多个嵌套数组的 MongoD 大小

Question

我有诗集。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."
                        ]
                    }
                    // ...
                ]
            }
            // ...
        ]
    }
    // ...
]}  

我想计算每首诗的行为和场景数量。我试图做这样的事情，但结果是不正确的。

db.poems.aggregate([{$unwind:"$acts"}, {$unwind:"$acts.scenes"}, {$group: {_id: "$_id", pa: {$push: {poemAct:"$acts"}}, ps: {$push: {poemScenes:"$acts.scenes"}}}}, {$project: {numberOfActs: {$size: "$pa"}, numberOfScenes: {$size: "$ps"}}}]).pretty()

请帮助某人：D

Answer 1

您可以尝试以下聚合。没有$unwind需要在这里。

$map并$size输出具有场景大小$sum的数组并计算数组值。

db.poems.aggregate({
  "$project":{
    "numberOfActs":{"$size":"$acts"},
    "numberOfScenes":{
      "$sum":{
        "$map":{
          "input":"$acts",
          "in":{"$size":"$$this.scenes"}
        }
      }
    }
  }
})