MongoDB

index

In Node.js :

.find() returns a cursor so use .find().forEach()

MONGOOSE :

         --> Collection C1 --> { Documnets ==> D1 , D2 , D3 }
DataBase --> Collection C2 --> { Documnets ==> D1 , D2 , D3 }
         --> Collection C3 --> { Documnets ==> D1 , D2 , D3 }

Every Collection on MongoDB ==> Every Model in Mongoose 
Schema in Mongoose define schema of documents on MongoDB

Connecting to Mongo By Mongoose :

const mongoose = require('mongoose');
 
const MONGO_URL = "mongodb+srv:// something ....";
 
await mongoose.connect(MONGO_URL,{})
.catch(err => console.log(err))
.then(() => console.log("connected to DB"));
console.log("after connection");
 
// Below is code add event listener :
mongoose.connection.on('error', err => {
	console.error(err);
});

Schema and Model in Mongoose :

refer : Mongoose v8.3.3: Schemas (mongoosejs.com)

const mongoose = require('mongoose');
 
const planetSchema = new mongoose.Schema({
   kepler_name : {
        type : String,
        required: true
   }
})
 
module.exports = mongoose.model('Planet', planetSchema);
// so here instead of Planet name as collection planets
// will be added to mongodb

Manipulating Data in Docs :

Note : UPSERT (Update if found, Insert new doc if not found)

updateOne() function also add $setOnInsert property which can reveal that we are using MongoDB upsert, to avoid this use findOneAndUpdate() function.

await planets.updateOne(
	{find_by_field : old_data} ,
	{field_to_be_changed : new_data} ,
	{upsert: true}
);
 
// UPSERT ==> Update + Insert
// Update if found, Insert new doc if not found

Note : __v value is added by Mongoose

// (A document in MongoDB)
{
	"_id": ObjectId('6638dc913b33276166ad43b4'),
	"field":"data",
	"__v": 0
}

here __v is version key ==> version of document we created
if we change schema and want old and new data to persist then 
we can increase __v value differentiating new docs.

MongoDB Queries :

Manipulating Docs of Collection :

• db.collection_name.insertOne({ something in json format }) to insert a single json object in form of document

NOTE :: MongoDB automatically adds an ObjectId to each document

• db.collection_name.insertMany([{ something in json format } ,{ something in json format } ,{ something in json format } ,{ something in json format } .....]) to insert a single json object in form of document
• db.collection_name.find() to grab all documents
• db.collection_name.find( {field1 : "value" , field2 : "value"} ) to grab filtered documents according to given field/s and its value/s

NOTE : let numbers1: [{1} ,{2} ,{3}] and numbers2: {1} then .find({numbers: "1" }) will return numbers1 and numbers2 documents but if we do query such as .find( {numbers : ["1"] } ) returns numbers2 document only

• db.collection_name.find( {field1 : "value" , field2 : "value"} , {field_required1 : 1 , field_required2 : 1} ) to grab filtered documents according to given field/s and its value/s and to show only field_required field of each filtered document
• db.collection_name.find( {field1 : "value"} ).count() to grab filtered documents according to given field/s and its value/s and return only number of such documents
• db.collection_name.find( {field1 : "value"}).limit(n) to grab filtered documents according to given field/s and its value/s and to show only first “n” documents
• db.collection_name.find().sort( {field : 1} ) to grab documents in ascending sorted form according to given field
• db.collection_name.find().sort( {field : -1} ) to grab documents in descending sorted form according to given field

Query Operators :

• to load query such as greater than $gt,greaterthanequalto$gte use dollar sign and always use a query inside curly brackets

Greater or lesser operator

• db.collection_name.find( {rating: {$gt:7} } ) query for greater than 7
• db.collection_name.find( {rating: {$lt:7} } ) query for lesser than 7
• db.collection_name.find( {rating: {$gte:7} } ) query for greater than or equal to 7
• db.collection_name.find( {rating: {$gte:7} } ) query for lesser than or equal to 7

OR operator

• db.collection_name.find( {$or: [{rating:7} , {rating:9}] ) query for rating: 7 or rating: 9

IN operator and NOT IN operator (for range of value)

• db.collection_name.find( {rating: {$in: [7,8,9] }} ) query for rating: 7 or rating:8 or rating: 9
• db.collection_name.find( {rating: {$nin: [7,8,9] }} ) query for documents which don’t have rating: 7 or rating:8 or rating: 9

ALL operator

• let numbers1: [{1} ,{2} ,{3}] and numbers2: {1} then .find({numbers: {$all: ["1","2"]} }) will return numbers1 , it checks if the given field atleast contains the given values

Nested Documents :

• let details:{ name:"XYZ" , email:"xyz@gmail.com" , age :"30"} then to find name XYZ use .find({ "details.name" : "XYZ" })

Deleting Docs of Collection :

• db.collection_name.deleteOne({ field: "value" }) to delete a single json object in form of document
• db.collection_name.deleteMany({ field: "value" }) to delete multiple documents according to field

Update Docs of Collection :

• db.collection_name.updateOne({ field_to_find: "value" } , {$set: {field_1_to_be_updated : "new_value_1" , field_2_to_be_updated : "new_value_2"}}) to update a document which contain “field_to_find” field with value = value and set “field_to_be_updated” field to its new value
• db.collection_name.updateMany({ field_to_find: "value" } , {$set: {field_1_to_be_updated : "new_value_1" , field_2_to_be_updated : "new_value_2"}}) to update all document which contain “field_to_find” field with value = value and set “field_to_be_updated” field to its new value

Note : UPSERT (Update if found, Insert new doc if not found)

await planets.updateOne(
	{kepler_name : data.kepler_name} ,
	{kepler_name : data.kepler_name} ,
	{upsert: true}
);
 
// UPSERT ==> Update + Insert
// Update if found, Insert new doc if not found

Extra bits :

INC (increment) operator $inc:ntoincrementor$inc: -n to decrement

• db.collection_name.updateOne({ field_to_find: "value" } , {$inc: {field_to_be_updated : n }) to increment a value by n in a document which contain “field_to_find” field with value = value and set “field_to_be_updated” field to its new value

PULL (to remove an element from array)

• db.collection_name.updateOne({ field_to_find: "value" } , {$pull: {array : "element_to_be_removed" }) to remove element_to_be_removed from an array where there is a “field_to_find” field with value = value

PUSH (to add an element from array)

• db.collection_name.updateOne({ field_to_find: "value" } , {$push: {array : "element_to_be_added" }) to add element_to_be_added to an array where there is a “field_to_find” field with value = value

EACH (add or remove multiple elements of an array)

• db.collection_name.updateOne({ field_to_find: "value" } , {$push: {array : {$each: ["element1","element2","element3"]} }) to add element1 2 3 to an array where there is a “field_to_find” field with value = value

IN TERMINAL :

Start terminal :

Type mongosh to enter mongodb shell

Basic commands :

• cls to clear terminal
• show dbs to see all databases
• db to show all collections of database you are in
• help for help
• exit to exit
• use database_name to move to database_name database
• use database_name then db.collection_name to move to collection_name collection