mongodb - 仅在 MongoDB 中满足特定条件时分组

Question

如果组事件的数量超过 3，我想通过它们的 pid(仅组)对一些特定记录进行分组。

示例:

此处group (pid: 200)的事件数为4，必须分组。

- Events -
----------
{_id: ObjectId, type: 'private', pid: 140, data: {...}},
{_id: ObjectId, type: 'group', pid: 800, data: {...}}, // << group 800
{_id: ObjectId, type: 'group', pid: 200, data: {...}}, // << group 200
{_id: ObjectId, type: 'group', pid: 200, data: {...}}, // << group 200
{_id: ObjectId, type: 'private', pid: 140, data: {...}},
{_id: ObjectId, type: 'group', pid: 200, data: {...}}, // << group 200
{_id: ObjectId, type: 'group', pid: 200, data: {...}}, // << group 200
{_id: ObjectId, type: 'private', pid: 130, data: {...}},

此处对group (pid: 200)进行了分组，并将is_too_long: true添加到记录中。并且 group (pid: 800) 没有按预期分组。

- Results -
-----------
{_id: ObjectId, type: 'private', pid: 140, data: {...}},
{_id: ObjectId, type: 'group', pid: 800, data: {...}, is_too_long: false}, // << group 800
{_id: ObjectId, type: 'private', pid: 140, data: {...}},
{_id: ObjectId, type: 'group', pid: 200, is_too_long: true}}, // << group 200 (with [is_too_long: true])
{_id: ObjectId, type: 'private', pid: 130, data: {...}, is_too_long: false},

我尝试了其他一些查询，但都没有用!请帮助我!

Answer 1

• $facet 分隔private 和group 文档，
• $group 按 pid 和数组中的文档分组
• $cond 检查条件，如果分组文档大于或等于 3，则从数组中切出单个元素并设置 is_too_long: true 否则为 false
• $map 迭代 docs 数组的循环并放入 bool 属性 is_too_long
• $unwind 解构root数组
• $replaceRoot 将 root 对象替换为 root
• $concatArrays，连接private和group数组
• $unwind 解构root数组
• $replaceRoot 替换根中的root对象

db.collection.aggregate([
  {
    $facet: {
      private: [{ $match: { type: "private" } }],
      group: [
        { $match: { type: "group" } },
        {
          $group: {
            _id: "$pid",
            root: { $push: "$$ROOT" }
          }
        },
        {
          $project: {
            root: {
              $cond: [
                { $gte: [{ $size: "$root" }, 3] },
                {
                  is_too_long: true,
                  docs: { $slice: ["$root", 1] }
                },
                {
                  is_too_long: false,
                  docs: "$root"
                }
              ]
            }
          }
        },
        {
          $project: {
            root: {
              $map: {
                input: "$root.docs",
                in: { $mergeObjects: ["$$this", { is_too_long: "$root.is_too_long" }] }
              }
            }
          }
        },
        { $unwind: "$root" },
        { $replaceRoot: { newRoot: "$root" } }
      ]
    }
  },
  { $project: { root: { $concatArrays: ["$private", "$group"] } } },
  { $unwind: "$root" },
  { $replaceRoot: { newRoot: "$root" } }
])

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