September 2021

To get index lists

db.tableName.getIndexes()

To set Index

db.contact.createIndex({age:1})

It will create index in asc order

db.contact.createIndex({age:-1})

It will create index in desc order

db.contact.createIndex({age:1, gender:1})

Create group of index with age and gender both done in asc order.

To Delete Index

db.contact.dropIndex({"age": 1})

Value of key need to be 1 or -1 based on how index was created. If asc, 1 and for desc it is -1

Create Unique index

db.contact.createIndex({email:1},{unique: true})

Create Unique Index on email field. While inserting data one have to provide email field, else it would throw error

db.users.createIndex({email: 1}, {unique: true, partialFilterExpression: {email: {$exists: true}}})

Only create index for email field if exists. If field doesn't exists, no issue even while inserting new data.

TTL Index

db.sessions.createIndex({createdAt: 1}, {expireAfterSeconds: 10})

create index for CreatedAt (the column should be datetime type) and destroy the record having that index after 10 seconds.

db.users.updateOne({"_id" : ObjectId("11a")}, {$inc: {age: 2}})

Increment age by 2 for object id 11a

db.users.updateOne({"_id" : ObjectId("11a")}, {$inc: {age: -1}, $set: {exp: 22}})

Decrement age by 1 for object id 11a and set exp = 22

let assume a user Chris has age of 35

db.users.updateOne({name: "Chris"}, {$min: {age: 32}})

If age is more than 32, set age to 32. Chris age will change to 32

db.users.updateOne({name: "Chris"}, {$max: {age: 38}})

If age is less than 38, set age to 38. Chris age will change to 38 (as it was set to 32).

db.users.updateOne({name: "Chris"}, {$mul: {age: 1.1}})

Multiply age by 1.1

db.users.updateMany({isSporty: true}, {$unset: {phone: ""}})

Unset a field name phone. Need to provide an empty value to get it work.

db.users.updateMany({}, {$rename: {name: "FullName", age: "TotalAge"}})

Rename field named name to Full Name and age to Total Age.

db.users.updateOne({name: "Maria"}, {$set: {age: 26, hobbies: [{title: "Good food", frequency: 1}], isSporty: true}}, {upsert: true})

upsert as third param(Can be read as update or insert), can insert if not found, or if found it will update the value.

In above example, it will search for name Maria, if it exists it will update rest of the values, if it doesn't exisits, the new record will be created.

db.users.updateOne({name: "Maria"}, {$push: {hobbies: {title: "Sports", frequency: 2}}})

Push element with value if value exists, it will still add another element.

db.users.updateOne({name: "Maria"}, {$pull: {hobbies: {title: "Sports"}}})

Pull/Remove the element named Sports from hobbies

db.users.updateOne({name: "Maria"}, {$addToSet: {hobbies: {title: "Sports", frequency: 2}}})

Add element with value if value exists, it will not add add another element if value of the element is same. This is useful to avoid duplicate entry.

Fields

Array

Operators

Modifiers

Bitwise

db.users.find({}).sort({id: 1}).pretty()

.sort() with id in acending order

db.users.find({}).sort({id: -1}).pretty()

.sort() with id in decending order

db.users.find({}).sort({"ratings.average": -1}).pretty()

.sort() filter applied on average doocument/element under ratings with decending order

db.users.find({}).sort({"ratings.average": 1},{runtime: -1}).pretty()

.sort() in acending order by average ratings followed by runtime in decending order. eg. result will be like:

1) avgrating: 2, runtime 60 
2) avgrating: 2, runtime 40 
3) avgrating: 2, runtime 20 
4) avgrating: 4.1, runtime 60 
5) avgrating: 5, runtime 50 
6) avgrating: 5, runtime 40 
7) avgrating: 7.1, runtime 60

db.movies.find({}, {name: 1, _id: 0, "rating.average": 1, runtime: 1}).skip(10)

Skip first 10 result and show all result after 10th record

db.movies.find({}, {name: 1, _id: 0, "rating.average": 1, runtime: 1}).skip(100).limit(10)

Skip first 10 result and limit result to 10.

db.MoviesCollection.find({}, {genres: {$slice: 2}}).pretty()

Find all document but return only first two elements of genres in the result set.

db.MoviesCollection.find({}, {genres: {$slice: [1, 2]}}).pretty()

Find all document but return by skipping first element and display rest two elements of genres in the result set.