Question

这适用于文档跟踪/管理系统，系统将跟踪文档的状态。文件状态包括＆＃34;注册＆＃34;，＆＃34;背书＆＃34;，＆＃34;未跟踪＆＃34;等等...在我的mongodb中，每个文档状态更改都会在mongodb中有一个条目..

以下是doc状态的示例集合：

[//FOR DOCUMENT ONE
    {
        "document": "doc1",
        "stateName": "enrolled",
        "when": ISODate("a date when the doc state changed")
    },
    {
        "document": "doc1",
        "stateName": "mark-for-review",
        "when": ISODate("a date when the doc state changed")
    },
    {
        "document": "doc1",
        "stateName": "endorsed",
        "when": ISODate("a date when the doc state changed")
    },
    //FOR DOCUMENT TWO
    {
        "document": "doc2",
        "stateName": "endorsed",
        "when": ISODate("a date when the doc state changed")
    },
    {
        "document": "doc2",
        "stateName": "untracked",
        "when": ISODate("a date when the doc state changed")
    }
]

现在我希望能够查询上述集合并获得如下结果：

[
    {
        "id" : "doc1",
        "state" : "endorsed"  // this should be based on the latest changed of the document1 from the 'when' column
    },
    {
        "id" : "doc2",
        "state" : "untracked" // this should be based on the latest changed of the document2 from the 'when' column
    },
]

使用聚合，我可以在文档发生变化时查询最新日期（＆＃34;当＆＃34;字段），但我不知道如何包含文档的实际状态，例如＆＃34;已注册＆＃ 34;，＆＃34;未跟踪＆＃34;等等。

Answer 1

$sort when文档按降序排列，$group按文档排序，并从中获取$first州

db.col.aggregate(
    [
        {$sort : {"when" : -1}},
        {$group : {_id : "$document", state : {$first : "$stateName"}}}
    ]
)

或按升序排序并采取最后状态

文档跟踪，Mongodb查询最新文档状态

1 个答案: