{"id":104145,"date":"2024-10-16T18:02:50","date_gmt":"2024-10-16T18:02:50","guid":{"rendered":"https:\/\/www.red-gate.com\/simple-talk\/?p=104145"},"modified":"2024-11-14T22:03:45","modified_gmt":"2024-11-14T22:03:45","slug":"creating-views-in-mongodb","status":"publish","type":"post","link":"https:\/\/www.red-gate.com\/simple-talk\/databases\/nosql\/mongodb\/creating-views-in-mongodb\/","title":{"rendered":"Creating Views in MongoDB: Aggregation Pipelines, $lookup Joins, On-Demand Materialised Views, and MongoDB Compass"},"content":{"rendered":"

This article is part of Robert Sheldon's continuing series on Mongo DB. To see all of the items in the series, click here<\/a>.<\/strong><\/p>\n\n

Like many relational database systems, MongoDB supports the use of views. A view is a read-only object in a MongoDB database that works much like a collection<\/a>, except that the data is not persisted to disk. MongoDB retrieves the view\u2019s documents from the source collection when a client calls the view. In this sense, a view is essentially a saved query that MongoDB runs at the time the view is invoked.<\/p>\n

This article, which is part of a series on MongoDB, introduces you to views and how you can create, query, and update them. It also includes a number of examples that demonstrate how they work. The article focuses exclusively on standard views, which are one of two types of views in MongoDB. The platform also supports on-demand materialized views that persist data to disk. However, materialized views are beyond the scope of this article. For now, we\u2019ll stick with standard views, which is a good place to start when learning about views.<\/p>\n

Note: For the examples in this article, I used the same MongoDB Atlas and MongoDB Compass environments I used for the previous articles in this series. Refer to the first article for details about setting up these environments. The examples require the <\/em>hr<\/em><\/code> database and <\/em>candidates<\/em><\/code> collection, which were used in previous articles. If you haven\u2019t set them up, you should do so now, assuming you want to try out the examples in this article.<\/em><\/p>\n

Introducing views in MongoDB<\/h2>\n

Adding a view to a MongoDB database is a fairly straightforward process. You can use either MongoDB Shell or the MongoDB Compass interface. For this article, I focus primarily on running commands in MongoDB Shell, although I provide an overview of the GUI approach later in the article.<\/p>\n

To create a view in MongoDB Shell, you can use either the createView<\/code> or createCollection<\/code> database method. I\u2019ve used the createView<\/code> method in the examples here because I like the fact that the name clearly telegraphs what you\u2019re trying to achieve. If you want to learn how to use the createCollection<\/code> method, refer to the MongoDB article db.createCollection()<\/a>.<\/p>\n

When you create a view in MongoDB, you must define an aggregation pipeline that determines which documents to return when a client queries the view. You must also provide a name for a view, as well as the source collection, as shown in the following syntax:<\/p>\n

db.createView(\n  \"<view_name>\",\n  \"<source_collection>\",\n  [<pipeline>],\n  { \"collation\" : { <settings> } }\n)<\/pre>\n
In MongoDB, a createView<\/code> method consists of the following components:<\/p>\n