Question

我有三个实体：

客户
它的复合PK为...... customer_id和company_id

数据
ID：data_id
FK：area_id（来自下面的区域）
FK：customer_id（来自上方客户）

区域
ID：area_id
FK：company_id（来自上面的客户）

如何在JPA中创建@Join注释？我假设我必须使用@JoinTable，但我不知道该怎么做。

客户

@Entity
@Table(name="customer")
@NamedQuery(name="Customer.findAll", query="SELECT c FROM Customer c")
public class Customer implements Serializable {
    private static final long serialVersionUID = 1L;

    @EmbeddedId
    private CustomerPK id;

    //bi-directional many-to-one association to CustomColumnDataCustomer
    @OneToMany(mappedBy="customer")
    private List<CustomColumnDataCustomer> customColumnDataCustomers;

CustomerPK

@Embeddable
public class CustomerPK implements Serializable {
    //default serial version id, required for serializable classes.
    private static final long serialVersionUID = 1L;

    @Column(name="customer_id")
    private long customerId;

    @Column(name="company_id")
    private String companyId;

CustomColumnDataCustomer

@Entity
@Table(name="custom_column_data_customer")
@NamedQuery(name="CustomColumnDataCustomer.findAll", query="SELECT c FROM     CustomColumnDataCustomer c")
public class CustomColumnDataCustomer implements Serializable {
private static final long serialVersionUID = 1L;

    @Id
    @Column(name="custom_column_data_cust_uid")
    private int customColumnDataCustUid;

    //bi-directional many-to-one association to Customer
    @ManyToOne
    private Customer customer;

    //bi-directional many-to-one association to AreaXCustomColumn
    @ManyToOne
    @JoinColumn(name="area_x_custom_column_uid")
    private AreaXCustomColumn areaXCustomColumn;

AreaXCustomColumn

@Entity
@Table(name="area_x_custom_column")
@NamedQuery(name="AreaXCustomColumn.findAll", query="SELECT a FROM AreaXCustomColumn a")
public class AreaXCustomColumn implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @Column(name="area_x_custom_column_uid")
    private int areaXCustomColumnUid;

    @Column(name="company_id")
    private String companyId;

    //bi-directional many-to-one association to CustomColumnDataCustomer
    @OneToMany(mappedBy="areaXCustomColumn")
    private List<CustomColumnDataCustomer> customColumnDataCustomers;

    //bi-directional many-to-one association to CustomColumnDefinition
    @ManyToOne
    @JoinColumn(name="custom_column_definition_uid")
    private CustomColumnDefinition customColumnDefinition;

Answer 1

解决此问题的方法是使用注释@EmbeddedId和@JoinColumn。

我最近在一个项目上需要一个类似的解决方案。我认为如果我通过例子解释它会更容易：

我有三个对象，Platform，EventMaster和Membership。

在这种情况下，Membership是您的客户，它有两个PK，即平台ID和EventMaster ID（由@EmbeddedID解决）：
```
@EmbeddedId
private MembershipKey id;
```

MembershipKey类只包含另一个类的PK：

@ManyToOne
@JoinColumn(name = "eventmaster_id")
private EventMaster eventMaster;

@ManyToOne
@JoinColumn(name = "mosplatform_id")
private MOSPlatform platform;

Platform和EventMaster类看起来都一样（这是Platform类）：

@OneToMany(mappedBy = "id.platform")
private List<Membership> memberships;

我认为这可以帮助您制定解决方案。

编辑：问题中的代码已编辑。

JPA - 加入三张桌子。一个PK。另外两个都有PK的一部分

1 个答案: