如何在 mongodb 聚合中展开嵌套的 object arrays？

Question

我有一些包含另一个数组的对象数组的数据。 我正在尝试展开课程数组，然后展开需求数组以匹配主题，然后将所有内容组合在一起。

到目前为止，我可以很好地使用课程数组。 但我就是无法为第二个数组要求做同样的事情。

[
  {
    "_id": 1,
    "name": "provider name",
    "courses": [
      {
        "_id": 1,
        "name": "course name",
        "requirements": [
          {
            "subjects": [
              "SubjectA::B",
              "SubjectB::B",
              "SubjectC::B"
            ]
          },
          {
            "subjects": [
              "SubjectA::B",
              "SubjectB::B",
              "SubjectC::B"
            ]
          }
        ]
      }
    ]
  }
]

首先我解开 arrays

  {
    $unwind: {
      path: '$courses',
      preserveNullAndEmptyArrays: true
    }
  },
  {
    $unwind: {
      path: '$courses.requirements',
      preserveNullAndEmptyArrays: true
    }
  },

我如何对第一个数组进行分组

  {
    $group: {
      _id: '$_id',
      root: { $mergeObjects: '$$ROOT' },
      courses: { $push: '$courses' }
    }
  },
  {
    $replaceWith: {
      $mergeObjects: ['$root', '$$ROOT'],
    }
  },
  {
    $project: { root: 0 }
  },

预计 Output

[
  {
    "_id": 1,
    "name": "provider name",
    "courses": [
      {
        "_id": 1,
        "name": "course name",
        "requirements": [
          {
            "subjects": [
              "SubjectA::B",
              "SubjectB::B",
              "SubjectC::B"
            ]
          },
          {
            "subjects": [
              "SubjectA::B",
              "SubjectB::B",
              "SubjectC::B"
            ]
          }
        ]
      }
    ]
  }
]

但我明白了

[
  {
    "_id": 1,
    "name": "provider name",
    "courses": [
      {
        "_id": 1,
        "name": "course name",
        "requirements": [
          {
            "subjects": [
              "SubjectA::B",
              "SubjectB::B",
              "SubjectC::B"
            ]
          },
          {
            "subjects": [
              "SubjectA::B",
              "SubjectB::B",
              "SubjectC::B"
            ]
          }
        ]
      },
      {
        "_id": 1,
        "name": "course name",
        "requirements": [
          {
            "subjects": [
              "SubjectA::B",
              "SubjectB::B",
              "SubjectC::B"
            ]
          },
          {
            "subjects": [
              "SubjectA::B",
              "SubjectB::B",
              "SubjectC::B"
            ]
          }
        ]
      }
    ]
  }
]

Answer 1

您可以通过以下阶段重建游览 arrays，

• $group by _id和courses._id得到name和课程名字，并构造requirements数组
• $group by only _id并获取name并重建courses数组

  {
    $group: {
      _id: {
        _id: "$_id",
        cId: "$courses._id"
      },
      name: { $first: "$name" },
      course_name: { $first: "$courses.name" },
      requirements: { $push: "$courses.requirements" }
    }
  },
  {
    $group: {
      _id: "$_id._id",
      name: { $first: "$name" },
      courses: {
        $push: {
          _id: "$_id.cId",
          name: "$course_name",
          requirements: "$requirements"
        }
      }
    }
  }

操场