Spring里面一对多的关系可以用@OnetoMany注解来实现
然后在实际使用中，如果要对从属对象按条件排序该怎么处理呢？可以用注解来实现的也就是@OrderBy
来看看我的这个例子
一个Product对象，里面有个OnetoMany关系对应到多张图片，然后我这个图片在后台要支持排序，所以我就在Picture这个类里面加了一个ordernum的int型字段来进行排序标记
@OneToMany(cascade = CascadeType.ALL,mappedBy = "product",fetch = FetchType.EAGER)
private List<Picture> pictures;然后我在取值的时候怎样才能让图片按照我的要求来进行排序呢
就是使用@OrderBy
看一下具体是怎么使用
@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface OrderBy {
String value() default "";
}通过这个注解的定义可以看出它的参数就是一个String
比如我项目里按照图片的ordernum升序排列就是@OrderBy("ordernum ASC");ordernum是字段名 ASC对应排序方式，中间用空格隔开
当然也支持多个条件进行排序，比如我要通过ordernum和id进行，那就是@OrderBy("ordernum ASC,id ASC")
最后我的代码
@OneToMany(cascade = CascadeType.ALL,mappedBy = "product",fetch = FetchType.EAGER)
@OrderBy("ordernum ASC")
private List<Picture> pictures;Entity One-to-Many 排序设置
@Entity
@Table(name = "TCOMMENT")
public class Comment {
@Id @GeneratedValue
private Long id;
private String nickname;
private String content;
private Integer note;
@Column(name = "posted_date")
@Temporal(TemporalType.TIMESTAMP)
private Date postedDate;
// Constructors, setters, getters
}
@Entity
@NamedQuery(name = "findAllNews", query = "SELECT n FROM News n")
public class News {
@Id @GeneratedValue
private Long id;
@Column(nullable = false)
private String content;
@OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.ALL})
@JoinTable(name = "NEWS_COMMENT", joinColumns = @JoinColumn(name = "NEWS_ID"),
inverseJoinColumns = @JoinColumn(name = "COMMENT_ID"))
@OrderBy("postedDate DESC")
private List<Comment> comments;
// Constructors, setters, getters
}
CREATE TABLE TCOMMENT (
ID BIGINT,
NICKNAME VARCHAR(50),
CONTENT VARCHAR(500),
NOTE INT,
POSTED_DATE TIMESTAMP,
PRIMARY KEY (ID)
);
CREATE TABLE NEWS (
ID BIGINT,
CONTENT VARCHAR(500),
PRIMARY KEY (ID)
);
CREATE TABLE NEWS_COMMENT (
NEWS_ID BIGINT,
COMMENT_ID BIGINT,
PRIMARY KEY (NEWS_ID, COMMENT_ID),
FOREIGN KEY (NEWS_ID) REFERENCES NEWS(ID),
FOREIGN KEY (COMMENT_ID) REFERENCES TCOMMENT(ID)
);以上为个人经验，希望能给大家一个参考，也希望大家多多支持编程网。
