这个问题源于展开后的查找，它像carryout连接一样增加了文档的数量。
例如，假设我们有这个文档：

{a: [1,2,3], b: ['x', 'y', 'z']}

字符串
解压缩a后，我们得到

{ a: 1, b: ['x',  'y', 'z']}
{ a: 2, b: ['x',  'y', 'z']}
{ a: 3, b: ['x',  'y', 'z']}

型
然后展开b，我们得到

{ a: 1, b: 'x'}
{ a: 1, b: 'y'}
{ a: 1, b: 'z'}
{ a: 2, b: 'x'}
{ a: 2, b: 'y'}
{ a: 2, b: 'z'}
{ a: 3, b: 'x'}
{ a: 3, b: 'y'}
{ a: 3, b: 'z'}

型
你可以在任何解卷发生之前perform the lookups and zip the looked up fields来解决这个问题。

await entityModel
  .aggregate([{
      $match: {
        _id: new mongoose.Types.ObjectId(req.query._id)
      }
    },
    {
      $lookup: {
        from: "invoices",
        localField: "_id",
        foreignField: "customer",
        as: "invoices",
        pipeline: [{
            $lookup: {
              from: "accounts",
              localField: "account",
              foreignField: "_id",
              pipeline: [{
                $project: {
                  _id: 1,
                  name: 1
                }
              }],
              as: "account"
            }
          },
          {
            $unwind: "$account"
          },
          { // adds a field to mark the collection we looked up from
            "$addFields": {
              "kind": "invoice"
            }
          }
        ]
      }
    },
    {
      $lookup: {
        from: "prs",
        localField: "_id",
        foreignField: "customer",
        as: "prs",
        pipeline: [{
            $lookup: {
              from: "accounts",
              localField: "account",
              foreignField: "_id",
              pipeline: [{
                $project: {
                  _id: 1,
                  name: 1
                }
              }],
              as: "account"
            }
          },
          {
            $unwind: "$account"
          },
          { // adds a field to mark the collection we lookedup from
            "$addFields": {
              "kind": "pr"
            }
          }
        ]
      }
    },
    {
      $project: {
        _id: 1,
        name: 1,
        type: 1,
        docs: {
          $zip: {
            inputs: [
              "$prs",
              "$invoices"
            ],
            useLongestLength: true
          }
        }
      }
    },
    {
      $unwind: "$docs"
    },
    {
      $unwind: "$docs"
    },
    { // We exclude missing document because we set the `useLongestLength` option when zipping invoices and prs.
      $match: {
        docs: {
          $ne: null
        }
      }
    },
    { // The layout of the results are document wise. It should be possible to layout differently.
      $group: {
        _id: {
          status: "$docs.status",
          account: "$docs.account._id",
          kind: "$docs.kind",
          year: {
            $year: "$docs.created_at"
          }
        },
        sum_usd: {
          $sum: "$docs.total_usd"
        },
        sum_iqd: {
          $sum: "$docs.total_iqd"
        }
      }
    }
  ])

型
您可以通过将组阶段更改为以下方式更改the layout of the results：

await entityModel
  .aggregate([{
      $match: {
        _id: new mongoose.Types.ObjectId(req.query._id)
      }
    },
    {
      $lookup: {
        from: "invoices",
        localField: "_id",
        foreignField: "customer",
        as: "invoices",
        pipeline: [{
            $lookup: {
              from: "accounts",
              localField: "account",
              foreignField: "_id",
              pipeline: [{
                $project: {
                  _id: 1,
                  name: 1
                }
              }],
              as: "account"
            }
          },
          {
            $unwind: "$account"
          },
          {
            "$addFields": {
              "kind": "invoice"
            }
          }
        ]
      }
    },
    {
      $lookup: {
        from: "prs",
        localField: "_id",
        foreignField: "customer",
        as: "prs",
        pipeline: [{
            $lookup: {
              from: "accounts",
              localField: "account",
              foreignField: "_id",
              pipeline: [{
                $project: {
                  _id: 1,
                  name: 1
                }
              }],
              as: "account"
            }
          },
          {
            $unwind: "$account"
          },
          {
            "$addFields": {
              "kind": "pr"
            }
          }
        ]
      }
    },
    {
      $project: {
        _id: 1,
        name: 1,
        type: 1,
        docs: {
          $zip: {
            inputs: [
              "$prs",
              "$invoices"
            ],
            useLongestLength: true
          }
        }
      }
    },
    {
      $unwind: "$docs"
    },
    {
      $unwind: "$docs"
    },
    {
      $match: {
        docs: {
          $ne: null
        }
      }
    },
    {
      $group: {
        _id: {
          status: "$docs.status",
          account: "$docs.account._id",
          year: {
            $year: "$docs.created_at"
          }
        },
        pr_sum_usd: {
          $sum: {
            $cond: [{
                $eq: [
                  "$docs.kind",
                  "pr"
                ]
              },
              "$docs.total_usd",
              0
            ]
          }
        },
        pr_sum_iqd: {
          $sum: {
            $cond: [{
                $eq: [
                  "$docs.kind",
                  "pr"
                ]
              },
              "$docs.total_iqd",
              0
            ]
          }
        },
        inv_sum_usd: {
          $sum: {
            $cond: [{
                $eq: [
                  "$docs.kind",
                  "invoice"
                ]
              },
              "$docs.total_usd",
              0
            ]
          }
        },
        inv_sum_iqd: {
          $sum: {
            $cond: [{
                $eq: [
                  "$docs.kind",
                  "invoice"
                ]
              },
              "$docs.total_iqd",
              0
            ]
          }
        }
      }
    }
  ])

型