db={"users":[{_id:"5f1acd6e6985114f2c1567ea",name:"test user",email:"test@email.com"}],"talents":[{_id:"5f1acd6e6985114f2c1567fa",categoryId:"5f1acd6e6985114f2c1567ga",userId:"5f1acd6e6985114f2c1567ea",level:"5",}],"talent_media":[{_id:"5f1acd6e6985114f2c156710",talentId:"5f1acd6e6985114f2c1567fa",media:"file.jpg",fileType:"image"}],"categories":[{_id:"5f1acd6e6985114f2c1567ga",title:"java"}]}

db.users.aggregate([{$lookup:{from:"talents",let:{userId:"$_id"},pipeline:[{$match:{$expr:{$eq:["$$userId","$userId"]}}},{$lookup:{from:"categories",let:{categoryId:"$categoryId"},pipeline:[{$match:{$expr:{$eq:["$$categoryId","$_id"]}}},{$project:{_id:"",title:1}}],as:"categoryId"}},{$lookup:{from:"talent_media",let:{talentId:"$_id"},pipeline:[{$match:{$expr:{$eq:["$$talentId","$talentId"]}}},{$project:{_id:"",file:"$media",fileType:"$fileType"}}],as:"medias"}},{$unwind:{path:"$categoryId",preserveNullAndEmptyArrays:true}},{$project:{_id:"",categoryId:1,level:1,medias:1}}],as:"talents"}},{$project:{_id:"",email:1,name:1,talents:1}}])