As you know, it isn't possible to join different collections in MongoDB as it is in a typical relational database. Sometimes, this functionality is necessary and needs to be applied in other layers of your system. This is a gap in Pentaho Data Integration, and it was solved in a particular way by Ivy Information Systems in the same plugin that is mentioned in the previous recipe with the MongoDB Lookup step.
To get ready for this recipe, you will again need to start your ETL development environment Spoon. Make sure you have the MongoDB server running with the data from the previous chapters and the Ivy PDI MongoDB Steps plugin installed in the previous recipe.