我有一本诗集。集合中的文档具有以下结构:

{
"_id" : "Romeo and Juliet",
"acts" : [ 
    {
        "title" : "ACT I",
        "scenes" : [ 
            {
                "title" : "SCENE I. Verona. A public place.",
                "action" : [ 
                    {
                        "character" : "SAMPSON",
                        "says" : [ 
                            "Gregory, o' my word, we'll not carry coals."
                        ]
                    }, 
                    {
                        "character" : "GREGORY",
                        "says" : [ 
                            "No, for then we should be colliers."
                        ]
                    }, 
                    // ...
                    {
                        "character" : "GREGORY",
                        "says" : [ 
                            "To move is to stir; and to be valiant is to stand:", 
                            "therefore, if thou art moved, thou runn'st away."
                        ]
                    }, 
                    {
                        "character" : "SAMPSON",
                        "says" : [ 
                            "A dog of that house shall move me to stand: I will", 
                            "take the wall of any man or maid of Montague's."
                        ]
                    }, 
                    {
                        "character" : "GREGORY",
                        "says" : [ 
                            "That shows thee a weak slave; for the weakest goes", 
                            "to the wall."
                        ]
                    }, 
                    // ...
            },
            // ...
        ]
    },
    // ...
]}

我需要在 scene 对象中找到对话次数最多的诗(says)。 我尝试使用 $group、$unwind、$sort 等，但结果并不正确。

最佳答案

I need to find the poem with the most number of dialog (says) in the scene object

这可以用以下方式解释。

Count all says across all action in all scenes object for all acts in each poem and show the poem document which has the max says across all poems.

想法是在所有 Action 、所有场景和所有行为中找到最大说，并输出带有最大说的诗歌文档。

嵌套的 $map 和 $max 组合输出不同级别的最大值。

$project 排除删除“maxsaysacrossallacts”字段。

有点像

 db.poems.aggregate([
  {"$addFields":{
    "maxsaysacrossallacts":{
      "$max":{
        "$map":{
          "input":"$acts",
          "as":"maxsaysineachact",
          "in":{
            "$max":{
              "$map":{
                "input":"$$maxsaysineachact.scenes",
                "as":"maxsaysineachscene",
                "in":{
                  "$max":{
                    "$map":{
                      "input":"$$maxsaysineachscene.action",
                      "as":"sayssceneineachaction",
                      "in":{"$size":"$$sayssceneineachaction.says"}
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }},
  {"$sort":{"maxsaysacrossallacts":-1}},
  {"$limit":1},
  {"$project":{"maxsaysacrossallacts":0}}
])

更新:根据下面的评论，如果您需要输出 max says poem 文档，您可以使用下面的聚合查询。

计算所有行为中的所有说，并输出具有最大说数的诗。

db.poems.aggregate([
  {"$addFields":{
    "sumsaysacrossallacts":{
      "$sum":{
        "$map":{
          "input":"$acts",
          "as":"sumsaysineachact",
          "in":{
            "$sum":{
              "$map":{
                "input":"$$sumsaysineachact.scenes",
                "as":"sumsaysineachscene",
                "in":{
                  "$sum":{
                    "$map":{
                      "input":"$$sumsaysineachscene.action",
                      "as":"sayssceneineachaction",
                      "in":{"$size":"$$sayssceneineachaction.says"}
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }},
  {"$sort":{"sumsaysacrossallacts":-1}},
  {"$limit":1},
  {"$project":{"sumsaysacrossallacts":0}}
])

关于arrays - MongoDB 计算最常见的嵌套数组，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/48731111/