我有像 {'a': 1, 'z': {'b': 2, 'c': 3,}}
这样的文件.
I have documents like {'a': 1, 'z': {'b': 2, 'c': 3,}}
.
我想要 {'a': 1, 'b': 2, 'c': 3}
.
我可以用
aggregate({'$project': {'b': '$z.b', 'c': '$z.c'}})
是否可以在不手动列出子文档中的所有键的情况下做到这一点?
Is it possible to do it without listing all of the keys in the subdocument manually?
在 MongoDB 3.4 中,您可以使用 $objectToArray
和 $arrayToObject
与 $replaceRoot代码>为了改变这个:
With MongoDB 3.4 you can use $objectToArray
and $arrayToObject
with $replaceRoot
in order to change this:
db.wish.aggregate([
{ "$replaceRoot": {
"newRoot": {
"$arrayToObject": {
"$concatArrays": [
[{ "k": "a", "v": "$a" }],
{ "$objectToArray": "$z" }
]
}
}
}}
])
甚至连这么长的咒语都没有指定 "a"
属性:
Or even this long incantation without even specifying the "a"
property:
db.wish.aggregate([
{ "$replaceRoot": {
"newRoot": {
"$arrayToObject": {
"$reduce": {
"input": {
"$filter": {
"input": { "$objectToArray": "$$ROOT" },
"as": "r",
"cond": { "$ne": [ "$$r.k", "_id" ] }
}
},
"initialValue": [],
"in": {
"$concatArrays": [
"$$value",
{ "$cond": {
"if": { "$gt": [ "$$this.v", {} ] },
"then": { "$objectToArray": "$$this.v" },
"else": ["$$this"]
}}
]
}
}
}
}
}}
])
两者都产生:
{ "a" : 1, "b" : 2, "c" : 3 }
$concatArrays
的有趣用法在未来的版本中应该是不必要的,因为将会有一个 $mergeObjects
操作符,这会使它更简洁一些.
The funny use of $concatArrays
should not be necessary in future versions since there will be a $mergeObjects
operator which will make that a bit cleaner.
但您基本上可以非常简单地在客户端代码中执行相同的操作.例如在 JavaScript 中的 shell:
But you can basically just do the same thing in client code pretty simply. For example in JavaScript for the shell:
db.wish.find().map( doc => (
Object.assign({ a: doc.a }, doc.z )
))
或者是没有"a"
的版本:
db.wish.find().map( doc =>
Object.keys(doc).filter(k => k !== '_id').map(k =>
( typeof(doc[k]) === "object" ) ?
Object.keys(doc[k]).map(i => ({ [i]: doc[k][i] }))
.reduce((acc, curr) => Object.assign(acc,curr),{})
: { [k]: doc[k] }
).reduce((acc,curr) => Object.assign(acc,curr),{})
)
产生相同的输出
{ "a" : 1, "b" : 2, "c" : 3 }
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