Hướng dẫn mongodb lookup multiple collections
According to the documentation, $lookup can join only one external collection. Show What you could do is to combine Please find below 2-step query, which combines userInfo with userRole - creating new temporary collection used in last query to display combined data. In last query there is an option to use $out and create new collection with merged data for later use.
I have two collections, I'm doing a lookup such as:
This is basically getting me all of the products that match the category_id and including the properties that match the same category_id. I need to add an additional check, for any idea how I could this? Docs Home → MongoDB Manual On this page
$lookup Changed in version 5.1. Performs a left outer join to a collection in the same database to filter in documents from the "joined" collection for processing. The Starting in MongoDB 5.1, To combine elements from two different collections, use the The To perform an equality match between a field from the input documents with a field from the documents of the "joined" collection, the
The
The operation would correspond to the following pseudo-SQL statement:
See these examples:
MongoDB 3.6 adds support for:
In MongoDB, a correlated subquery is a pipeline in a NoteStarting in MongoDB 5.0, for an uncorrelated subquery in a MongoDB correlated subqueries are comparable to SQL correlated subqueries, where the inner query references outer query values. An SQL uncorrelated subquery does not reference outer query values. MongoDB 5.0 also supports concise correlated subqueries. To perform correlated and uncorrelated subqueries with two collections, and perform other join
conditions besides a single equality match, use this
The
pipeline Specifies the The The NoteTo reference variables in pipeline stages, use the The let variables can be accessed by the stages in the pipeline, including additional
as Specifies the name of the new array field to add to the joined documents. The new array field contains the matching documents from the joined collection. If the specified name already exists in the joined document, the existing field is overwritten. |