Database
[{"_id":12345,"orderItems":[{"itemId":45678,"isAvailable":true,"isEligible":false},{"itemId":87653,"isAvailable":true}]},{"_id":12346,"orderItems":[{"itemId":45678,"isAvailable":true,"isEligible":false},{"itemId":87653,"isAvailable":true,"isEligible":true}]},]
Query
db.collection.find({orderItems:{$elemMatch:{"isEligible":{$exists:false}}}},{_id:1})