如何查询Spring JPA中的引用表

Question

我有两个表 Item 和 Review Item class

@Entity
public class Item {

  @Id
  @GeneratedValue
  private Long id;

  @Column(length = 100)
  @NotEmpty
  private String title;

  @Column(length = 200)
  private String description;

  @OneToMany(mappedBy = "item", cascade = CascadeType.ALL, orphanRemoval = true)
  Set<Review> reviews = new HashSet<>();

  public Item() {
  }

  public Item(String title, String description) {
    this.title = title;
    this.description = description;
  }

  public Long getId() {
    return id;
  }

  public String getTitle() {
    return title;
  }

  public String getDescription() {
    return description;
  }

  public Set<Review> getReviews() {
    return reviews;
  }

  public void addReview(Review review) {
    reviews.add(review);
    review.setItem(this);
  }

  @Override
  public String toString() {
    return "\nItem{" +
        "id=" + id +
        ", title='" + title + '\'' +
        ", description='" + description + '\'' +
        ", reviews=" + reviews +
        '}';
  }
}

审查表

@Entity
public class Review {

  @Id
  @GeneratedValue
  private Long id;

  private Double rating;

  @Length(max=200)
  private String comment;

  @ManyToOne(optional = false)
  private Item item;

  @ManyToOne(optional = false)
  private User author;

  public Review() {
  }

  public Review(Double rating, String comment, User author) {
    this.rating = rating;
    this.comment = comment;
    this.author = author;
  }

  public Long getId() {
    return id;
  }

  public Double getRating() {
    return rating;
  }

  public String getComment() {
    return comment;
  }

  public Item getItem() {
    return item;
  }

  public User getAuthor() {
    return author;
  }

  void setItem(Item item) {
    this.item = item;
  }

  @Override
  public String toString() {
    return "\nReview{" +
        "id=" + id +
        ", rating=" + rating +
        ", comment='" + comment + '\'' +
        '}';
  }
}

我想使用 Spring JPA 编写查询来查找平均评分低于例如 (6) 的项目。 单个项目将有多个评级，因此特定项目的平均评级应小于 6。我尝试了很多方法但无法计算。

public interface ItemRepository extends CrudRepository<Item, Long> {

    @Query(
              value = "SELECT i FROM Item i where (select AVG(rating) from Review where rating < :rating) > :rating", 
              nativeQuery = true)
    List<Item> findItemsWithAverageRatingLowerThan(@Param("rating") Double rating);
    
}

请纠正我出错的地方。

Answer 1

我不明白这部分

特定项目的平均评分应小于 6

但简单地说，您将 JPQL 语法与本机 SQL 语法混合在一起。 当您使用函数或特定的 SQL 运算符时，本机版本仅为 go：

SELECT * FROM ITEM i JOIN REVIEW r ON i.id = r.item_id where AVG(r.rating) < :rating

Answer 2

1. 您需要使用 JPQL 查询语言。 所以删除nativeQuery = true
2. 在子查询中执行Item和Review表的连接

查询示例：

@Repository
public interface ItemRepository extends CrudRepository<Item, Long> {
    @Query(value = "SELECT i FROM Item i where (select AVG(r.rating) FROM Review r where r.item = i) < :rating")
    List<Item> findItemsWithAverageRatingLowerThan(@Param("rating") Double rating);
}

测试数据：

insert into item(id, description, title) values(1, 'description', 'title1');
insert into item(id, description, title) values(2, 'description', 'title2');

insert into review(id, rating, comment, item_id) values(1, 3, 'comment', 1);
insert into review(id, rating, comment, item_id) values(2, 3, 'comment', 1);
insert into review(id, rating, comment, item_id) values(3, 3, 'comment', 1);

insert into review(id, rating, comment, item_id) values(4, 30, 'comment', 2);
insert into review(id, rating, comment, item_id) values(5, 3, 'comment', 2);
insert into review(id, rating, comment, item_id) values(6, 15, 'comment', 2);

输入值： 6
Output： id = 1 的项目实体
查询返回 AVG Review 评分小于 6 的项目

Hibernate 生成本机查询：

    select
        item0_.id as id1_1_,
        item0_.description as descript2_1_,
        item0_.title as title3_1_ 
    from
        item item0_ 
    where
        (
            select
                avg(review1_.rating) 
            from
                review review1_ 
            where
                review1_.item_id=item0_.id
        )<?