MongoDB - DBRef [英] MongoDB - DBRef
问题描述
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:菠萝});
$ b $ db.basket.save({_id:1,items:[
{$ ref:fruit,$ id:1 ,数量:
{$ ref:fruit,$ id:3,quantity:10}
]})
现在,让我们找到篮子集合:
> 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?有没有其他的选择?
谢谢。
dbref 是
<$ p $ {$ 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。外面拿着那个
db.basket.save({_id:1,items:[
{quantity:5,item:{$ ref:fruit,$ id:1}},
{quantity:10,item:{$ ref fruit,$ id:3}}
]})
(可怕)
{
_id:1,
:[
quantity:5,
item:{
$ ref:fruit,
$ id: 1
},
{
quantity:10,
item:{
$ ref:fruit,
$ id:3
}
}
]
}
但是我的建议是,把dbref完全抛在一边,用这个简单的结构
db.basket.save({_id:1,items:[
{item_id:1,quantity:50},
{item_id:3,quantity:10}
]})
清洁剂,看起来像
{
_id:1,
items :[
item_id:1,
quantity:50
},
{
item_id:3 ,
quantity:10
}
]
}
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}
]})
Now, lets find the "basket" collection:
> db.basket.find ()
{ "_id" : "1", "items" : [
{
"$ref" : "fruit",
"$id" : "1"
},
{
"$ref" : "fruit",
"$id" : "3"
}
] }
The "quantity" attribute disappeared ?! Anybody knows why ? Is there an alternative ?
Thanks.
Syntax for the dbref is
{ $ref : <collname>, $id : <idvalue>[, $db : <dbname>] }
But you have added non-supported quantity field inside dbref. Thats the problem. take that outside
db.basket.save ({"_id" : "1", "items" : [
{"quantity" : 5 , item : {"$ref" : "fruit", "$id" : "1"}},
{"quantity" : 10, item : {"$ref" : "fruit", "$id" : "3"}}
]})
which kind of looks (scary)
{
"_id" : "1",
"items" : [
{
"quantity" : 5,
"item" : {
"$ref" : "fruit",
"$id" : "1"
}
},
{
"quantity" : 10,
"item" : {
"$ref" : "fruit",
"$id" : "3"
}
}
]
}
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}
]})
this is much cleaner, which will look like
{
"_id" : "1",
"items" : [
{
"item_id" : "1",
"quantity" : 50
},
{
"item_id" : "3",
"quantity" : 10
}
]
}
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