$lookup

Aggregation $lookup

This aggregation stage performs a left outer join to a collection in the same database.

There are four required fields:

• from: The collection to use for lookup in the same database
• localField: The field in the primary collection that can be used as a unique identifier in the from collection.
• foreignField: The field in the from collection that can be used as a unique identifier in the primary collection.
• as: The name of the new field that will contain the matching documents from the from collection.

Example

db.comments.aggregate([
  {
    $lookup: {
      from: "movies",
      localField: "movie_id",
      foreignField: "_id",
      as: "movie_details",
    },
  },
  {
    $limit: 1
  }
])

This will return the movie data along with each comment.