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We reference fields in the foreign collection with a single $. Notice how we use $$ to refer to the variables we defined in let. The examples are based on this sample data. We'll provide an example of each scenario. $lookup supports both basic equality matches as well as uncorrelated sub-queries. $lookup works by returning documents from a "joined" collection as a sub-array of the original collection. $lookup allows you to perform joins on collections in the same database. Working with Docker - Put your application in a Docker container for easy reuse and deployment.Preface: New to the aggregation pipeline? Check out our 5 minute explanation before diving into these $lookup examples.Īlso be sure to understand indexing and it's performance implications before reviewing these examples. #Mongodb compass project how to
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