从线性mongo集合创建4级嵌套对象聚合输出

Question

我有以下模式

{
        question: String,
        answer: Number,
        option1: String,
        option2: String,
        option3: String,
        option4: String,
        subject: String,
        chapter: String,
        topic: String,
        subtopic: String,
        tags: { type: Array, default: [] },
        difficulty: String,
        media: { type: String, default: "" }
}

我想从这个问题模式创建一个索引，其中索引中的唯一条目可以通过元组(主题、章节、主题、子主题)来标识。

{
    "subject": {
        "chapter": {
            "topic": ["subtopics"],
            "topic": ["subtopics"],
        },
        "chapter": {
            "topic": ["subtopics"],
            "topic": ["subtopics"],
        },
    },
    "subject": {
        "chapter": {
            "topic": ["subtopics"],
            "topic": ["subtopics"],
        },
        "chapter": {
            "topic": ["subtopics"],
            "topic": ["subtopics"],
        },
    },
}

为了达到上面的结果，我一直在尝试一些聚合，到目前为止我已经能够达到目的了。

{
    "subject": ["chapters"],
    "subject": ["chapters"],
    "subject": ["chapters"],
    "subject": ["chapters"],
}

跟随管道在猫鼬中的应用

            {
                $group: {
                    _id: "$subject",
                    chapters: { $push: "$chapter" }
                }
            },
            {
                $group: {
                    _id: null,
                    chapters: { $push: { "k": "$_id", "v": "$chapters" } }
                }
            },
            {
                $replaceRoot: { "newRoot": { "$arrayToObject": "$chapters" } }
            }

当我试图扩展上述逻辑以包含主题和子主题时，使用

            {
                $group: {
                    _id: "$subject",
                    chapters: { $push: { "k": "$chapter", "v": { topic: "$topic", subtopic: "$subtopic" } } }
                }
            },
            {
                $group: {
                    _id: null,
                    chapters: { $push: { "k": "$_id", "v": { "$arrayToObject": "$chapters" } } }
                }
            },
            {
                $replaceRoot: { "newRoot": { "$arrayToObject": "$chapters" } }
            }

我得到以下输出

{
    "subject": {
        "chapter": {
            "topic": "value",
            "subtopic": "value"
        },
        "chapter": {
            "topic": "value",
            "subtopic": "value"
        },
    },
    "subject": {
        "chapter": {
            "topic": "value",
            "subtopic": "value"
        },
        "chapter": {
            "topic": "value",
            "subtopic": "value"
        },
    },
}

​

​

问题是，章节是最后一个主题和子主题的对象，只有，我知道我在哪里犯了错误，但我不知道如何解决它。

Answer 1

您可以使用这种主要利用$objectToArray的聚合，但是数据重组并不那么优雅：

db.collection.aggregate(
    [
        { 
            "$group" : { 
                "_id" : { 
                    "subject" : "$subject", 
                    "chapter" : "$chapter", 
                    "topic" : "$topic"
                }, 
                "topics" : { 
                    "$push" : "$subtopic"
                }
            }
        }, 
        { 
            "$addFields" : { 
                "topic" : { 
                    "k" : "$_id.topic", 
                    "v" : "$topics"
                }
            }
        }, 
        { 
            "$group" : { 
                "_id" : { 
                    "subject" : "$_id.subject", 
                    "chapter" : "$_id.chapter"
                }, 
                "topics" : { 
                    "$push" : "$topic"
                }
            }
        }, 
        { 
            "$addFields" : { 
                "topics" : { 
                    "$arrayToObject" : "$topics"
                }
            }
        }, 
        { 
            "$addFields" : { 
                "chapters" : [
                    { 
                        "k" : "$_id.chapter", 
                        "v" : "$topics"
                    }
                ]
            }
        }, 
        { 
            "$addFields" : { 
                "chapters" : { 
                    "$arrayToObject" : "$chapters"
                }
            }
        }, 
        { 
            "$group" : { 
                "_id" : null, 
                "subject" : { 
                    "$push" : { 
                        "k" : "$_id.subject", 
                        "v" : "$chapters"
                    }
                }
            }
        }, 
        { 
            "$project" : { 
                "final" : { 
                    "$arrayToObject" : "$subject"
                }
            }
        }, 
        { 
            "$replaceRoot" : { 
                "newRoot" : "$final"
            }
        }
    ]);