Database IntegrationLesson 70Free preview

MongoDB Join

This lesson is part of Node.js · All levels

Summary

This lesson introduces $lookup, the way MongoDB combines a collection similar to JOIN in SQL. You'll pull the order data and user profiles into one pipeline aggregation. In addition to $lookup, there is $unwind available to unpack the join result array for easy processing.

Key points

$lookup is the aggregation stage of the collection combining from, localField, foreignField, and as.
After $lookup, the resulting field is an array (although only one match).
$unwind expands the resulting array to one row per element.
$project filters the column so the pipeline doesn't load large documents repeatedly.
$lookup with let/pipeline supports additional conditions (filtered lookup).

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