在$week mongodb查询中没有匹配周记录时，如何显示0表示周

db.collection.aggregate([
  {
    $match: {
      week: { $eq: "某一周" }
    }
  }
])

db.collection.aggregate([
  {
    $match: {
      week: { $eq: "某一周" }
    }
  },
  {
    $group: {
      _id: null,
      count: { $sum: 1 }
    }
  }
])

db.collection.aggregate([
  {
    $match: {
      week: { $eq: "某一周" }
    }
  },
  {
    $group: {
      _id: null,
      count: { $sum: 1 }
    }
  },
  {
    $project: {
      count: {
        $cond: {
          if: { $gt: ["$count", 0] },
          then: "$count",
          else: 0
        }
      }
    }
  }
])