Question

我要做的是根据用户ID将表连接到另一个表。

我有一个用户表和一个警报历史记录表，该表具有与用户ID相关联的外键。

我使用的是Netbeans 7.4生成的实体。

用户：

    @Entity
@Table(name = "Users", schema = "dbo")
public class User extends Model implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "UserID")
    private Integer userID;
            @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy = "userId")
            private Collection<AlertHistory> alertHistoryCollection;
     { ... }

提醒记录：

    @Entity
@Table(name = "Alert_History", schema = "dbo")
public class AlertHistory extends Model implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id")
    private Long id;
    @Basic(optional = false)
    @Column(name = "user_id")
    @ManyToOne(fetch = FetchType.EAGER)
    private int userId;
    @Basic(optional = false)
    @Column(name = "message_id")
    private long messageId;
    @Basic(optional = false)
    @Lob
    @Column(name = "alerts_triggered")
    private String alertsTriggered;
            {...}

我期望的是，当我加载用户时，它将尝试根据userId加入AlertsHistory表结果。但是，在运行时，AlertsHistory集合始终为null

更新：已解决

我看错了方法。为了进行JOIN，AlertHistory期望被传递给User对象，而不仅仅是userId键。将User字段添加到AlertHistory模型，并将@OneToMany(mappedBy = "userId")更改为@OneToMany(mappedBy = "user"，然后将@JoinColumn(name="user_id", referencedColumnName="userId") private User user;添加到User字段中AlertHistory 1}}让我整理出来！感谢大家的帮助。

Answer 1

首先，没有人想要null个集合，所以在User中执行此操作：

private Collection<AlertHistory> alertHistoryCollection = new ArrayList<>();
//assuming Java 7

然后您需要User中的AlertHistory个实例，如下所示：

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "UserID")
private User user;

玩框架加入表

1 个答案: