Question

我试图在一个查询中返回一组平均值和一组评分。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);

但是，只要我想在同一个查询中获得平均值和一个计数，就会遇到麻烦。经过几个小时的实验，我发现这很有效，所以我在这里分享。我希望它有所帮助。

1）我需要一个新的结果类：

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);

现在，一个查询会返回平均评分和评分计数

Answer 1

解决了自己。

接收结果的自定义类：

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);

Answer 2

感谢。

你应该防止NPE和hibernate解析元组错误如下：

public class AggregateResults {

private final double rating;
private final int totalRatings;

public AggregateResults(Double rating, Long totalRatings) {
    this.rating = rating == null ? 0 : rating;
    this.totalRatings = totalRatings == null ? 0 : totalRatings.intValue();
}

public double getRating() {
    return rating;
}
public int getTotalRatings() {
    return totalRatings;
}}

Spring Data JPA - 结果

2 个答案: