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Introduction

Databases and Collections in MongoDB

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  • Overview
  • Databases
  • Collections

Overview

MongoDB stores data records as documents (specifically BSON documents) which are gathered together in collections. A database stores one or more collections of documents.

You can manage databases and collections on the Atlas cluster from the Atlas UI, mongosh, or MongoDB Compass. This page describes how to manage databases and collections on the Atlas cluster from the Atlas UI. For self-managed deployments, you can use mongosh or MongoDB Compass to manage databases and collections.

Select the client that you want to use to manage databases and collections.

MongoDB Atlas is a multi-cloud database service that simplifies deploying and managing your databases on the cloud providers of your choice.

The MongoDB Shell, mongosh, is a JavaScript and Node.js REPL environment for interacting with MongoDB deployments. To learn more, see mongosh.

MongoDB Compass is a powerful GUI for querying, aggregating, and analyzing your MongoDB data in a visual environment. To learn more, see MongoDB Compass.

Databases

In MongoDB, databases hold one or more collections of documents.

To select a database to use, log in to Atlas and do the following:

1

Navigate to the Collections tab.

2

Select the database from the list of databases in the left pane.

To select a database to use, in mongosh, issue the use <db> statement, as in the following example:

use myDB

To select a database to use, complete the following steps:

1

Start MongoDB Compass and connect to your cluster.

To learn more, see Connect to MongoDB.

2

Select Databases from the left navigation.

The Databases tab opens to list the existing databases for your MongoDB deployment.

Create a Database

To create a new database, log in to Atlas and do the following:

1

Navigate to the Collections tab.

2

Click Create Database.

3

Enter the Database Name and the Collection Name.

Enter the database and the collection name to create the database and its first collection.

4

Click Create.

Upon successful creation, the database and the collection displays in the left pane in the Atlas UI.

If a database does not exist, MongoDB creates the database when you first store data for that database. As such, you can switch to a non-existent database and perform the following operation in mongosh:

use myNewDB
db.myNewCollection1.insertOne( { x: 1 } )

The insertOne() operation creates both the database myNewDB and the collection myNewCollection1 if they do not already exist. Be sure that both the database and collection names follow MongoDB Naming Restrictions.

1

Open the Databases tab.

2

Click the Create database button.

3

Enter database and first collection names in the Create Database dialog.

4

Click Create Database to create the database and its first collection.

Collections

MongoDB stores documents in collections. Collections are analogous to tables in relational databases.

A collection of MongoDB documents.
click to enlarge

Create a Collection

If a collection does not exist, MongoDB creates the collection when you first store data for that collection.

To create a new collection, log in to Atlas and do the following:

1

Navigate to the Collections tab.

2

Click the + icon for the database.

3

Enter the name of the collection.

4

Click Create.

Upon successful creation, the collection displays underneath the database in the Atlas UI.

db.myNewCollection2.insertOne( { x: 1 } )
db.myNewCollection3.createIndex( { y: 1 } )

Both the insertOne() and the createIndex() operations create their respective collection if they do not already exist. Be sure that the collection name follows MongoDB Naming Restrictions.

1

Click the name of the database where you to want to create a collection in the left navigation.

2

Click the + icon next to the database name.

3

Enter the name of the collection in the Create Collection dialog.

4

Click Create Collection to create the collection.

Explicit Creation

To create a new collection, log in to Atlas and do the following:

1

Navigate to the Collections tab.

2

Click the + icon for the database.

3

Enter the name of the collection.

4

Optional. From the Additional Preferences dropdown, select the type of collection that you want to create.

You can create one of the following types of collections:

  • Capped collection

    If you select to create a capped collection, specify the maximum size in bytes.

  • Time Series Collection

    If you select to create a time series collection, specify the time field and granularity. You can optionally specify the meta field and the time for old data in the collection to expire.

  • Clustered Index Collection

    If you select to create a clustered collection, you must specify clustered index key value and a name for the clustered index.

5

Click Create.

Upon successful creation, the collection displays underneath the database in the Atlas UI.

MongoDB provides the db.createCollection() method to explicitly create a collection with various options, such as setting the maximum size or the documentation validation rules. If you are not specifying these options, you do not need to explicitly create the collection since MongoDB creates new collections when you first store data for the collections.

To modify these collection options, see collMod.

1

Click the name of the database where you to want to create a collection in the left navigation.

2

Click the Create collection button.

3

Enter the name of the collection and optionally, configure additional preferences.

4

Click Create Collection to create the collection.

MongoDB Compass provides the following additional preferences that you can configure for your collection:

Document Validation

By default, a collection does not require its documents to have the same schema; i.e. the documents in a single collection do not need to have the same set of fields and the data type for a field can differ across documents within a collection.

However, you can enforce document validation rules for a collection during update and insert operations. See Schema Validation for details.

For deployments hosted in MongoDB Atlas, the Performance Advisor and the MongoDB Atlas UI detect common schema design issues and suggest modifications that follow MongoDB best practices. To learn more, see Schema Suggestions.

Modifying Document Structure

To change the structure of the documents in a collection, such as add new fields, remove existing fields, or change the field values to a new type, update the documents to the new structure.

Unique Identifiers

Collections are assigned an immutable UUID. The collection UUID remains the same across all members of a replica set and shards in a sharded cluster.

To retrieve the UUID for a collection, run either the listCollections command or the db.getCollectionInfos() method.

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