Aves

.aggregate([
  {$unwind: '$demands'},
  {$group: {
    _id: null,
    placementIdList: {$addToSet: '$demands.placementId'}
  }}
])

.aggregate([
  {$unwind: "$params"},
  {$match: {"params.one": true}},
  {$project: {
    _id: 0,
    name: 1,
    age: 1,
    two: "$params.two",
    three: "$params.three"}
  }
])