exer6lookup.md

Lookup

• Left join for nosql

[
  {
    $lookup: {
      from: "authors",
      localField: "author_id",
      foreignField: "_id",
      as: "author_details"
    }
  },
  {
    $addFields: {
      author_details: {
        $arrayElemAt: ["$author_details", 0]
      }
    }
  }
]