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