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Node.js - Node.JS and MongoDB.
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  Connecting To a Database

To connect to a mongo database from node application we require mongoose.

Installing Mongoose Go to the toot of your application and install mongoose by

npm install mongoose

Next we connect to the database.

var mongoose = require('mongoose');

//connect to the test database running on default mongod port of localhost  
mongoose.connect('mongodb://localhost/test');



//Connecting with custom credentials
mongoose.connect('mongodb://USER:PASSWORD@HOST:PORT/DATABASE');


//Using Pool Size to define the number of connections opening
//Also you can use a call back function for error handling
mongoose.connect('mongodb://localhost:27017/consumers', 
                 {server: { poolSize: 50 }}, 
                 function(err) {
                    if(err) {
                        console.log('error in this')
                        console.log(err);
                        // Do whatever to handle the error 
                    } else {
                        console.log('Connected to the database');
                    }
                });
  Inserting Documents

For inserting a new document in the collection, we create a object of the schema.

var Auto = require('models/auto')
var autoObj = new Auto({
    name: "NewName", 
    countOf: 10
});

We save it like the following

autoObj.save(function(err, insertedAuto) {
    if (err) return console.error(err);
    insertedAuto.speak();
    // output: Hello this is NewName and I have counts of 10
});

This will insert a new document in the collection
  Creating New Collection

With Mongoose, everything is derived from a Schema. Lets create a schema.

var mongoose = require('mongoose');
        
var Schema = mongoose.Schema;

var AutoSchema = new Schema({
    name : String,
    countOf: Number,
});
// defining the document structure 

// by default the collection created in the db would be the first parameter we use (or the plural of it)    
module.exports = mongoose.model('Auto', AutoSchema); 

// we can over write it and define the collection name by specifying that in the third parameters. 
module.exports = mongoose.model('Auto', AutoSchema, 'collectionName'); 


// We can also define methods in the models. 
AutoSchema.methods.speak = function () {
  var greeting = this.name
    ? "Hello this is  " + this.name+ " and I have counts of "+ this.countOf
    : "I don't have a name";
  console.log(greeting);
}
mongoose.model('Auto', AutoSchema, 'collectionName');

Remember methods must be added to the schema before compiling it with mongoose.model() like done above ..
  Reading

Reading Data from the collection is very easy. Getting all data of the collection.

var Auto = require('models/auto')
Auto.find({}, function (err, autos) {
      if (err) return console.error(err);
       // will return a json array of all the documents in the collection
      console.log(autos); 
})

Reading data with a condition

Auto.find({countOf: {$gte: 5}}, function (err, autos) {
      if (err) return console.error(err);
       // will return a json array of all the documents in the collection whose count is greater than 5
      console.log(autos); 
})

You can also specify the second parameter as object of what all fields you need

Auto.find({},{name:1}, function (err, autos) {
      if (err) return console.error(err);
       // will return a json array of name field of all the documents in the collection
      console.log(autos); 
})

Finding one document in a collection.

Auto.findOne({name:"newName"}, function (err, auto) {
      if (err) return console.error(err);
     //will return the first object of the document whose name is "newName"
      console.log(auto); 
})

Finding one document in a collection by id .

Auto.findById(123, function (err, auto) {
      if (err) return console.error(err);
     //will return the first json object of the document whose id is 123
      console.log(auto); 
})
  Updating

For updating collections and documents we can use any of these methods:

Methods

  • update()
  • updateOne()
  • updateMany()
  • replaceOne()

Update()

The update() method modifies one or many documents (update parameters)

db.lights.update(
   { room: "Bedroom" },
   { status: "On" }
)

This operation searches the 'lights' collection for a document where room is Bedroom (1st parameter). It then updates the matching documents status property to On (2nd parameter) and returns a WriteResult object that looks like this:

{ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 }

UpdateOne

The UpdateOne() method modifies ONE document (update parameters)

db.countries.update(
   { country: "Sweden" },
   { capital: "Stockholm" }
)

This operation searches the 'countries' collection for a document where country is Sweden (1st parameter). It then updates the matching documents property capital to Stockholm (2nd parameter) and returns a WriteResult object that looks like this:

{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }

UpdateMany

The UpdateMany() method modifies multible documents (update parameters)

db.food.updateMany(
   { sold: { $lt: 10 } },
   { $set: { sold: 55 } }
)

This operation updates all documents (in a 'food' collection) where sold is lesser than 10 *(1st parameter) by setting sold to 55. It then returns a WriteResult object that looks like this:

{ "acknowledged" : true, "matchedCount" : a, "modifiedCount" : b }

a = Number of matched documents
b = Number of modified documents

ReplaceOne

Replaces the first matching document (replacement document)

This example collection called countries contains 3 documents:

{ "_id" : 1, "country" : "Sweden" }
{ "_id" : 2, "country" : "Norway" }
{ "_id" : 3, "country" : "Spain" }

The following operation replaces the document { country: "Spain" } with document { country: "Finland" }

db.countries.replaceOne(
   { country: "Spain" },
   { country: "Finland" }
)

And returns:

{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }

The example collection countries now contains:

{ "_id" : 1, "country" : "Sweden" }
{ "_id" : 2, "country" : "Norway" }
{ "_id" : 3, "country" : "Finland" }
  Deleting

Deleting documents from a collection in mongoose is done in the following manner.

Auto.remove({_id:123}, function(err, result){
    if (err) return console.error(err);
    console.log(result); // this will specify the mongo default delete result.
});

Remarks

These are the basic CRUD operations for using mongo db with nodejs.

Question: Are there other ways you can do what is done here ??

Answer : Yes, there are numerous way to do this.

Question: Is using mongoose necessary ??

Answer : No. There are other packages available which can help you.

Question: Where can I get full documentation of mongoose ??

Answer: Click Here (opens new window)

 

Read Article
https://develop.horje.com/learn/1434/reference

 

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