Join two collections in MongoDB

Question

Am a beginner in mongoDB. I have two collections Book and author. [name and workswritten] are the common column respectively. Using inner join I have to emit the some columns in

Answer 1

You can compare below codes for SQL and mongoDB (NoSQL):

• SQL Code:

   SELECT *, [output array field]
        FROM collection
        WHERE [output array field] IN (SELECT *
              FROM [collection to join]
              WHERE [foreignField]= [collection.localField]);
  

• mongoDB (NoSQL):

   {
      $lookup:
        {
          from: [collection to join],
          localField: [field from the input documents],
          foreignField: [field from the documents of the "from" collection],
          as: [output array field]
        }
   }