db={"matches":[{date:"2020-02-15T17:00:00Z",players:[{_id:"5efd9485aba4e3d01942a2ce"},{_id:"5efd9485aba4e3d01942a2cf"}]},],"players":[{_id:"5efd9485aba4e3d01942a2ce",name:"Rafa Nadal"},{_id:"5efd9485aba4e3d01942a2cf",name:"Roger Federer"},]}

db.matches.aggregate([{$lookup:{from:"players",let:{ids:{$map:{input:"$players",in:"$$this._id"}}},pipeline:[{$match:{$expr:{$in:["$_id","$$ids"]}}}],as:"players"}}])