Mongo：合并子文档并在字段中引用父级

Question

我有以下mongo集合：

{
    "_id" : ObjectId("000000000001"),
    "username" : "user1",
    "password" : "password",
    "alerts" : [ 
        {
            "_id" : ObjectId("5947a8d3b5ac80946b7ee4bd"),
            "direction" : "rise",
            "threshold" : "1000",
            "notified" : true,
            "notified_when" : null
        }, 
        {
            "_id" : ObjectId("5947a8d8b5ac80946b7ee4be"),
            "direction" : "rise",
            "threshold" : "1200",
            "notified" : false,
            "notified_when" : null
        }
    ]
},
{
    "_id" : ObjectId("000000000002"),
    "username" : "user2",
    "password" : "password",
    "alerts" : [
        {
            "_id" : ObjectId("5947a8d3b5ac80946b7ee4bd"),
            "direction" : "rise",
            "threshold" : "1000",
            "notified" : true,
            "notified_when" : null
        }
    ]
},
{
    "_id" : ObjectId("000000000003"),
    "username" : "user3",
    "password" : "password",
    "alerts" : []
}

我只想选择alerts对象，然后将它们合并在一起。 如果可能的话，我想将父用户的_id字段注入每个alert 。

我可以用普通的javascript做到这一点，但我想知道MongoDB是否可行。

结果将是：

[
    {
        "_id" : ObjectId("5947a8d3b5ac80946b7ee4bd"),
        "direction" : "rise",
        "threshold" : "1000",
        "notified" : true,
        "notified_when" : null,
        "parent_id": ObjectId("000000000001")
    }, 
    {
        "_id" : ObjectId("5947a8d8b5ac80946b7ee4be"),
        "direction" : "rise",
        "threshold" : "1200",
        "notified" : false,
        "notified_when" : null,
        "parent_id": ObjectId("000000000001")
    },
    {
        "_id" : ObjectId("5947a8d3b5ac80946b7ee4bd"),
        "direction" : "rise",
        "threshold" : "1000",
        "notified" : true,
        "notified_when" : null,
        "parent_id": ObjectId("000000000002")
    }
]

提前致谢

Answer 1

您可以使用聚合来实现。 首先展开警报数组，然后投影必填字段。 展开解构数组，并为每个数组元素返回一个文档。

db.collection.aggregate(
{$unwind: '$alerts'},
{$project:  {
        "_id" : '$alerts._id',
        "direction" : "$alerts.direction",
        "threshold" : "$alerts.threshold",
        "notified" : '$alerts.notified',
        "notified_when" : '$alerts.notified_when',
        "parent_id": '$_id'
    }}
)