mongodb - mongo 将单个对象转换为一个元素数组

Question

我有以下问题。在这个示例数据集中:

https://mongoplayground.net/p/itNnrDzZ4JQ

[
  {
    "name": "test",
    "questions": [
      {
        "headline": "headline 1",
        "answer": {
          "@id": "001",
          "m_IMG": {
            "type": "06",
            "img": {
              "@id": "1111",
              "shape": [
                {
                  "@src": "/1_1.jpg",
                  "@type": "Z05"
                },
                {
                  "@src": "/1_2.jpg",
                  "@type": "Z08"
                }
              ]
            }
          },
          "text": "text1"
        }
      },
      {
        "headline": "Headline 2",
        "answer": [
          {
            "@id": "001",
            "m_IMG": {
              "@type": "24",
              "img": {
                "@id": "1111",
                "shape": {
                  "@src": "/2_1.jpg",
                  "@type": "Z05"
                }
              },
              "text": "Test2"
            }
          },
          {
            "@id": "002",
            "m_IMG": {
              "@typeName": "",
              "@type": "25",
              "img": {
                "@id": "2222",
                "shape": [
                  {
                    "@src": "/2_1.jpg",
                    "@type": "Z05"
                  },
                  {
                    "@src": "2_2.jpg",
                    "@type": "Z08"
                  }
                ]
              }
            },
            "text": "Test3"
          }
        ]
      }
    ]
  }
]

您会发现，如果一个问题只有一个答案，则它会被表示为一个对象。如果存在多个，则它是一个数组。 shape 节点也是如此。我想知道将这些节点转换为始终数组的最佳方法是什么(因此，如果存在一个答案，它将是一个元素的数组)。

Answer 1

• $map 迭代 questions 数组的循环
• 检查条件，如果答案不是数组，然后将其放入数组括号中，并作为$map输入，以迭代answer数组的循环
• 检查条件是否不是shape数组十将其包裹到数组括号中
• $mergeObjects 带有子文档 img, m_IMG 对象
• $mergeObjects 包含当前文档和更新的 answer 数组

db.collection.aggregate([
  {
    $set: {
      questions: {
        $map: {
          input: "$questions",
          as: "q",
          in: {
            $mergeObjects: [
              "$$q",
              {
                answer: {
                  $map: {
                    input: {
                      $cond: [
                        { $eq: [{ $isArray: "$$q.answer" }, true] },
                        "$$q.answer",
                        ["$$q.answer"]
                      ]
                    },
                    as: "a",
                    in: {
                      $mergeObjects: [
                        "$$a",
                        {
                          m_IMG: {
                            $mergeObjects: [
                              "$$a.m_IMG",
                              {
                                img: {
                                  $mergeObjects: [
                                    "$$a.m_IMG.img",
                                    {
                                      shape: {
                                        $cond: [
                                          { $eq: [{ $isArray: "$$a.m_IMG.img.shape" }, true] },
                                          "$$a.m_IMG.img.shape",
                                          ["$$a.m_IMG.img.shape"]
                                        ]
                                      }
                                    }
                                  ]
                                }
                              }
                            ]
                          }
                        }
                      ]
                    }
                  }
                }
              }
            ]
          }
        }
      }
    }
  }
])

Playground