来自MongoDB的随机文档使用spring-data [英] Random documents from MongoDB using spring-data

问题描述

我可以使用此 mongodb native query ：

db.books.aggregate(
   [ { $sample: { size: 15 } } ]
)

但如何在中执行此操作spring-data-mongodb ？

我在聚合类 spring-data / mongodb / docs / current / reference / html / #mongo.aggregationrel =nofollow> Spring Aggregation Framework

I found no similar operation in Aggregation class of Spring Aggregation Framework

推荐答案

更新：

从Spring Data v2.0开始，您可以这样做：

Starting with v2.0 of Spring Data you can do this:

SampleOperation matchStage = Aggregation.sample(5);
Aggregation aggregation = Aggregation.newAggregation(sampleStage);
AggregationResults<OutType> output = mongoTemplate.aggregate(aggregation, "collectionName", OutType.class);

---

原始答案：

像spring-mongo这样的抽象层总是落后于服务器发布的功能。所以你最好自己为管道阶段构建BSON文档结构。

Abstraction layers like spring-mongo are always going to lag way behind server released features. So you are best off contructing the BSON document structure for the pipeline stage yourself.

在自定义类中实现：

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);
    }
}

然后在你的代码中使用：

And then use in your code:

Aggregation aggregation = newAggregation(
    new CutomAggregationOperation(
        new BasicDBObject(
            "$sample",
            new BasicDBObject( "size", 15 )
        )
    )
);

由于这实现了 AggregationOperation 这适用于现有的管道操作辅助方法。 ie：

Since this implements AggregationOperation this works well with the exising pipeline operation helper methods. i.e:

Aggregation aggregation = newAggregation(
    // custom pipeline stage
    new CutomAggregationOperation(
        new BasicDBObject(
            "$sample",
            new BasicDBObject( "size", 15 )
        )
    ),
    // Standard match pipeline stage
    match(
        Criteria.where("myDate")
            .gte(new Date(new Long("949384052490")))
            .lte(new Date(new Long("1448257684431")))
    )
);

所以，一天结束时，一切都只是一个BSON对象。这只是一个接口包装器的问题，以便spring-mongo中的类方法解释结果并正确获取定义的BSON对象。

So again, everything is just a BSON Object at the end of the day. It's just a matter of having an interface wrapper so that the class methods in spring-mongo interpret the result and get your defined BSON Object correctly.

这篇关于来自MongoDB的随机文档使用spring-data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！