The MongoDB Adapter supports joins of a nested array with its parent document.
Joining Nested Structures
The adapter expects the left part of the join is the array document you want to flatten vertically. This type of query is supported through the MongoDB API.
For example, consider the following query from MongoDB's restaurants collection:
SELECT "restaurants"."restaurant_id", "restaurants".name, "restaurants.grades".* FROM "restaurants.grades" JOIN "restaurants" WHERE "restaurants".name = 'Morris Park Bake Shop'See Vertical Flattening for more details.