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db.collection.aggregate([{$project:{"map.cities":{$let:{vars:{faction:{"$getField":{"input":{$first:{$filter:{input:"$players",cond:{$eq:["$$this.userid","64d3ebfb42fb5b118b928f5c"]}}}},"field":"faction"}}},in:{$map:{input:"$map.cities",in:{$mergeObjects:[{name:"$$this.name","x":"$$this.x","y":"$$this.y","owner":"$$this.owner"},{$cond:[{$eq:["$$this.owner","$$faction"]},"$$this",{}]}]}}}}}}}])