesday, 30 May 2017

What is mongoose? How to use mongoose with nodejs for mongodb?

How to use mongoose with nodejs for mongodb?

Question: What is mongoose in node js?
mongoose is an object modeling package for Node that essentially works like an ORM.

Question: How to install mongoose in node js?

npm install mongoose

Question: What is the --save option for npm install?
When we do "npm install", then it install the modules.
If we need to update the version of module in package.json, then we have to do it manually.
BUT when we do "npm install --save", then it install the modules and update the package.json automatically.

Question: What is difference between dependencies and devDependencies?
dependencies are modules your project depends on, devDependencies are modules you use to develop your project.

Examples of dependencies are request, through2 and concat-stream.
Examples of devDependencies are grunt, mocha, eslint, tape, and browserify.

Question: How to connect to MongoDB database?

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost:27017/mongodb');
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
   console.log("MongoDB connected Successfully.!");
});

Question: How to define the Schema in mongoose?

var userSchema = mongoose.Schema({
  name: String, //datatype is string
  username: { type: String, required: true, unique: true }, //type is string and its required field and its unique
  password: { type: String, required: true },
  admin: Boolean,
  location: String,  
  created_at: Date //datatype of date  
});

Question: How to compile the Schema with model?

var User = mongoose.model('User', userSchema);
module.exports = User;

Here User inside "mongoose.model" is a User model, where all the data will be managed.
var User is an Model Object which will be used to process on the document.

Question: What are different type of data types in mongodb?
String
Number
Date
Buffer
Boolean
Mixed
ObjectId
Array

Question: How to add a record in document with model?

var userDetails = new User({ name: 'Test user',username:'testuser',password:'test12@',location:'mohali' });
userDetails.save(function (err) {if (err) console.log ('Error on save!')});
console.log(userDetails);

Question: How to add a record in document with model with FULL CODE?

//include the js
var mongoose = require('mongoose');

//database connection
mongoose.connect('mongodb://localhost:27017/mongodb');

//Create schema
var userSchema = mongoose.Schema({
  name: String, //datatype is string
  username: { type: String, required: true, unique: true }, //type is string and its required field and its unique
  password: { type: String, required: true },
  admin: Boolean,
  location: String,  
  created_at: Date //datatype of date  
});

//create User Object
var User = mongoose.model('User', userSchema);

//Save User details in database
var userDetails = new User({ name: 'Test user',username:'testuser',password:'test12@',location:'mohali' });
userDetails.save(function (err) {if (err) console.log ('Error on save!')});
console.log(userDetails);

Question: How to fetch all records?

User.find({}, function(err, users) {
  if (err) {throw err;}
  console.log(users);
});

Question: How to fetch one record?

User.find({ username: 'testuser' }, function(err, user) {
  if (err) throw err;

  // object of the user
  console.log(user);
});

Question: How to update record?

        User.update({username: 'testuser' }, { $set: { name: "New name" }}, {}, function(){
            //here comes after update the record
        })

Question: How to delete record?

  User.find({ username: 'testuser'  }).remove( function(){
  //write here your code after delete
 });

Wednesday, 22 March 2017

Express js Interview questions and answers

Question: How to install express js in node?
use following command to install express js.

npm install express

Question: How to use express js in node?
use require to include express module.

var app = require('express')();

Question: How to use handle get request in express Js?

/*Include require module*/
var app = require('express')();
var http = require('http').Server(app);

app.get('/', function (req, res) {
   console.log("Got a GET request for the homepage"); //Shown in console
   res.send('This is GET Method for Homepage'); //Display as response
})

/*Start listing 8080 port*/
http.listen('8080', function() {
    console.log('listening on *:8080');
});

Question: How to use handle post request in express Js?

/*Include require module*/
var app = require('express')();
var http = require('http').Server(app);

app.post('/user_list', function (req, res) {
   console.log("Got a POST request for the user_list URL"); //Shown in console
   res.send('This is POST Method for user_list URL');//Display as response
})

/*Start listing 8080 port*/
http.listen('8080', function() {
    console.log('listening on *:8080');
});

Question: How to use handle GET/POST request for same URL expressJs?

/*Include require module*/
var app = require('express')();
var http = require('http').Server(app);

//This is POST Request
app.post('/add_user', function (req, res) {
   console.log("Got a POST request for the add_user URL"); //Shown in console
   res.send('This is POST Method for add_user URL');//Display as response
})

//This is Get Request
app.get('/user_list', function (req, res) {
   console.log("Got a GET request for the user_list URL"); //Shown in console
   res.send('This is GET Method for user_list URL');//Display as response
})

/*Start listing 8080 port*/
http.listen('8080', function() {
    console.log('listening on *:8080');
});

Question: How to use handle GET request for all URL start with ab* ?

app.get('/ab*', function(req, res) {   
   console.log("Got a GET request for /ab*");
   res.send('Page Regex Match');
})

Question: How to send Server call in Node?
Install the "request" module with following command.

npm install request

Include the request module in page, and send the request to server.

request = require('request');
request( "http://exmaple.com:8081:/users/add/?n=test&p=2277585&email=test@gmail.com", function(err, res, body) {                    
          console.log(res);
          console.log(body);
      });

Question: How to post data and get in express Js?
HTML Code


<form action="http://example.com:8081/register" method="GET">
Name: <input name="name" type="text" />  <br />
Email: <input name="email" type="text" />
         Phone: <input name="phone" type="text" />
         <input type="submit" value="Submit" />
      </form>

Express JS Code

app.get('/register', function (req, res) {   
   response = {
      name:req.query.name,
      email:req.query.email
      phone:req.query.phone
   };
   console.log(response);
   res.end(JSON.stringify(response));
})

