db={"users":[{"_id":"5f1eef8ec68d306fbbf13b0f","name":"John Davis","email":"John@gmail.com","__v":0},{"_id":"9q1eef8ec68d306fbbf13bh6","name":"Mik Luca","email":"Mik@gmail.com","__v":0}],"usersProfile":[{"_id":"5f1eef8ec68d306fbbf13b10","other_skills":[null],"user_id":"5f1eef8ec68d306fbbf13b0f","phone_number":"1234569870","location":"5f16b72617fee02922688751","primary_skills":[{"_id":"5f32635cf764cc40447503a6","years":1,"skill_id":"5f0da75907a96c3040b3667d"}]},{"_id":"5f1eef8ec68d306fbbf13b11","other_skills":[null],"user_id":"9q1eef8ec68d306fbbf13bh6","phone_number":"1234569870","location":"5f16b72617fee02922688751","primary_skills":[{"_id":"6s0da75907a96c3040b36690","years":1,"skill_id":"5f0da75907a96c3040b3667d"}]}],"skills":[{"_id":"5f0da75907a96c3040b3667d","skill":"Mongo"},{"_id":"6s0da75907a96c3040b36690","skill":"Node"}]}

db.users.aggregate([{$lookup:{from:"usersProfile",let:{id:"$_id"},as:"userProfiles",pipeline:[{$match:{$expr:{$eq:["$$id","$user_id"]},"primary_skills.skill_id":"5f0da75907a96c3040b3667d"}},{$unwind:"$primary_skills"},{$lookup:{from:"skills",localField:"primary_skills.skill_id",foreignField:"_id",as:"primary_skills.skill_id"}},{$unwind:"$primary_skills.skill_id"},{$group:{_id:"$_id",other_skills:{$first:"$other_skills"},phone_number:{$first:"$phone_number"},location:{$first:"$location"},primary_skills:{$push:{_id:"$primary_skills._id",skill:"$primary_skills.skill_id.skill",years:"$primary_skills.years"}}}}]}},{$match:{userProfiles:{$ne:[]}}}])