> intorductioon
mongod is a database server , this should be up and running
mongod --port = PORT will be running mongo server on perticular server
mongo is a mongoDB shell , this is used to do all mongo operation , thought we haave DRIVERS for all kind of platform

Shell command are almost similar as JAVAscript driver for nodejs

show dbs > show databases
use DataBase_name > create a database
db.collectionName.insertOne({JSON_Document}) > create a collection and inserting a document into it

 > CRUD operations
 Create : insertOne(data,options) , insertMany(data,options)
 Read   : find(filter,options), findOne(filter,options)
 Update : updateOne(filter,data,options) , updateMany(filter,data,options), replaceOne(filter,data,options)
 Delete : deleteOne(filter,options), deleteMany(filter,options)

 UpdateMany({},{$set : {marker:"delete"}}) this will set field in all dcuments as FILTER is {}
 DelateMany({}) This will delete all data

 Above two will only work with Many() operations

 >Finding
 options can contain matching key value pair
 Note :*
 [
  {
    "departureAirport": "MUC",
    "arrivalAirport": "SFO",
    "aircraft": "Airbus A380",
    "distance": 12000,
    "intercontinental": true
  },
  {
    "departureAirport": "LHR",
    "arrivalAirport": "TXL",
    "aircraft": "Airbus A320",
    "distance": 950,
    "intercontinental": false
  }
]

db.flightData.find({distance: {$gt:1000}})
** $gt is greater than symbol , similarly we have $lt //// in update we had $set

> Update
in update we saw we had updateOne(), updateMany(),ReplaceOne() BUT we have update()
this do not take $set key , it takes entire object and replace existing contentt with new object

> Find
when we write a find query it return a cursor which is a iterator on data list
when we type "it" it send new set of data
to convert data recieved from find we need function as follows
db.passengers.find().toArray()   >>> this will return entire array

forEach()
db.passengers.forEach((data)=>printjson(data))

*note here find is returning a cursor , nwo the inbuild method forEach is accessing cursor to get data one by one
so it is very efficient , it do not access entire data in one shot , it iterate over a cursor


 >PROJECTION
 when we query data from database we get unnecessory data along with required data like some extra fileds
 and we filter out those extra fields in out application In almost all programming language
 here comes the concept of projection , this removes unneessory data at mongodb server

 we get data by using find()
 now we add projection to find by adding an object as a second parameter
 db.passenges.find({},{name:1,_id:0}) // this will remove id as well , this is a explicit call to remove _id
 with help of projection we can save network bandwidth

 > Embeded documents
 documents within document , there is a limit of nesting document till 100 levels and maximum size of a document can be 16 MB

 >Array in documents
 an array can be part of a documents , this arraya can contain a document , a number , a string

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