[{name:"company 1",createPurchaseOrder:[{partyName:"p1",poNumber:"789",},{partyName:"p2",poNumber:"700",},{partyName:"p3",poNumber:"889",},{partyName:"p1",poNumber:"800",},{partyName:"p1",poNumber:"200",},]}]

db.collection.aggregate([{$match:{name:"company 1"}},{$addFields:{createPurchaseOrder:{$filter:{input:{$ifNull:["$createPurchaseOrder",[]]},cond:{$eq:["$$this.partyName","p1"]}}}}},{$unwind:"$createPurchaseOrder"},{$replaceRoot:{newRoot:"$createPurchaseOrder"}}])