mongodb.md

#MongoDB commands

###General commands

• To start the server process

    mongod
  

• To start the mongo shell

    mongo
  

• To import collections

    mongoimport
  

---

###CRUD ####Creating Documents

• Insert a single document

     db.movies.insertOne({title: 'Rocky', rating: 7.8, imdb: 't1235'});
  

_id field will be automatically generated, we can override by passing _id field

• Insert many documents

    db.movies.insertMany([{title: 'Rocky', rating: 7.8, imdb: 't1235'}, {title: 'Rocky2', rating: 7.5, imdb: 't1233'}], {ordered: false});
  

• array of documents should be passed to insertMany

• second argument ordered attribute

• If ordered true, then insert operation will stop with the first error.

####Reading Documents

• Finding a document

    db.movies.findOne();
    db.movies.find();
  

• Findig document using conditions

    db.movies.findOne({rated: "PG-13"});
    db.movies.find({rated: "PG-13"});
  
    db.movies.find({rated: "PG-13", year: 2008});
    
    //For specifing nested property - Don't forget quotes
    db.movies.find({"tomato.meter": 80});
    
    /*For finding documents based on array elements*/
  
    //To match the documents having exact same array
    db.movies.find({"authors": ["Ethan Coen", "Joel Coen"]});
  
    //To match the documents having the element in any position in array
    db.movies.find({"actors": "Tom Hanks"});
  
    //Based on specific position in the array - starts with index 0
    db.movieDetails.find({"actors.0": "Claudia Cardinale"})
  

• Filter document properties in output using projection

    /*Projection - filter the output properties of document*/
    // Second argument - denotes projection
    //1 - include; 2 - don't include
    
    // Just remove title from the output
    db.movies.find({"actors": "Tom Hanks"}, {title: 0});
    // Show title, remove all other properties from output - but _id will be included
    db.movies.find({"actors": "Tom Hanks"}, {title: 1});
    // Show title, remove all other properties(including _id) from output 
    db.movies.find({"actors": "Tom Hanks"}, {title: 1,_id: 0});
  

Comparision operators

	/** General syntax of comaprision operators  **/
	/** field : {$operator : value} **/
	/** field : {$operator : [value1, value2]} //For $in, $nin **/

	db.movieDetails.find({runtime: {$gt : 50}});
	db.movieDetails.find({runtime: {$gt : 50, $lte : 80}});
	db.movieDetails.find({"tomato.meter" : {$gt :50},runtime: {$gt : 50, $lte : 80}});
	db.movieDetails.find({rated: { $ne : "UNRATED"}});
	db.movieDetails.find({rated: { $in : ["PG", "PG-13", "R"]}});

Element operators

	//To match based on element's existence or non-existence
	db.movieDetails.find({"tomato.meter" : {$exists : false}});
	db.movieDetails.find({"tomato.meter" : {$exists : false}});
	//To match based on type of elements
	db.movieDetails.find({_id : {$type : "objectId"}});
	db.movieDetails.find({_id : {$type : "string"}});

Logical operators

	// or operator
	db.movieDetails.find({ $or : [{"tomato.meter" : {$gt :50}},{runtime: {$gt : 50, $lte : 80}}]});
	// and operator for different fields are implicit by , 
	// ie, below two queries fetch same result.
	db.movieDetails.find({"tomato.meter" : {$gt :50},runtime: {$gt : 50, $lte : 80}});
	db.movieDetails.find({ $and: [{"tomato.meter" : {$gt :50}},{runtime: {$gt : 50, $lte : 80}}]});
	db.movieDetails.find({"tomato.meter" : {$exists : true, $ne : null}});

Regex operator

	db.movieDetails.find({ "awards.text" : { $regex: /^Won.*/}});

Array operators

	//To check the array contains all the mentioned values.
	//ie, the array can contain these values in any order along with other values too
	db.movieDetails.find({genres :{$all :["Comedy","Crime","Drama"]}});

	//To match the sizeof array
	db.movieDetails.find({genres: {$size :2}});

	//To match the complex element in the array against multiple conditions.

	//lets say documents contains field boxOffice like below,
	//boxOffice: [{country: "UK",value: 50},{country: "US",value: 20}]
	//To match documents having boxoffice in UK and value >30
	db.movieDetails.find({boxOffice: {$elemMatch: {country: "UK", value : {$gt: 30}}}});

Helper methods.

• count() - To count the resultset
• pretty() - To pretty print the resultset in shell

##Advanced Topics

######Object Id ObjectId format = 12 byte HEX string

DATE	MAC_ADDR	PID	COUNTER
4	3	2	3

######Cursor

find() method returns the cursor.

cursor has below methods.

• hasNext()
• next()