MongoDb Pipeline Aggregation $unwind 子子文档答案

【问题标题】：MongoDb Pipeline Aggregation $unwind sub sub documentsMongoDb Pipeline Aggregation $unwind 子子文档
【发布时间】：2015-05-13 13:49:56
【问题描述】：

我正在尝试使用 MongoDb 列出展开嵌套数组。

一个产品包含任务，每个任务可以有零个、一个或多个子任务。

这是一个示例产品文档：

db.products.find({_id: ObjectId("554a13d4b692088a38f01f3b")})

结果：

{
"_id" : ObjectId("554a13d4b692088a38f01f3b"),
"title" : "product title",
"order" : 3,
"description" : "Description here ",
"status" : "live",
"tasks" : [ 
    {
        "title" : "task 1",
        "description" : "task 1 desc",
        "order" : 10,
        "_id" : ObjectId("554a13d4b692088a38f01f3a"),
        "status" : "live",
        "subTasks" : [ 
            {
                "title" : "task 1 sub 1",
                "content" : "aaa",
                "order" : -2,
                "_id" : ObjectId("554a13d4b692088a38f01f5a"),
                "status" : "live"
            }, 
            {
                "title" : "task 1 sub 2",
                "content" : "aaa",
                "order" : 1,
                "_id" : ObjectId("554a13d4b692088a38f01f3a"),
                "status" : "live"
            }, 
            {
                "title" : "task 1 sub 4",
                "content" : "aaa",
                "order" : 8,
                "_id" : ObjectId("554a13d4b692088a38f01f4a"),
                "status" : "live"
            }, 
            {
                "title" : "task 1 sub 3 ",
                "content" : "aaa",
                "order" : 2,
                "_id" : ObjectId("5550d0a61662211332d9a973"),
                "status" : "live"
            }
        ]
    }, 
    {
        "title" : "task 2",
        "description" : "task desc 2",
        "order" : 1,
        "_id" : ObjectId("5550855f9ee2db4e3958d299"),
        "status" : "live",
        "subTasks" : [ 
            {
                "title" : "task 2 sub 1",
                "content" : "bbb",
                "order" : 1,
                "_id" : ObjectId("55508f459ee2db4e3958d29a"),
                "status" : "live"
            }
        ]
    }, 
    {
        "title" : "task 3",
        "description" : "task 3 desc",
        "order" : 2,
        "_id" : ObjectId("5551b844bb343a620f85f323"),
        "status" : "live",
        "subTasks" : [ 
            {
                "title" : "task 3 sub 2",
                "content" : "cccc",
                "order" : 0,
                "_id" : ObjectId("5551b88abb343a620f85f324"),
                "status" : "live"
            }, 
            {
                "title" : "task 3 sub 4",
                "content" : "cccc",
                "order" : 1,
                "_id" : ObjectId("5551b8f1bb343a620f85f325"),
                "status" : "hidden"
            }, 
            {
                "title" : "task 3 sub 3",
                "content" : "ccc",
                "order" : 2,
                "_id" : ObjectId("5551ba40bb343a620f85f327"),
                "status" : "hidden"
            }, 
            {
                "title" : "task 3 sub 1",
                "content" : "cccc",
                "order" : -1,
                "_id" : ObjectId("5551bcb8c31283c051d30b7c"),
                "status" : "hidden"
            }
        ]
    }
]}

感谢n9code 上一个问题here，聚合管道非常适合排序任务和tasks.subTask（使用task.order 和task.subTasks.order）。

有时任务有没有子任务，例如：

{
"_id" : ObjectId("554a13d4b692088a38f01f3b"),
"title" : "product title",
"order" : 3,
"description" : "Description here ",
"status" : "live",
"tasks" : [ 
    {
        "title" : "task 1",
        "description" : "task 1 desc",
        "order" : 10,
        "_id" : ObjectId("554a13d4b692088a38f01f3a"),
        "status" : "live",
        "subTasks" : [ 
            {
                "title" : "task 1 sub 1",
                "content" : "aaa",
                "order" : -2,
                "_id" : ObjectId("554a13d4b692088a38f01f5a"),
                "status" : "live"
            }, 
            {
                "title" : "task 1 sub 2",
                "content" : "aaa",
                "order" : 1,
                "_id" : ObjectId("554a13d4b692088a38f01f3a"),
                "status" : "live"
            }, 
            {
                "title" : "task 1 sub 4",
                "content" : "aaa",
                "order" : 8,
                "_id" : ObjectId("554a13d4b692088a38f01f4a"),
                "status" : "live"
            }, 
            {
                "title" : "task 1 sub 3 ",
                "content" : "aaa",
                "order" : 2,
                "_id" : ObjectId("5550d0a61662211332d9a973"),
                "status" : "live"
            }
        ]
    }, 
    {
        "title" : "task 2",
        "description" : "task desc 2",
        "order" : 1,
        "_id" : ObjectId("5550855f9ee2db4e3958d299"),
        "status" : "live",
        "subTasks" : [ 

