在单个聚合中多次查找后合并 Mongo 个文档

Question

我无法尝试合并我的文档结果。这是我的查询和数据

{"_id":"5c21ab13d03013b384f0de26",
"roles":["5c21ab31d497a61195ce224c","5c21ab4ad497a6f348ce224d","5c21ab5cd497a644b6ce224e"],
"agency":"5b4ab7afd6ca361cb38d6a60","agents":["5b4ab5e897b24f1c4c8e3de3"]}

这里是查询

  return db.collection('projects').aggregate([
  {
    $match: {
      agents: ObjectId(agent)
    }
  },
  {
    $unwind: "$agents"
  },
  {
    $lookup: {
      from: "agents",
      localField: "agents",
      foreignField: "_id",
      as: "agents"
    }
  },
  {
    $unwind: {
      path: "$roles",
      preserveNullAndEmptyArrays: true
    }
  },
  {
    $lookup: {
      from: "roles",
      localField: "roles",
      foreignField: "_id",
      as: "roles"
    }
  },
  {
    $lookup: {
      from: "agencies",
      localField: "agency",
      foreignField: "_id",
      as: "agency"
    }
  }
])

如您所见，项目集合中的一个条目有两个数组，在对每个条目执行查找之前展开，然后对 "agency" 字段执行最终查找。

但是，当我从该查询中获得结果时，我得到的文档数等于角色数。例如，我正在聚合的项目有 3 个角色和 1 个代理。因此，我返回了一个包含 3 个对象的数组，每个对象对应一个对象，而不是包含所有三个角色的角色数组的单个文档。代理数组也有可能有多个值。

迷路了...

Answer 1

您不必在 $lookup 之前运行 $unwind。 localField 部分指出：

If your localField is an array, you may want to add an $unwind stage to your pipeline. Otherwise, the equality condition between the localField and foreignField is foreignField: { $in: [ localField.elem1, localField.elem2, ... ] }

所以基本上如果你不运行 $unwind 例如 roles 那么你将得到一个 roles 的数组作为 ObjectIds 替换为第二个集合中的对象数组。

因此您可以尝试以下聚合：

db.collection('projects').aggregate([
    {
        $match: {
            agents: ObjectId(agent)
        }
    },
    {
        $lookup: {
            from: "agents",
            localField: "agents",
            foreignField: "_id",
            as: "agents"
        }
    },
    {
        $lookup: {
            from: "roles",
            localField: "roles",
            foreignField: "_id",
            as: "roles"
        }
    },
    {
        $lookup: {
            from: "agencies",
            localField: "agency",
            foreignField: "_id",
            as: "agency"
        }
    }
])

在单个聚合中多次查找后合并 Mongo 个文档

Combine Mongo Documents after multiple lookups in single aggregation

arrays

aggregation

mongodb