Database
[{approvers:{tags:[{a:"1",b:"1",c:"3"},{a:"2",b:"3"}]}},{approvers:{tags:[{a:"1",b:"2"},{a:"2",b:"3"}]}},{approvers:{tags:[{a:"4",b:"4"},{a:"4",b:"5"},{a:"6",b:"7"}]}}]
Query
db.collection.find({"approvers.tags":{"$elemMatch":{$or:[{a:"1",b:"1"},{a:"4",b:"4"}]}}})