Question: How to get cookie in Express js?
Install the "cookie-parser" module with following command.

npm install cookie-parser

Include the cookie-parser, in node.

app.get('/', function(req, res) {
   console.log("Cookies: ", req.cookies)
})

Question: How Static Files works in Express js?
Static files are images/videos/css/js etc.
For this, first you need to set the folder path using "express.static" method. See Example

var express = require('express');
var app = express();
app.use(express.static('public'));
app.get('/', function (req, res) {
   res.send('Hello ');
});
var server = app.listen(8081, function () {
   var host = server.address().address
   var port = server.address().port
})

Question: How to upload images in Express js?
HTML Code


<form action="http://example.com:8081/file_upload" enctype="multipart/form-data" method="POST">
<input name="file" size="50" type="file" />         
         <input type="submit" value="Submit" />
      </form>

ExpressJS Code

var fs = require("fs");
var express = require('express');
var app = express();
var fs = require("fs");

app.post('/file_upload', function (req, res) {
   console.log(req.files.file.name);   
   var destinationFile = __dirname + "/images/" + req.files.file.name;
   
   fs.readFile( req.files.file.path, function (err, data) {
      fs.writeFile(destinationFile, data, function (err) {
         if( err ){
            console.log( err );
            }else{
               response = {
                  message:'File uploaded successfully in '+destinationFile,
                  filename:req.files.file.name
               };
            }
         //console.log( response );
         res.end( JSON.stringify( response ) );
      });
   });
})

Question: What are different methods in REST API?

GET : Used to read.
POST: Used to update.
PUT: Used to create.
DELETE: Used to delete

Question: How to setup the images and access them?
Add Following code in my server.js (OR main file).

app.use(express.static('public'))

Now, you can add images in public folder and can access like below:

http://localhost:3000/1.jpg
http://localhost:3000/2.jpg
http://localhost:3000/3.jpg

Question: How to do increment the value by 1?

 User.update({id: 100}, {$inc: { views: 1 }}).limit(1).exec();

Question: How to do decrement the value by 1?

 User.update({id: 100}, {$inc: { views: -1 }}).limit(1).exec();

Thursday, 1 September 2016

MongoDB Interview Questions and Answer for 1 Year Experienced

Question: Which field is Default Primary Key in MongoDB?

_id

_id is a 12 bytes hexadecimal number which is unique in every document(record).
Formation of 12 Bytes
4 bytes (for the current timestamp) + 3 bytes (for machine id) + 2 (bytes for process id) + 3 (increment value).

Question: Can we store Regular expression in MongoDB?
Yes, We can do.
For this there is data type i.e Regular expression.

Question: How to store array in MongoDB?
Yes, We can do.

db.mycollectiontest.insert(
{
   "_id": ObjectId(7df78ad8902c), 
   "url": "http://www.example.com",
   "tags": ["mongodb", "database", "NoSQL"],   
})

Question: What is syntax to update the document in collection?

db.collectiontest.update(SELECTIOIN_CRITERIA, UPDATED_DATA)

Question: How to remove one document in collection?

db.collectiontest.remove({'title':'title'},1)

Question: How to remove document based on search criteria?

db.collectiontest.remove({'title':'title'})

Question: How to use limit with search?

db.collectiontest.find({},{"title":1,_id:0}).limit(2)

Question: How to sort the documents?

->sort({"title":-1});

1: Ascending Order
-1: Descending Order

Question: What is Replication in MongoDB?
Replication is the process of synchronizing data across multiple servers.
Replication increases data availability with multiple copies of data on different database servers.

Question: How replication works in MongoDB?
A replica set is a "group of mongod instances" that host the same data set.
In a replica set one node is primary node and remaining nodes are secondary.
In a replica one node is primary node that receives all write operations.
All data replicates from primary to secondary node.

Question: What is Sharding?
Sharding is the process of storing data records across multiple machines to meeting the demands of data growth.

Question: What is Map-reduce?
Map-reduce is a data processing paradigm for condensing large volumes of data into useful aggregated results.

Question: What is a Covered Query?
It is query in which all the fields in the query are part of an index and all the fields returned in the query are in the same index.

Question: How to get new id of inserted New document?

$db->mycollectiontest->insert($data);
$newDocID = $data['_id'];

Question: How to Find a document with ObjectID in mongoDB?

$item = $collection->findOne(array(
    '_id' => new MongoId('4e49fd8269cb898c0a000000')));

Question: What is use of $explain operator in mongoDB?
$explain operator provides statistics on the query.
Use of query

db.mycollectiontest.find({gender:"F"},{user_name:1}).explain()

Question: How to Create New ObjectId in mongoDB?

newObjectId = ObjectId()

Question: How to ObjectId to String in mongoDB?

newObjectId.str

Question: What is use of $hint operator in mongoDB?
$hint operator forces the query to use the specified index to run a query.
Use of query

db.mycollectiontest.find({gender:"F"},{user_name:1}).hint({gender:1,user_name:1})

Question: What are the Limitations of Indexing?

A collection cannot have more than 64 indexes.
The length of the index name cannot be longer than 125 characters
A compound index can have maximum 31 fields indexed

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Friday, 7 July 2017

Mongoose iterate records over results using async module

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Monday, 5 June 2017

Mongoose Tutorial - listing records, Add Record, update record and delete record

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Tuesday, 30 May 2017

What is mongoose? How to use mongoose with nodejs for mongodb?

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Wednesday, 22 March 2017

Express js Interview questions and answers

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Thursday, 1 September 2016

MongoDB Interview Questions and Answer for 1 Year Experienced

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