查询 MongoDB 中的嵌入文档

Question

我有一个 Bson，其中包含一些遵循以下结构的嵌入文档。我想知道如何获取特定日期的变量值（“2014-08-09”：53.0）或库存值（“2014-08-09”：0.0） .

{
    "_id" : ,
    "last_modified" : "",
    "client" : "",
    "credentials" : [],
    "tags" : [],
    "variables" : [ 
        {
            "name" : "sales",
            "_values" : {
                "2014-08-09" : 53.0,
                ...
            },
            "tags" : [],
            "is_target" : true,
            "method1" : "",
            "method2" : "",
            "vtype" : ,
            "index_type" : 
        }, 
        {
            "name" : "inventory",
            "_values" : {
                "2014-08-09" : 0.0,
                ...
            },
            "tags" : [],
            "is_target" : ,
            "method1" : "",
            "method2" : "",
            "vtype" : ,
            "index_type" : 
        }, 
        {
            "name" : "price",
            "_values" : {},
            "tags" : [],
            "is_target" : ,
            "method2" : "",
            "method1" : "",
            "vtype" : ,
            "index_type" : 
        }
    }
} 

Answer 1

尝试使用 mongodb 聚合框架 https://docs.mongodb.com/manual/reference/operator/aggregation/

db.mycol.aggregate([
    {"$unwind":"$variables"},
    {$project:{"date":"$variables._values.2014-08-09"}}
])