在Spring Mongo中使用$ stdDevSamp或$ stdDevPop [英] Use $stdDevSamp or $stdDevPop with Spring Mongo

问题描述

我想知道如何实现在Spring Mongo Data中使用的标准偏差聚合函数.

I'd like to know how to implement a Standard Deviation aggregation Function to use in Spring Mongo Data.

我知道Mongo DB 3.2具有标准偏差聚合功能，但是在Spring Data中不可用.

I Know Mongo DB 3.2 has a Standard Deviation aggregation function, but It isn't available in Spring Data.

我可以使用Mongo的汇总功能吗?

Could I use the Mongo's aggregation function?

谢谢.

推荐答案

不可用" 和未实现辅助方法" 之间有明显的区别，这就是实际情况.只是因为没有用于实现 $stdDevSamp 的帮助器"或 $stdDevPop 运算符，并不意味着它们无法使用，当然，只要您连接到MongoDB 3.2实例即可.

There is a distinct difference between "not available" and "no implemented helper method", and that is the real case here. Just because there is no "helper" for implementing the $stdDevSamp or $stdDevPop operators, does not mean they cannot be used, as long as you are connecting to a MongoDB 3.2 instance of course.

您真正需要的是一个支持AggregationOperation接口的自定义类，该类允许使用DBObject进行构造:

All you really need is a custom class supporting the AggregationOperation interface, that will allow construction using DBObject:

public class CustomAggregationOperation implements AggregationOperation {
    private DBObject operation;

    public CustomAggregationOperation (DBObject operation) {
        this.operation = operation;
    }

    @Override
    public DBObject toDBObject(AggregationOperationContext context) {
        return context.getMappedObject(operation);
    }
}

然后您可以在聚合管道构建中使用该类，如下所示:

Then you can use that class in aggregation pipeline construction like so:

Aggregation aggregation = newAggregation(
    new CustomAggregationOperation(
        new BasicDBObject("$sample", new BasicDBObject("size",100))
    ),
    new CustomAggregationOperation(
        new BasicDBObject(
            "$group",
            new BasicDBObject("_id",null)
                .append("ageStdDev",new BasicDBObject("$stdDevSamp","$age"))
        )
    )
);

这相当于文档示例 :

db.users.aggregate(
   [
      { "$sample": { "size": 100 } },
      { "$group": { "_id": null, "ageStdDev": { "$stdDevSamp": "$age" } } }
   ]
)

作为AggregationOperation的接口，该类可以轻松地与已实现的帮助程序混合:

As an interface for AggregationOperation the class easily mixes with the implemented helpers:

Aggregation aggregation = newAggregation(
    // Using the match helper for the `$match` stage
    match(
        Criteria.where("age").gte(20).lte(50)
    ),
    // Mixed in with custom classes for the others
    new CustomAggregationOperation(
        new BasicDBObject("$sample", new BasicDBObject("size",100))
    ),
    new CustomAggregationOperation(
        new BasicDBObject(
            "$group",
            new BasicDBObject("_id",null)
                .append("ageStdDev",new BasicDBObject("$stdDevSamp","$age"))
        )
    )
);

因此，即使没有帮手"，您仍然可以使用功能来为您制定BSON对象构造.您只需要自己进行构建即可.

So you can still use features even if there is no "buit in helper" to work out the BSON Object construction for you. You just do the construction yourself.

这篇关于在Spring Mongo中使用$ stdDevSamp或$ stdDevPop的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！