        ]
    }, 
    {
        "title" : "task 3",
        "description" : "task 3 desc",
        "order" : 2,
        "_id" : ObjectId("5551b844bb343a620f85f323"),
        "status" : "live",
        "subTasks" : [ 
            {
                "title" : "task 3 sub 2",
                "content" : "cccc",
                "order" : 0,
                "_id" : ObjectId("5551b88abb343a620f85f324"),
                "status" : "live"
            }, 
            {
                "title" : "task 3 sub 4",
                "content" : "cccc",
                "order" : 1,
                "_id" : ObjectId("5551b8f1bb343a620f85f325"),
                "status" : "hidden"
            }, 
            {
                "title" : "task 3 sub 3",
                "content" : "ccc",
                "order" : 2,
                "_id" : ObjectId("5551ba40bb343a620f85f327"),
                "status" : "hidden"
            }, 
            {
                "title" : "task 3 sub 1",
                "content" : "cccc",
                "order" : -1,
                "_id" : ObjectId("5551bcb8c31283c051d30b7c"),
                "status" : "hidden"
            }
        ]
    }
]
}

当他们没有孩子时，任何帮助让任务仍然显示？

当前聚合：

[
 {$match: {_id: ObjectId("554a13d4b692088a38f01f3b")}}, 
 {$project: {tasks: 1, doc: {title: "$title", order: "$order", description: "$description", status: "$status"}}}, 
 {$unwind: "$tasks"}, 
 {$unwind: "$tasks.subTasks"}, 
 {$sort: {"tasks.subTasks.order": 1, "tasks.order": 1}}, 
 {$project: {doc: 1, task_id: "$tasks._id", tasks_doc: {title: "$tasks.title", description: "$tasks.description", order: "$tasks.order", status: "$tasks.status"}, subTasks: "$tasks.subTasks"}}, 
 {$group: {_id: {_id: "$_id", task_id: "$task_id", doc: "$doc", task_doc: "$tasks_doc"}, subTasks: {$push: "$subTasks"}}}, 
 {$group: {_id: {_id: "$_id._id", doc: "$_id.doc"}, tasks: {$push: {_id: "$_id.task_id", title: "$_id.task_doc.title", description: "$_id.task_doc.description", order: "$_id.task_doc.order", status: "$_id.task_doc.status", subTasks: "$subTasks"}}}}, 
 {$project: {_id: "$_id._id", title: "$_id.doc.title", description: "$_id.doc.description", order: "$_id.doc.order", status: "$_id.doc.status", tasks: 1}}
]

想要的结果：

{
"_id": ObjectId("554a13d4b692088a38f01f3b"),
"title": "product title",
"order": 3,
"description": "Description here ",
"status": "live",
"tasks": [
    {
        "title": "task 2",
        "description": "task desc 2",
        "order": 1,
        "_id": ObjectId("5550855f9ee2db4e3958d299"),
        "status": "live",
        "subTasks": [

        ]
    },
    {
        "title": "task 3",
        "description": "task 3 desc",
        "order": 2,
        "_id": ObjectId("5551b844bb343a620f85f323"),
        "status": "live",
        "subTasks": [
            {
                "title": "task 3 sub 1",
                "content": "cccc",
                "order": -1,
                "_id": ObjectId("5551bcb8c31283c051d30b7c"),
                "status": "hidden"
            },
            {
                "title": "task 3 sub 2",
                "content": "cccc",
                "order": 0,
                "_id": ObjectId("5551b88abb343a620f85f324"),
                "status": "live"
            },
            {
                "title": "task 3 sub 3",
                "content": "ccc",
                "order": 2,
                "_id": ObjectId("5551ba40bb343a620f85f327"),
                "status": "hidden"
            }{
                "title": "task 3 sub 4",
                "content": "cccc",
                "order": 1,
                "_id": ObjectId("5551b8f1bb343a620f85f325"),
                "status": "hidden"
            }
        ]
    }{
        "title": "task 1",
        "description": "task 1 desc",
        "order": 10,
        "_id": ObjectId("554a13d4b692088a38f01f3a"),
        "status": "live",
        "subTasks": [
            {
                "title": "task 1 sub 1",
                "content": "aaa",
                "order": -2,
                "_id": ObjectId("554a13d4b692088a38f01f5a"),
                "status": "live"
            },
            {
                "title": "task 1 sub 2",
                "content": "aaa",
                "order": 1,
                "_id": ObjectId("554a13d4b692088a38f01f3a"),
                "status": "live"
            },
            {
                "title": "task 1 sub 3 ",
                "content": "aaa",
                "order": 2,
                "_id": ObjectId("5550d0a61662211332d9a973"),
                "status": "live"
            },
            {
                "title": "task 1 sub 4",
                "content": "aaa",
                "order": 8,
                "_id": ObjectId("554a13d4b692088a38f01f4a"),
                "status": "live"
            }
        ]
    }
]

