如果在MongoDB中只满足特定条件的话

Question

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

示例：

这里，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: {...}},

在这里，group (pid: 200)被分组，is_too_long: true被添加到记录中。并且group (pid: 800)没有按预期进行分组。

- 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},

我尝试了一些其他的查询，但都没有用！请帮帮我!

Answer 1

• $facet来分离private和group文档，
• 数组中的$group由pid和group文档组成
• 如果分组文档大于或等于3，则从数组中分割单个元素，并设置$cond，否则为false
• $map迭代docs数组的循环并放置布尔属性is_too_long
• $unwind解构root阵列
• $replaceRoot将root对象替换为根
• $concatArrays、concat private和group数组
• $unwind解构root阵列
• $replaceRoot替换根目录中的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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