Mongodb 如何从以前的$group中提取多个$bucket集合

我想在$bucket函数中单独处理$group的结果

我的数据：

{ "_id" : 1, "title" : "The Pillars of Society", "artist" : "Grosz", "year" : 1926, "type": 1}
{ "_id" : 2, "title" : "Melancholy III", "artist" : "Munch", "year" : 1902, "type": 1}
{ "_id" : 3, "title" : "Dancer", "artist" : "Miro", "year" : 1925, "type": 1}
{ "_id" : 4, "title" : "The Great Wave off Kanagawa", "artist" : "Hokusai", "type": 1}
{ "_id" : 5, "title" : "The Persistence of Memory", "artist" : "Dali", "year" : 1931, "type": 3}
{ "_id" : 6, "title" : "Composition VII", "artist" : "Kandinsky", "year" : 1913, "type": 3}
{ "_id" : 7, "title" : "The Scream", "artist" : "Munch", "year" : 1893, "type": 2}
{ "_id" : 8, "title" : "Blue Flower", "artist" : "O'Keefe", "year" : 1918, "type": 2}

我需要做的是：

按类型分组->返回3组

按年份范围划分，每组在1年内返回

获取2中每个桶的统计信息，1中每个组的统计信息

我希望在一个查询中处理所有内容，而无需多次运行“匹配”以按类型筛选

预期产出：

{
    "1": {
        1900: [{ "_id" : 2, "title" : "Melancholy III", "artist" : "Munch", "year" : 1902, "type": 1}],
        1925: [{ "_id" : 1, "title" : "The Pillars of Society", "artist" : "Grosz", "year" : 1926, "type": 1}, { "_id" : 3, "title" : "Dancer", "artist" : "Miro", "year" : 1925, "type": 1}],
        "other": [{ "_id" : 4, "title" : "The Great Wave off Kanagawa", "artist" : "Hokusai", "type": 1}]
    }
    "2": {
        1900: [{ "_id" : 8, "title" : "Blue Flower", "artist" : "O'Keefe", "year" : 1918, "type": 2}],
        1925: [],
        "other": [{ "_id" : 7, "title" : "The Scream", "artist" : "Munch", "year" : 1893, "type": 2}]
    },
    "3": {
        1900: [{ "_id" : 6, "title" : "Composition VII", "artist" : "Kandinsky", "year" : 1913, "type": 3}],
        1925: [{ "_id" : 5, "title" : "The Persistence of Memory", "artist" : "Dali", "year" : 1931, "type": 3}],
        "other": []
    }
}

---

我知道如何执行一个bucket、一个组和一个match，但我不知道如何在不重复match查询的情况下将其组合到同一聚合管道中以获得预期结果（例如，使用$facet是可能的）。

使用此管道可以实现类似的输出：

db.artwork.aggregate([
    { $bucket: {
        groupBy: "$year",
        boundaries: [1900, 1925, 1950],
        default: "Other",
        output: { titles: { $push: "$$ROOT" }}
    }},
    { $unwind: "$titles" },
    { $group: {
        _id: { type: "$titles.type", year: "$_id" },
        titles: { $push: "$titles" }
    }},
    { $project: {
        _id: 0,
        type: "$_id.type",
        year: "$_id.year",
        titles: 1
    }},
    { $group: {
        _id: { type: "$type" },
        buckets: { $push: "$$ROOT" }
    }},
    { $project: {
        _id: 0,
        type: "$_id.type",
        buckets: { year: 1, titles: 1 }
    }}
])

其中：

{
    "type" : 1,
    "buckets" : [
        {
            "year" : 1900,
            "titles" : [ { "_id" : 2, "title" : "Melancholy III", "artist" : "Munch", "year" : 1902, "type" : 1 } ]
        },
        {
            "year" : 1925,
            "titles" : [
                { "_id" : 1, "title" : "The Pillars of Society", "artist" : "Grosz", "year" : 1926, "type" : 1 },
                { "_id" : 3, "title" : "Dancer", "artist" : "Miro", "year" : 1925, "type" : 1}
            ]
        },
        {
            "year" : "Other",
            "titles" : [ { "_id" : 4, "title" : "The Great Wave off Kanagawa", "artist" : "Hokusai", "type" : 1 } ]
        }
    ]
},

{
    "type" : 2,
    "buckets" : [
        {
            "year" : 1900,
            "titles" : [ { "_id" : 8, "title" : "Blue Flower", "artist" : "O'Keefe", "year" : 1918, "type" : 2 } ]
        },
        {
            "year" : "Other",
            "titles" : [ { "_id" : 7, "title" : "The Scream", "artist" : "Munch", "year" : 1893, "type" : 2 } ]
        }
    ]
},

{
    "type" : 3,
    "buckets" : [
        {
            "year" : 1900,
            "titles" : [ { "_id" : 6, "title" : "Composition VII", "artist" : "Kandinsky", "year" : 1913, "type" : 3 } ]
        },
        {
            "year" : 1925,
            "titles" : [ { "_id" : 5, "title" : "The Persistence of Memory", "artist" : "Dali", "year" : 1931, "type" : 3 } ]
        }
    ]
}

项目阶段主要是格式化数据，但这里重要的是首先获取所有用于分组项目的数据（每次失误的分类是我们还没有的唯一输出），用$unwind分隔每个项目，并使用$group阶段嵌套阵列

您想要的输出可以通过$cond操作符实现，但它不是动态的，因为您必须显式地写入字段。更多关于这方面的信息可以在这篇文章中找到