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db.collection.aggregate([{$match:{_id:1}},{$project:{responses:{$reduce:{input:"$forms",initialValue:[],in:{$concatArrays:[{$reduce:{input:"$$this.history",initialValue:[],in:{$concatArrays:["$$value","$$this.responses"]}}},"$$value"]}}}}},{$project:{responses:{$filter:{input:"$responses",as:"item",cond:{$eq:["$$item.client_id",1]}}}}}])