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Databases and Collections in MongoDB

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  • Overview
  • Databases
  • Collections

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.

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

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

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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:

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To learn more, see Connect to MongoDB.

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

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

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

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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.

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

A collection of MongoDB documents.
click to enlarge

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:

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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.

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

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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.

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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.

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

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.

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.

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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