Question

我正在使用弹簧休息创建一个休眠的Web应用程序，我被困在两个表之间。我想将表列与另一个表列映射。我已经在jsp中完成了它，但现在我想在hibernate中完成它。我从alert表中获取author_id，然后我想从user_table获取该作者id的个人资料照片。

Jsp代码：

<%

String sql = "select author_id from alert where id=2";
Statement st = con.createStatement();
ResultSet rs = st.executeQuery(sql);
while(rs.next()){
String aid = rs.getString("author_id");
String sql1 = "select profile_img from user_table where id='"+aid+"'";
Statement st1 = con.createStatement();
ResultSet rs1 = st1.executeQuery(sql1);
while(rs1.next()){
String image_name = rs1.getString("profile_img");
}
}
%>

我想在hibernate中这样做。这是我的Alert类

@Entity
@Table(name="alert")
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class Alert implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
@Column(name="id")
private long id;

@Column(name="author_id")
private long author_id;

public long getId() {
    return id;
}
public void setId(long id) {
    this.id = id;
}

public long getAuthor_id() {
    return author_id;
}

public void setAuthor_id(long author_id) {
    this.author_id = author_id;
}

这是我的用户类

@Entity
@Table(name="user_table")
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
@Column(name="id")
private long id;

@Column(name="profile_img")
private String img_name;

public long getId() {
    return id;
}

public void setId(long id) {
    this.id = id;
}

public String getImg_name() {
    return img_name;
}

public void setImg_name(String img_name) {
    this.img_name = img_name;
}
}

这是我的DAO课程：

@Autowired
SessionFactory sessionFactory;

Session session = null;
Transaction tx = null;

public User getUserById(long id) throws Exception {
    session = sessionFactory.openSession();
    User user = (User) session.load(User.class, new Long(id));
    tx = session.getTransaction();
    session.beginTransaction();
    tx.commit();
    return user;
}

@SuppressWarnings({ "unchecked", "rawtypes" })
public List<Alert> getAlertById(long id) throws Exception {
    session = sessionFactory.openSession();
    Criteria cr = session.createCriteria(Alert.class);
    cr.add(Restrictions.eq("alert_viewer_id", id));
    List alert = cr.list();
    tx = session.getTransaction();
    session.beginTransaction();
    tx.commit();
    return alert;
}

请帮助我，我陷入了休眠状态。

Answer 1

当您使用ORM时，您需要考虑对象及其相互之间的关系，而不是数据库表，列，外键等。虽然您可以将表和列直接映射到类和字段，但是因为将应用程序数据视为对象图并使用ORM管理该图的真正目的将被打败，所以这样做不会有太多的里程。

如果你改变：

@Column(name="author_id")
private long author_id;

public long getAuthor_id() { return author_id; }

public void setAuthor_id(long author_id) { this.author_id = author_id; }

为：

@JoinColumn(name = "author_id")
@ManyToOne(fetch = FetchType.LAZY)
private User author;

public User getAuthor() { return author; }

public void setAuthor(User author) { this.author = author; }

只要您有Alert个对象，只需在其上调用getAuthor即可获得可以直接使用的User对象。

此更改不需要对数据库进行任何更改。

如何在hibernate中将表列与另一个表列映射

1 个答案: