Question

该数据库接近5GB。我有这样的文件:

{
    _id: ..
    user: "a"
    hobbies: [{
        _id: ..
        name: football
    },
    {
        _id: ..
        name: beer
    }
    ...
    ]
}

I want to return users who have more then 0 "hobbies" I ve tried

db.collection.find({"hobbies" : { &gt : 0}}).limit(10)

并且不产生任何结果。

How to do conduct this select?
And how to return only: id, name, count ?
How to do it with c# official driver?

TIA

P.S. near i ve found: "Add new field to hande category size. It s a usual practice in mongo world." is this true?

Answer 1

您是否使用<代码>。 i n t 测试了这一情况,但我认为,这是正确的方式,可以质疑中贡布阵列的范围。

db.collection.find({$where:  (this.hobbies.length > 0) })

Answer 2

在这种具体情况下,你可以使用清单索引解决你的问题:

db. Collection.find({>hobbies.0>:{$exists : real>limit(10)/code>



这确保了第一点内容。 你也可以这样做,通过在范围结束时核对现有要素,确保清单缩短到零之间或x之间和 y之间。

Answer 3

您可以(简短)对<代码>size的一系列阵列长度进行检查。运营商使用逻辑<代码>$not:

db.collection.find({array: {$not: {$size: 0}}})

Answer 4

这一点有些真实。

根据手册

数额

The 数额 operator matches any array with the specified number of elements. The following example would match the object {a:["foo"]}, since that array has just one element:

db.things.find( { a : { 数额: 1 } } );

You cannot use 数额 to find a range of sizes (for example: arrays with more than 1 element). If you need to query for a range, create an extra size field that you increment when you add elements

因此,你可以检查面积为0,但不能检查面积大于0的情况。

Answer 5

先前的问题解释了如何处理阵列计问题。虽然在您的案例中,如果国际移民组织确实是你想要检验的唯一价值,那么当它空洞并选择不将其序列化时,你就可以将阵列定为无效,但你可以检验这个领域的存在。当你想给用户增加一只ho子时,应自行测试无效并创建阵列。

就第2号而言,如果你增加了计算点,就很容易从数据库中选择你想要回的领域,并包括计票场。

Answer 6

if you need to find only zero hobbies, and if the hobbies key is not set for someone with zero hobbies , use EXISTS flag. Add an index on "hobbies" for performance enhancement :

db. 收集.find({ho:{ $:真});
但是,如果拥有零栖息地的人有空阵,而有1个ho子的人有一阵列,有1个元素,则使用这一通用解决办法:

Maintain a variable called "hcount" ( hobby count), and always set it equal to size of hobbies array in any update. Index on the field "hcount" Then, you can do a query like :

 db.collection.find( { hcount : 0 } ) // people with 0 hobbies    
 db.collection.find( { hcount : 5 } ) // people with 5 hobbies

3 - From @JohnPs answer, "$size" is also a good operator for this purpose. http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24size

友情链接