#Mongodb compass join two collections how to
#Mongodb compass join two collections code

#Mongodb compass join two collections how to

In this article, we provided a basic overview of the $lookup function in MongoDB and walked through some examples of how to use the function. If you design a whole schema around a schemaless data. When you need to join two MongoDB collections and retrieve fields from documents stored in both of them, the $lookup function can help you target the right data and get the results you want. When you use lookup you are performing a join on two different collections.

#Mongodb compass join two collections code

'_id' : ObjectId ( '5e2934cdbf4122213c8171a1' ), For example we can return the student name, units this student is doing and the number of tournaments played using multiple JOINS with the code below: SELECT students.name, ades, sports.tournamentsPlayed FROM students INNER JOIN units ON students.id units.id INNER JOIN sports ON students.id sports.id WHERE students. Let’s begin by creating a sample dataset that we can use in our examples: On the Documents page, click Aggregation. We now merge the two collections using the aggregation function. We created two collections for genera and movies in the test database, and we also inserted some documents into both collections. We’d want to do this in a single query to simplify the code and reduce data transactions between the client and the database. Image Source If desired, create a new collection and database. We want to retrieve a list of all the users and show a list of the products they have each bought. This function can handle both uncorrelated sub-queries and equality matches. Imagine we have two collections: a collection of users and a collection of products.

The $lookup function will return the documents as if they came from this ‘joined’ collection, in the form of a sub-array of the target original collection. $lookup OverviewĪs we mentioned earlier, the $lookup function in MongoDB allows us to join documents on collections that reside in the same database. Prerequisiteīefore proceeding with this tutorial, be sure that MongoDB is installed and configured on your machine. In this tutorial, we’ll take a closer look at the $lookup function in MongoDB and check out some examples of how it’s used. The $lookup function makes it easy to “join” multiple collections, returning results that contain fields from all specified collections.

When you’re querying data in MongoDB, there are times when you need information that’s stored in documents across multiple collections.