按数组类型查询 - MongoDB [英] Query by array type - MongoDB

问题描述

我必须按类型查询我的 mongoDB 集合.
假设我有这两个 hello 集合的文档:

I have to query my mongoDB collection by type.
Suppose I have these two documents of hello collection:

{
        "_id" : ObjectId("56684ee0f597654b99d0d636"),
        "name" : "Scrooge",
        "surname" : "McDuck",
        "address" : {
                "road" : "Money Bin",
                "number" : 19
        },
        "hobbies" : [
                "money",
                "food",
                "cooking"
        ]
}
{
        "_id" : ObjectId("66684ee0f597654b99d0d636"),
        "name" : "Mickey",
        "surname" : "Mouse",
        "address" : {
                "road" : "Topolinia",
                "number" : 34
        },
        "hobbies" : [
                "minnie",
                "cheese"
        ]
}

现在，如果我按数组类型查询:

Now, if I query by array type:

db.hello.find({hobbies: {$type: 4 }})

我在输出中没有任何文档.如您所见，此处 4 是数组类型的数量.

I don't have any documents in output. As you can see here 4 is the number of array type.

推荐答案

这是预期的行为.您可以使用 "dot notation" 和$exists 运算符

This is the expected behaviour. You can simply do this using the "dot notation" and the $exists operator

db.hello.find({ 'hobbies.0': { '$exists': true } } )

另一种方法是使用聚合和 $isArray 操作符在 MongoDB 3.2 中可用.但这效率较低，因为 $redact 进行集合扫描.

Another way to do this is by using aggregation and the $isArray operator available in MongoDB 3.2. But this is less efficient because $redact does a collection scan.

 db.hello.aggregate([ 
    { "$redact": { 
        "$cond": [
             { $isArray: "$hobbies" }, 
             "$$KEEP", 
             "$$PRUNE" 
        ]
    }}
])

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