[{persons:[{personId:"61cd90594947be000838f7c1",name:"John Doe",employment:[{employmentId:"61cd9059494abe000838f7c8",type:"Full time",salary:1010101}]},{personId:"61cd90594947be000838f7c2",name:"Jane Austin",employment:[{employmentId:"61cd9059494abe000838f7c8",type:"Part time",salary:11011111}]}]},]

db.collection.update({},[{$set:{persons:{$map:{input:"$persons",as:"person",in:{$cond:[{$eq:["61cd90594947be000838f7c1","$$person.personId"]},{$mergeObjects:["$$person",{employment:{$cond:[{$in:["61cd9059494abe000838f7c8","$$person.employment.employmentId"]},{$map:{input:"$$person.employment",as:"employment",in:{$cond:[{$eq:["61cd9059494abe000838f7c8","$$employment.employmentId"]},{$mergeObjects:["$$employment",{employmentId:"61cd9059494abe000838f7c8",frequency:"weekly"}]},"$$employment"]}}},{$concatArrays:["$$person.employment",[{personId:"61cd90594947be000838f7c1",employmentId:"61cd9059494abe000838f7c8",frequency:"weekly"}]]}]},}]},"$$person"]}}}}}])