【问题讨论】：

标签： mongodb mongoose aggregation-framework

【解决方案1】：

MongoDB 在$unwind 步骤中忽略空数组或空数组，因此首先您需要将空数组字段替换为某个值，例如"<e>"。

为此，只需在 $unwinding subTasks 之前添加此管道阶段：

$project: {
             doc: 1, 
             tasks: {
                       title: 1, 
                       description: 1, 
                       order: 1, 
                       status: 1, 
                       subTasks: {
                                    $cond: [
                                              {
                                                 $size: "$tasks.subTasks"
                                              }, 
                                              "$tasks.subTasks", 
                                              ['<e>']
                                           ]
                                 }
                     }
           }

然后，在 $grouping 期间，您需要做相反的事情，将您的 "<e>" 值替换为空数组：

$group: {
           _id: {
                   _id: "$_id._id", 
                   doc: "$_id.doc"}, 
                   tasks: {
                             $push: {
                                       _id: "$_id.task_id", 
                                       title: "$_id.task_doc.title", 
                                       description: "$_id.task_doc.description", 
                                       order: "$_id.task_doc.order", 
                                       status: "$_id.task_doc.status", 
                                       subTasks: {
                                                    $cond: [
                                                              {
                                                                 $eq: ["$subTasks", ["<e>"]]
                                                              }, 
                                                              [], 
                                                              "$subTasks"
                                                           ]
                                                  }
                                     }
                           }
                 }
         }

这是你的最终管道：

[
   {$match: {_id: ObjectId("554a13d4b692088a38f01f3b")}},
   {$project: {tasks: 1, doc: {title: "$title", order: "$order", description: "$description", status: "$status"}}},
   {$unwind: "$tasks"},
   {$project: {doc: 1, tasks: {title: 1, description: 1, order: 1, status: 1, subTasks: {$cond: [{$size: "$tasks.subTasks"}, "$tasks.subTasks", ['<e>']]}}}},
   {$unwind: "$tasks.subTasks"},
   {$sort: {"tasks.order": -1, "tasks.subTasks.order": 1}},
   {$project: {doc: 1, task_id: "$tasks._id", tasks_doc: {title: "$tasks.title", description: "$tasks.description", order: "$tasks.order", status: "$tasks.status"}, subTasks: "$tasks.subTasks"}},
   {$group: {_id: {_id: "$_id", task_id: "$task_id", doc: "$doc", task_doc: "$tasks_doc"}, subTasks: {$push: "$subTasks"}}},
   {$group: {_id: {_id: "$_id._id", doc: "$_id.doc"}, tasks: {$push: {_id: "$_id.task_id", title: "$_id.task_doc.title", description: "$_id.task_doc.description", order: "$_id.task_doc.order", status: "$_id.task_doc.status", subTasks: {$cond: [{$eq: ["$subTasks", ['<e>']]}, [], "$subTasks"]}}}}},
   {$project: {_id: "$_id._id", title: "$_id.doc.title", description: "$_id.doc.description", order: "$_id.doc.order", status: "$_id.doc.status", tasks: 1}}
]

干杯:)

【讨论】：

@MarkusWMahlberg 你找到问题了吗？ :)
遇到错误：uncaught exception: aggregate failed: { "errmsg" : "exception: Expression $eq takes exactly 2 arguments. 1 were passed in.", "code" : 16020, "ok" : 0 }
已修复。非常感谢@n9code 在这个问题上帮助我。他甚至通过聊天提供帮助！
更新为在最终输出中引入 task_id
你添加了id: 1，你的意思是_id: 1吗？如果是，则默认设置为这种方式，除非您指定_id: 0。