MongoDB – Top 10 Most Common Commands for Beginners

Following is the list of these commands:

1. Login into MongoDB: Following command can be used to login into MongoDB database for a particular database. Make sure that the user with credentials such as username and password exists in the database mentioned in place of dbname.

   	mongo -u <username> -p <password> --authenticationDatabase <dbname>
   	

2. Show all databases: Once logged in as a user with appropriate role as userAdmin or userAdminAnyDatabase, one can see all the databases using command such as show dbs.
3. Select Database to work with: In order to start working with a particular database, the command such as use databaseName can be executed.
4. Authenticate and Logout from Database: When switching to different database using use dbName command, one would require to authenticate using a valid database user for that database. Following command can be used for authentication:

   	//
   	// Authenticate
   	//
   	db.auth("username", "password");
   	//
   	// Logout
   	//
   	db.logout()
   	

5. List Down Collections, Users, Roles etc.: Following commands can be used to check existing collections, users etc.

   	//
   	// List down collections of the current database
   	//
   	show collections;
   	db.getCollectionNames();
   	//
   	// List down all the users of current database
   	//
   	show users;
   	db.getUsers();
   	//
   	// List down all the roles
   	//
   	show roles
   	

6. Create a collection: Following command can be used to create a collection. The details on this command can be found on this page, Create Collection in a MongoDB database

   	db.createCollection("collectionName");
   	

7. Insert a Document in a Collection: Once a collection is created, next step is to insert one or more documents. Following is a sample command for inserting a document in a collection.

   	//
   	// Insert single document
   	//
   	db.<collectionName>.insert({field1: "value", field2: "value"})
   	//
   	// Insert multiple documents
   	//
   	db.<collectionName>.insert([{field1: "value1"}, {field1: "value2"}])
   	db.<collectionName>.insertMany([{field1: "value1"}, {field1: "value2"}])
   	

8. Save or Update Document: Following command, save, can be used to either update an existing document or insert a new one depending upon the document parameter passed to it. In case, the “_id” is passed matching an existing document, the document is updated. Otherwise, a new document is created. Internally, save method uses either insert or update command

   	//
   	// Matching document will be updated; In case, no document matching the ID is found, a new document is created
   	//
   	db.<collectionName>.save({"_id": new ObjectId("jhgsdjhgdsf"), field1: "value", field2: "value"}); 
   	

9. Display Collection Records: Following commands can be used to retrieve collection records:

   	//
   	// Retrieve all records
   	//
   	db.<collectionName>.find();
   	//
   	// Retrieve limited number of records; Following command will print 10 results;
   	//
   	db.<collectionName>.find().limit(10);
   	//
   	// Retrieve records by id
   	//
   	db.<collectionName>.find({"_id": ObjectId("someid")});
   	//
   	// Retrieve values of specific collection attributes by passing an object having 
   	// attribute names assigned to 1 or 0 based on whether that attribute value needs 
   	// to be included in the output or not, respectively.
   	//
   	db.<collectionName>.find({"_id": ObjectId("someid")}, {field1: 1, field2: 1});
   	db.<collectionName>.find({"_id": ObjectId("someid")}, {field1: 0}); // Exclude field1
   	//
   	// Collection count
   	//
   	db.<collectionName>.count();
   	

10. Administrative Commands: Following are some of the administrative commands which can be helpful in finding collection details such as storage size, total size, overall statistics.

    	//
    	// Get the collection statistics 
    	//
    	db.<collectionName>.stats()
    	db.printCollectionStats()
    	//
    	// Latency statistics for read, writes operations including average time taken for reads, writes
    	// and related umber of operations performed
    	//
    	db.<collectionName>.latencyStats()
    	//
    	// Get collection size for data and indexes
    	//
    	db.<collectionName>.dataSize() // Size of the collection
    	db.<collectionName>.storageSize() // Total size of document stored in the collection
    	db.<collectionName>.totalSize() // Total size in bytes for both collection data and indexes
    	db.<collectionName>.totalIndexSize() // Total size of all indexes in the collection