1. Mongo DB Terminologies

2. Managing Databases and Collections

• show dbs : shows you the name of your databases. This will only show output, when the db will have atleast one collection
• use <db name> : creates DB or switch DB
  • use college
• db.dropDatabase() : deletes the particular database
• db.createCollection('students') : creates students collection in college DB, here db. means students.
• db.<collection name>.insertOne({}) : inserting one row (document)
  • db.students.insertOne({name : "vikash", age : 21, profession : "btech"}) : inserting one row (document) in students collection.
• db.<collection name>.insertMany([ {}, {}, {} ]) : insert more than one row at once.
  • db.students.insertMany([ {name : "ashish", age : 43, profession : "finance"}, {name : "suman", age : 26, profession: "House wife"} ])

db.books.insertOne({
    title: "The Way of Kings", author: "Brandon Sanderson", rating: 9, pages: 400, genres: ["fantasy", "adventure"], reviews: [
        {name: "Yoshi", body: "Great book!!"},
        {name: "mario", body: "so so"}
    ]
})

• Ordered Insertion video
  • Ordered insertion means that MongoDB processes each document one by one.
  • If one document fails to insert due to an error (like a duplicate ID), MongoDB stops inserting further documents but keeps the ones that succeeded.
  • if there's a duplicate ID, MongoDB throws an error and stops inserting further documents.
  • we can change this behavior by setting "ordered" to false, allowing MongoDB to continue inserting documents after encountering an error.
  • db.<collection name>.insertMany([ {}, {}, {} ], {ordered : false})
  • Even if some documents fail to insert, the ones that succeeded remain in the collection.
  • They emphasize that once a document is successfully inserted, it won't roll back even if later documents encounter errors.

3. Search in DB

• db.students.find().pretty() : shows all the row of students collection in prettified format.
• db.students.find({name : "ashish", age : 43}).pretty() : find documents in students collection whose name : "ashish" and age : "43"
• db.students.find({age : {$gte : 50}}).count() : returns the count.
• db.students.find({age : {$gte : 50}}).limit(3) : this limits the number of document we get for particular filtered query.
• db.students.find({name : "ashish", age : {$lt : 50}}).pretty()
• db.students.find({name : "ashish", age : {$lte : 50}}).pretty()
• db.students.find({name : "ashish", age : {$gt : 50}}).pretty()
• db.students.find({name : "ashish", age : {$gte : 50}}).pretty()
• db.students.find({age : {$in : [12, 300, 9, 200]}}) : show all document which has age includes 12, 300, 9, 200
• db.students.find({age : {$nin : [12, 300, 9, 200]}}) : show all document which has age not includes 12, 300, 9, 200
• db.products.find({price: {$exists: true}}).count() : This will give us the documents having/not-having particular field.
• db.books.find({reviews : {$size : 2}}) : this will give me the books having 2 reviews
• db.students.find({math_score : {$type : 'int'}}).count() : This will give us the documents count having field of particular type. BSON types doc

Shows document fields of your choice [either give what to-show orelse what not-to-show, dont give both (_id is exception)]

• db.books.find({search query}, {fields to show / fields not-to show})
• db.books.find({ 'reviews': {$size:2}}, {title:1, author:1} : shows title and author only
• db.books.find({ 'reviews': {$size:2}}, {title:0, author:0} : shows other-field except title and author.

{
    _id: ObjectId("622b746cd28eddc86c808d41"),
    title: '1984',
    author: 'George Orwell',
    pages: 300,
    rating: 7,
    genres: [ 'sci-fi', 'dystopian', 'fantasy' ],
    reviews: [
        { name: 'luigi', body: 'not my cup of tea' },
        { name: 'mario', body: 'meh' }
    ],
    metadata: { views: 1500, likes: 60 }
}

• db.books.find().sort({ rating: 1 }) : sort ascending order of rating
• db.books.find().sort({ rating: -1 }): sort descending order of rating
• db.books.find({$or: [{rating: 7}, {rating: 9}]}) : we give array of filters, if anyone of the filters matches it print that document.
• db.books.find({$or: [{pages: {$lt: 300 }}, {pages: {$gt: 400}}]})
• db.books.find({$and: [{pages: {$gt: 500}}, {pages: {$lt: 1300 }}]}) : both condition should be true.
• db.books.find({genres: {$all: [fantasy", "sci-fi"]}})
  • we are finding books which has genres[] containing both(fantasy and sci-fi) atleast.
• db.books.find({genres: "fantasy"}) : this will find book which has genres as fantasy atleast.
• db.books.find({"reviews.name": "luigi"})
• db.books.find({"metadata.views": {$gt : 1200}})
• db.books.find({"reviews.name": "luigi", "metadata.views": {$gt : 1200}})
• db.books.find({'reviews.name': {$all: ['luigi', 'mario'] }

Itteration of document

db.<collection_name>.find().forEach(function(doc) {
    print("Key: " + doc.<key> + " Value: " + doc.<value>);
})

4. Update document in DB

• db.books.updateOne({_id: ObjectId("622b746cd28eddc86c808d40")}, {$set: {rating: 8, pages: 360}})
• db.books.updateMany({author: "Terry Pratchett"}, {$set: {author: "Terry Pratchet"}})
• db.books.updateOne({_id: ObjectId("622b746cd28eddc86c808d41")}, {$inc: {pages: 2}}) : increment the pages by 2.
• db.books.updateOne({_id: ObjectId("622b746cd28eddc86c808d41")}, {$inc: {pages: -2}}) : decrement the pages by 2.
• db.books.updateOne({_id: ObjectId("622b746cd28eddc86c808d41")}, {$pull: {genres: "fantasy"}}) : this will remove the "fantasy" from genres[]
• db.books.updateOne({_id: ObjectId("622b746cd28eddc86c808d41")}, {$push: {genres: "fantasy"}}) : this will add the "fantasy" in genres[]
• db.books.updateOne({_id: ObjectId("622b746cd28eddc86c808d41")}{$push:{genres: {$each: ["1","2"]}}}) : this will add more than one value in genres[]

5. delete documents in DB

• db.students.deleteMany({id : {$gt:2}})
• db.students.deleteMany({}) : delete all documents in students collection

6. Import/Export in mongoDB

• mongoimport <filePath\filename.json> -d <db name> -c <collection name> {}, {}, {}
• mongoimport products.json -d shop -c products --jsonArray if .json is [{} {} {}]

video reference