MongoDB合并按键更新值的对象数组

一个复杂的查询.

1. $map -迭代$$new.analytics数组中的每个元素.

1.1 $cond-判断迭代元素的type是否存在于现有的analytics数组中.如果是，则转到第1.1.1节.否则，返回newItem对象.

1.1.1.$first-从结果1.1.1.1返回第一个文档.

1.1.1.1.$map-迭代现有analytics数组的匹配元素，返回该元素，并通过添加新的value来覆盖现有的value.

  {
    $merge: {
      into: "analytics",
      on: [
        "key"
      ],
      whenMatched: [
        {
          $replaceWith: {
            key: "$key",
            analytics: {
              $map: {
                input: "$$new.analytics",
                as: "newItem",
                in: {
                  $cond: [
                    {
                      $in: [
                        "$$newItem.type",
                        "$analytics.type"
                      ]
                    },
                    {
                      $first: {
                        $map: {
                          input: {
                            $filter: {
                              input: "$analytics",
                              cond: {
                                $eq: [
                                  "$$this.type",
                                  "$$newItem.type"
                                ]
                              }
                            }
                          },
                          as: "oldItem",
                          in: {
                            $mergeObjects: [
                              "$$newItem",
                              {
                                value: {
                                  $sum: [
                                    "$$oldItem.value",
                                    "$$newItem.value"
                                  ]
                                }
                              }
                            ]
                          }
                        }
                      }
                    },
                    "$$newItem"
                  ]
                }
              }
            }
          }
        }
      ],
      whenNotMatched: "insert"
    }
  }

此外，这是支持$let运算符的另一个版本:

{
    $merge: {
      into: "analytics",
      on: ["key"],
      whenMatched: [
        {
          $replaceWith: {
            key: "$key",
            analytics: {
              $map: {
                input: "$$new.analytics",
                as: "newItem",
                in: {
                  $cond: [
                    {
                      $in: [
                        "$$newItem.type",
                        "$analytics.type"
                      ],
                    },
                    {
                      $let: {
                        vars: {
                          oldItem: {
                            $first: {
                              $filter: {
                                input:
                                  "$analytics"
                                cond: {
                                  $eq: [
                                    "$$this.type",
                                    "$$newItem.type"
                                  ]
                                }
                              }
                            }
                          }
                        },
                        in: {
                          $mergeObjects: [
                            "$$newItem",
                            {
                              value: {
                                $sum: [
                                  "$$oldItem.value",
                                  "$$newItem.value"
                                ]
                              }
                            }
                          ]
                        }
                      }
                    },
                    "$$newItem"
                  ]
                }
              }
            }
          }
        }
      ],
      whenNotMatched: "insert"
    }
  }