一個(gè)Product對(duì)象，里面有個(gè)OnetoMany關(guān)系對(duì)應(yīng)到多張圖片，然后我這個(gè)圖片在后臺(tái)要支持排序，所以我就在Picture這個(gè)類里面加了一個(gè)ordernum的int型字段來(lái)進(jìn)行排序標(biāo)記

@OneToMany(cascade = CascadeType.ALL,mappedBy = "product",fetch = FetchType.EAGER)
private List<Picture> pictures;

然后我在取值的時(shí)候怎樣才能讓圖片按照我的要求來(lái)進(jìn)行排序呢

就是使用@OrderBy

看一下具體是怎么使用

@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface OrderBy { 
   /**
    * An <code>orderby_list</code>.  Specified as follows:
    *
    * <pre>
    *    orderby_list::= orderby_item [,orderby_item]*
    *    orderby_item::= [property_or_field_name] [ASC | DESC]
    * </pre>
    *
    * <p> If <code>ASC</code> or <code>DESC</code> is not specified,
    * <code>ASC</code> (ascending order) is assumed.
    *
    * <p> If the ordering element is not specified, ordering by
    * the primary key of the associated entity is assumed.
    */
    String value() default "";
}

通過(guò)這個(gè)注解的定義可以看出它的參數(shù)就是一個(gè)String

比如我項(xiàng)目里按照?qǐng)D片的ordernum升序排列就是@OrderBy("ordernum ASC");ordernum是字段名 ASC對(duì)應(yīng)排序方式，中間用空格隔開(kāi)

當(dāng)然也支持多個(gè)條件進(jìn)行排序，比如我要通過(guò)ordernum和id進(jìn)行，那就是@OrderBy("ordernum ASC,id ASC")

最后我的代碼

@OneToMany(cascade = CascadeType.ALL,mappedBy = "product",fetch = FetchType.EAGER)
@OrderBy("ordernum ASC")
private List<Picture> pictures;

Entity One-to-Many 排序設(shè)置

/**
 * 評(píng)論實(shí)體類，對(duì)應(yīng) TCOMMENT 表。
 * @author William
 */
@Entity
@Table(name = "TCOMMENT")
public class Comment {
 
 /**
  * 標(biāo)識(shí)ID字段為主鍵，主鍵生成策略為：自動(dòng)。
  */
 @Id @GeneratedValue
 private Long id;
 private String nickname;
 private String content;
 private Integer note;
 /**
  * 發(fā)表日期，對(duì)應(yīng) posted_date 字段，字段類型為TIMESTAMP。
  */
 @Column(name = "posted_date")
 @Temporal(TemporalType.TIMESTAMP)
 private Date postedDate;
 
 // Constructors, setters, getters
}

/**
 * 新聞實(shí)體類，對(duì)應(yīng) News表。
 * @author William
 */
@Entity
@NamedQuery(name = "findAllNews", query = "SELECT n FROM News n")
public class News {
 
 /**
  * 標(biāo)識(shí)ID字段為主鍵，主鍵生成策略為：自動(dòng)。
  */
 @Id @GeneratedValue
 private Long id;
 /**
  * content新聞內(nèi)容，該字段必填。
  */
 @Column(nullable = false)
 private String content;
 /**
  * comments評(píng)論，與之進(jìn)行一對(duì)多關(guān)聯(lián)。<br/>
  * FetchType.EAGER 獲取新聞時(shí)立即相關(guān)評(píng)論。<br/>
  * CascadeType.ALL 支持所有級(jí)聯(lián)操作。<br/>
  * OrderBy 獲取評(píng)論列表時(shí)，按照postedDate（發(fā)表日期）降序排列。
  */
 @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)
);

以上為個(gè)人經(jīng)驗(yàn)，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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