如何在子属性上使用$ setIsSubset（或其他set操作）

Question

我遇到的是一个非常简单的问题，我只是想念一些东西，所以希望有人能指出我要去哪里。我正在尝试使用$ setIsSubset操作引用一个包含项列表的子属性，但它告诉我它为null。基本上查询是错误的，但我不明白为什么。这是Mongo shell的输出：

$ mongo setTest
MongoDB shell version: 2.6.3
connecting to: setTest
> db.items.insert({"credentials":{"authorities":["AUTH1"]}});
WriteResult({ "nInserted" : 1 })
> db.items.find();
{ "_id" : ObjectId("53acd0e214c4ee1272550de4"), "credentials" : { "authorities" : [ "AUTH1" ] } }
> var userAuthorities = ["AUTH1","AUTH2","AUTH3"];
> db.items.aggregate([
...     { $redact:
...         {
...            $cond:
...               {
...                  if: { $setIsSubset: ["$credentials.authorities", userAuthorities ] },
...                  then: "$$DESCEND",
...                  else: "$$PRUNE"
...               }
...         }
...      }
... ]);
assert: command failed: {
    "errmsg" : "exception: both operands of $setIsSubset must be arrays. First argument is of type: EOO",
    "code" : 17310,
    "ok" : 0
} : aggregate failed
Error: command failed: {
    "errmsg" : "exception: both operands of $setIsSubset must be arrays. First argument is of type: EOO",
    "code" : 17310,
    "ok" : 0
} : aggregate failed
    at Error (<anonymous>)
    at doassert (src/mongo/shell/assert.js:11:14)
    at Function.assert.commandWorked (src/mongo/shell/assert.js:244:5)
    at DBCollection.aggregate (src/mongo/shell/collection.js:1149:12)
    at (shell):1:10
2014-06-26T20:04:54.465-0600 Error: command failed: {
    "errmsg" : "exception: both operands of $setIsSubset must be arrays. First argument is of type: EOO",
    "code" : 17310,
    "ok" : 0
} : aggregate failed at src/mongo/shell/assert.js:13
>

谁能看到我在做什么错？

Answer 1

您的问题不是集合运算符本身，而是您对的理解$redact。

该$redact流水线阶段递归遍历文档测试的字段值所以这里的问题是，你所引用的阵列相匹配的方式是不确实出现在“当前深度”所有的时间。

您有几种方法可以解决此问题。要么先进行操作，以确保使用所有深度在所有深度存在一个数组$project：

var userAuthorities = ["AUTH1","AUTH2","AUTH3"];

db.items.aggregate([
    { "$project": {
        "credentials": 1,
        "authorities": { "$literal": [] }
    }},
    { "$redact": {
        "$cond": {
            "if": { "$setIsSubset": [ "$authorities", userAuthorities ] },
            "then": "$$DESCEND",
            "else": "$$PRUNE"
        }                    
    }}
])

或测试是否存在该字段，并通过$ifNull以下方式在线替换为空数组：

db.items.aggregate([
    { "$redact": {
        "$cond": {
            "if": { 
                "$setIsSubset": [ 
                    { "$ifNull": [ "$authorities", { "$literal": [] } ]},
                    userAuthorities
                ]
            },
            "then": "$$DESCEND",
            "else": "$$PRUNE"
        }                    
    }}
])

或者最后只是始终接受您正在使用$$ROOT比较。但是有点失败的目的$redact

db.items.aggregate([
    { "$redact": {
        "$cond": {
            "if": { 
                "$setIsSubset": [ 
                    "$$ROOT.credentials.authories"
                    userAuthorities
                ]
            },
            "then": "$$DESCEND",
            "else": "$$PRUNE"
        }                    
    }}
])

但基本上说来，与的比较$redact是相对于当前降级到的文档的级别。因此，您的变量比较也必须考虑这一点。