db={"businesses":[{_id:ObjectId("5e3377bcb1dbae5124e4b6bf")},{_id:ObjectId("5e3377bcb1dbae5124e4b6c0")}],"users":[{business_account_id:ObjectId("5e3377bcb1dbae5124e4b6bf"),profile_id:ObjectId("5e3377bcb1dbae5124e4b6c1")},{business_account_id:ObjectId("5e3377bcb1dbae5124e4b6c0"),profile_id:ObjectId("5e3377bcb1dbae5124e4b6c2")}],"profile":[{_id:ObjectId("5e3377bcb1dbae5124e4b6c1"),type:"consultant"},{_id:ObjectId("5e3377bcb1dbae5124e4b6c2"),type:"owner"}]}

db.businesses.aggregate([{$match:{_id:{$in:[ObjectId("5e3377bcb1dbae5124e4b6bf"),ObjectId("5e3377bcb1dbae5124e4b6c0")]}}},{$project:{_id:1}},{$lookup:{from:"users",let:{"busId":"$_id"},as:"users",pipeline:[{$match:{$expr:{$eq:["$$busId","$business_account_id"]}}},{$lookup:{localField:"profile_id",from:"profile",foreignField:"_id",as:"profile"}},{$match:{"profile.type":"consultant"}}]}},{$project:{_id:0,business_account_id:"$_id",count:{$size:"$users"}}}])