抽象 class 和 Spring 的問題

Question

我正在開發一個基於 Spring 框架的簡單 webapp。 我有這兩個文件是映射數據庫表的響應：

import javax.persistence.*;
import java.util.Date;

/**
 * Abstract class for all publications of BIS
 * @author Tomek Zaremba
 */

public abstract class GenericPost {

@Temporal(TemporalType.DATE)
@Column(name = "date_added")
private Date dateAdded;

@Column(name = "title")
private String title;

@Column(name = "description")
private String description;

/**
 *
 * @return title of publication
 */
public String getTitle() {
    return title;
}

/**
 *
 * @param title to be set for publication
 */
public void setTitle(String title) {
    this.title = title;
}

/**
 *
 * @return description of publication
 */
public String getDescription() {
    return description;
}

/**
 *
 * @param description of publication
 */
public void setDescription(String description) {
    this.description = description;
}

/**
 *
 * @return date when publication was added
 */
public Date getDateAdded() {
    return dateAdded;
}

/**
 *
 * @param dateAdded set the date of adding for publication
 */
public void setDateAdded(Date dateAdded) {
    this.dateAdded = dateAdded;
}
}

另一個：

import javax.persistence.*;
import java.io.Serializable;

/**
 * Instances of Link represents and collects data about single link stored in BIS    database
 * @author Tomek Zaremba
 */
@Entity
@Table(name="Link", schema="public")
public class Link extends GenericPost implements Serializable{

@Id
@Column(name="id", unique=true)
@GeneratedValue(strategy= GenerationType.SEQUENCE, generator="link_id_seq")
@SequenceGenerator(sequenceName="link_id_seq", name="link_id_seq")
private Integer id;

@Column(name="link")
private String link;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "author_user_id")
private User user;

/**
 *
 * @return id of link
 */
public Integer getId() {
    return id;
}

/**
 *
 * @param id to be set to link
 */
public void setId(Integer id) {
    this.id = id;
}

/**
 *
 * @return link which is connected with Link instance
 */
public String getLink() {
    return link;
}

/**
 *
 * @param link to be set fo Link instance
 */
public void setLink(String link) {
    this.link = link;
}

/**
 *
 * @return User instance connected with Link instance
 */
public User getUser() {
    return user;
}

/**
 *
 * @param user to be set for Link instance
 */
public void setUser(User user) {
    this.user = user;
}
}

問題是：為什么當我使用通用 class（吸氣劑）中的方法時，我總是得到 null 而當我使用來自鏈接 class 的吸氣劑時，我得到正確的數據？ 數據庫訪問很好，junit 測試通過，沒有錯誤。 感謝幫助。

Answer 1

GenericPost class 應該用@MappedSuperclass注釋。 否則，映射不會考慮其持久性注釋。

注意：您的單元測試可能應該更新以檢查超類字段的映射是否按預期工作。

Answer 2

我不認為這是春天的錯。 您需要使用 @MappedSuperclass 注釋您的父@MappedSuperclass