MongoDB聚合：在不加入的情况下计算查找的结果

Question

我正在处理此查询：

    customers.aggregate: [
  {$lookup: {
    from: "users",
    localField: "_id",
    foreignField: "customerId",
    as: "users"
  }}, 
  {$lookup: {
    from: "templates",
        let: {localField: "$_id"},
    pipeline: [{
    $match: { $and: [{
      $expr: { $eq: ["$customerId", "$$localField"]}},
        {module: false}]
    }}],
    as: "templates"
  }},
  {$lookup: {
    from: "publications",
    localField: "_id",
    foreignField: "customerId",
    as: "publications"
  }},
 {$lookup: {
    from: "documents",
    let: {localField: "$_id"},
    pipeline: [{
    $match: { $and: [{
      $expr: { $eq: ["$customerId", "$$localField"]}},
        {createdAt: {$gte: {$date: "<someDate>"}}}]
    }}],
    as: "recentDocuments"
  }}
]

在最后一个查找阶段，我是根据customerId根据_id字段字段来过滤文档的，而不是＆lt; lyt＆gt ;然后将这些文档加入到各个“客户”对象。 在此步骤之后，或者即使在同一步骤中，我也想在每个结果的“客户”文档中添加一个新字段，并使用“文档”中的所有文档数量（不仅是传递时间过滤器的文档）数量“用customerId字段值收集，与客户文档的_id相对应。而且我也希望不将这些文档加入客户对象，因为我只需要各自customerId的文档总数。我只能使用扩展JSON V1严格模式语法。 结果看起来像：

customers: [
 0: {
  users: [...],
  templates: [...],
  publications: [...],
  recentDocuments: [...],
  totalDocuments: <theCountedNumber>
 },
 1: {...},
 2: {...},
 ...
] 

Answer 1

使用 $set 和 $size

db.customers.aggregate([
  {
    $lookup: {
      from: "documents",
      let: { localField: "$_id" },
      pipeline: [
        {
          $match: {
            $and: [
              { $expr: { $eq: [ "$customerId", "$localField" ] } }
            ]
          }
        }
      ],
      as: "recentDocuments"
    }
  },
  {
    $set: {
      totalDocuments: { $size: "$recentDocuments" }
    }
  }
])

mongoplayground

Answer 2

所以周四我找到了解决我的问题的正确语法。它是这样的：

db.customers.aggregate([
    {
    $lookup: {
    from: "users",
    localField: "_id",
    foreignField: "customerId",
    as: "users"
  }}, 
  {$lookup: {
    from: "templates",
        let: {localField: "$_id"},
    pipeline: [{
    $match: { $and: [{
      $expr: { $eq: ["$customerId", "$localField"]}},
        {module: false}]
    }}],
    as: "templates"
  }},
  {$lookup: {
    from: "publications",
    localField: "_id",
    foreignField: "customerId",
    as: "publications"
  }},
  {$lookup: {
    from: "documents",
    let: {localField: "$_id"},
    pipeline: [{
    $match: { $and: [{
      $expr: { $eq: ["$customerId", "$localField"]}},
        {createdAt: {$gte: {$date: "<someDate>"}}}]
    }}],
    as: "recentDocuments"
  },
  {$lookup: {
    from: "documents",
    let: {localField: "$_id"},
    pipeline: [{
    $match: {$and: [{
      $expr: {$eq: ["$customerId", "$localField"]}},
      { $count: "count" }],
    as: "documentsNumber"
  }}
])

此命令将在聚合管道的最后阶段再次检查文档集合，但这一次将返回所有文档而不是按时间段进行过滤，然后将结果对象交换为每个“ customer”对象，其数组中的一项是所有文档的数量。该数组稍后可以使用 $unwind 操作“展开”，但事实证明它会大大降低性能，因此 - 被省略。我真的希望这能帮助有人解决类似的问题。