How To Create Database In MongoDB

MongoDB didn’t provides any command to create “database“. Actually, you don’t need to create it manually, because, MangoDB will create it on the fly, during the first time you save the value into the defined collection (or table in SQL), and database.

For developer from SQL background, we need to create a database, table and insert values into table manually. In MongoDB, you don’t need to mention what you want to create, when first time you save the value into the defined collection (table), under selected database, MangoDB will create the value, collection and database automatically.

Note 
MongoDB contains “db.createCollection()” to create collection manually, but Not database.

In this guide, we will show you how and when MongoDB will create the database and collections.

1. Show all database

Issue “show dbs” to display all available databases.

MongoDB shell version: 1.8.1connecting to: test> show dbsadmin   0.03125GBlocal   (empty)

Currently, only two databases are available – “admin” and “local“.

2. Define a database name

Issue “use new-databasename” to switch from default database to define database (even non-exists database name will work). However, MangoDB doesn’t create any database yet, until you save something inside.

> use mkyongdbswitched to db mkyongdb> show dbsadmin   0.03125GBlocal   (empty)

P.S Database “mkyongdb” is not created yet.

3. Save It

Define a collection named “users“, and save a dummy document(value) inside.

> db.users.save( {username:"mkyong"} )> db.users.find(){ "_id" : ObjectId("4dbac7bfea37068bd0987573"), "username" : "mkyong" }>> show dbsadmin   0.03125GBlocal   (empty)mkyongdb        0.03125GB

This says, “save this document (value) ‘{username:"mkyong"}‘ into the ‘user’ collection”. When this “save” operation is performed, MangoDB will create the “user” collection, and “mkyongdb” database automatically.

转载源地址：http://www.mkyong.com/mongodb/how-to-create-database-or-collection-in-mongodb/