[DATABASE - MONGO] Working with MongoDB Shell

I. Introduction

• mongo shell is an interactive JS interface to MongoDB.
• mongo shell uses commands to perform direct operations to the database such as query, update, etc...

II. Commands to work with mongo shell

1. Basic commands

• Open Command Prompt > type mongo command to open mongo shell.
• show dbs : shows all database you have.
• use databaseName: switches to the database if it exists, else create new database.
• db: shows the current database you are using.
• show collections: shows all collections in the current database.
• exit: exits the shell.

2. Adding new documents to a collection

• db.collectionName.insertOne({bson}): inserts one document at a time
• db.collectionName.insertMany([{bson}, {bson}]): insert many documents at a time

// opens userRelatedInfo database
use userRelatedInfo
// adds user named Vivian to the users collectoin 
db.users.insertOne(
  {
    name: "Vivian",
    sex: "Female"
  }
)

3. Finding documents

• db.collectionName.findOne({}): returns the first document in the collection.
• db.collectionName.findOne({field: "value", field1: "value"}): returns the first document matching the condition.
• db.collectionName.find()/find({}): lists the first 20 documents > it for more documents.
• db.collectionName.find({field: "value", field1: "value"}): returns all documents maching the condition.
• db.collectionName.find({condtion},{fieldName: 1, fieldName: 1}): returns documents maching the condition, arg2 to specified which field can be printed to the shell.

{ "_id" : ObjectId("64e13bdf6847f9e80d312d29"), "name" : "Vivian", "sex" : "Female", "rank":10 }

// finds user with name Vivian and only display her rank
db.users.find({"name": "Vivian"}, {rank: 1, _id: 0})

4. Sorting and limiting data

• db.collectionName.find(condition).count(): returns the number of matching documents.
• db.collectionName.find(condition).limit(number): prints only a number of document based on number specified.
• db.collectionName.find(condition).sort({field: number}): sorts the matching documents based on number specified, if number > 1, field is sorted in ascending order. if number < 1, it sorts in decending order.

5. Complex query with operators

• $gt, $lt, $lte, $gte

// finds all users whoes age is greater than 18
db.users.find( { "age": { $gt: 18 } } )

• $or

// matches users whose age is 18 or 19
db.users.find( {$or: [{age: 18}, {age: 19}] })

• $in: matches in range
• $nin: not matches in range

// matches users whose age is between 18-20
dbdb.users.find({ "age": {$in: [18,19,20]} })
// matches users whose age is less than 18 and greater than 20
dbdb.users.find({ "age": {$nin: [18,19,20]} })

• $inc: increases value
• $pull: takes out a value of an array
• $push: adds a new value to an array
• $each: loops

6. Deleting documents

• db.collectionName.deleteOne({field: value}): deletes the first document matching the condition.
• db.collectionName.deleteMany({condition}): deletes all documents matching the condition.

7. Updating documents

• db.collectionName.updateOne({name: "Vivian"}, {$set: {name: "Vivian Vu", rank: 8}}): finds the first document matching the condition then updates its value based on arg2.
• db.collectionName.updateMany({condition},{$set: {field1: newVal, field2, newVal}}): finds all matching documents then updates their values based on arg2.

III. Nested documents

1. Example

{
    name: "Wimpy Kid",
   author: {
       lastname: "Kinney",
       firstname: "Jeff" ,
   }
  genre: ["Comedy", "Fiction"],
  reader: [
      {name: "Vivian", age: 18},
      {name: "Irene", age: 20} 
  ]
}

1. Querying arrays

• { field : value } : value is the exact array to match, including the order of the elements.
• { array field: { operator1: value1, ... } }

// dress collection
 colors: ['red', 'black']
 // height collection
 heights: [10, 15.25]
 
 // match an array with exact order
db.dress.find({colors:['red','black']})

// match an array without exact order 
db.dress.find({colors: {$all: ['red','black'] }})

// query an array for an element
db.dress.find({colors: 'red' })
db.heights.find({ heights: {$gt: 10, $lt:12}})

// query an array by array length
db.heights.find({ heights: {$size: 3}})