MongoDB-DBRef [英] MongoDB - DBRef

问题描述

我在使用 DBRef 时遇到了一些问题，请看这个案例:

I am having some troubles with DBRef, look this case:

db.fruit.save ({"_id" : "1" , "name" : "apple"});
db.fruit.save ({"_id" : "2" , "name" : "grape"});
db.fruit.save ({"_id" : "3" , "name" : "orange"});
db.fruit.save ({"_id" : "4" , "name" : "pineapple"});

db.basket.save ({"_id" : "1", "items" : [
    {"$ref" : "fruit", "$id" : "1", "quantity" : 5},
    {"$ref" : "fruit", "$id" : "3", "quantity" : 10}
]})

现在，让我们找到篮子"集合:

Now, lets find the "basket" collection:

> db.basket.find ()
{ "_id" : "1", "items" : [
    {
        "$ref" : "fruit",
        "$id" : "1"
    },
    {
        "$ref" : "fruit",
        "$id" : "3"
    }
] }

数量"属性消失了?！有人知道为什么吗?有替代品吗?

The "quantity" attribute disappeared ?! Anybody knows why ? Is there an alternative ?

谢谢.

推荐答案

dbref 是

  { $ref : <collname>, $id : <idvalue>[, $db : <dbname>] }

但是您在 dbref 中添加了不受支持的数量字段.那就是问题所在.把它带到外面

But you have added non-supported quantity field inside dbref. Thats the problem. take that outside

db.basket.save ({"_id" : "1", "items" : [
    {"quantity" : 5 , item : {"$ref" : "fruit", "$id" : "1"}},
    {"quantity" : 10, item : {"$ref" : "fruit", "$id" : "3"}}
]})

什么样的样子(吓人)

{
    "_id" : "1",
    "items" : [
        {
            "quantity" : 5,
            "item" : {
                "$ref" : "fruit",
                "$id" : "1"
            }
        },
        {
            "quantity" : 10,
            "item" : {
                "$ref" : "fruit",
                "$id" : "3"
            }
        }
    ]
}

但我的建议是，完全放弃 dbref，只使用像这样的简单结构

But my advice is, ditch the dbref altogether and just use the simple structure like this

db.basket.save ({"_id" : "1",items:[
                        {item_id:"1",quantity:50},
                        {item_id:"3",quantity:10}
                ]})

这更干净，看起来像

{
    "_id" : "1",
    "items" : [
        {
            "item_id" : "1",
            "quantity" : 50
        },
        {
            "item_id" : "3",
            "quantity" : 10
        }
    ]
}

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