Database
db={"A":[{"item":"Kitchen","location":"New York","ids":[ObjectId("5f6dce24021e15a1121a649a"),ObjectId("5f6dce24021e15a1121a649b"),ObjectId("5f6dce24021e15a112a649c1")]},{"item":"Bathroom","location":"New York","ids":[ObjectId("5f6dce24021e15a112a649c1")]},{"item":"Living Room","location":"New York","ids":[ObjectId("5f6dce24021e15a1121a649a"),ObjectId("5f6dce24021e15a1121a649b")]}],"B":[{"_id":ObjectId("5f6dce24021e15a1121a649a"),"name":"George","Age":12,"Nationality":"English"}]}
Query
db.A.aggregate([{$match:{ids:ObjectId("5f6dce24021e15a1121a649a")}},{$group:{_id:null,items:{$push:"$item"}}}])