java - Spring Data JPA - 结果中具有多个聚合函数的自定义查询

Question

我试图在一个查询中返回一组评分的平均值和计数。 在我发现浏览的示例之后，我在两个查询中相当容易地管理它。例如:

@Query("SELECT AVG(rating) from UserVideoRating where videoId=:videoId")
public double findAverageByVideoId(@Param("videoId") long videoId);

但只要我想在同一个查询中计算平均值和计数，问题就开始了。经过几个小时的实验，我发现这很有效，所以我在这里分享它。希望对你有帮助。

1) 我需要一个新的类来获得结果:

我必须在查询中引用该类:

@Query("SELECT new org.magnum.mobilecloud.video.model.AggregateResults(AVG(rating) as rating, COUNT(rating) as TotalRatings) from UserVideoRating where videoId=:videoId")
public AggregateResults findAvgRatingByVideoId(@Param("videoId") long videoId);

一个查询现在返回平均评分和评分计数

Answer 1

自己解决了。

自定义类接收结果:

public class AggregateResults {

    private final double rating;
    private final int totalRatings;

    public AggregateResults(double rating, long totalRatings) {
        this.rating = rating;
        this.totalRatings = (int) totalRatings;
    }

    public double getRating() {
        return rating;
    }

    public int getTotalRatings() {
        return totalRatings;
    }
}

和

@Query("SELECT new org.magnum.mobilecloud.video.model.AggregateResults(
    AVG(rating) as rating, 
    COUNT(rating) as TotalRatings) 
    FROM UserVideoRating
    WHERE videoId=:videoId")
public AggregateResults findAvgRatingByVideoId(@Param("videoId") long videoId);