Hibernate注解联合主键 如何使用

解答：Hibernate的注解方式可以用来定义联合主键，使用@Embeddable和@EmbeddedId注解。

一、@Embeddable和@EmbeddedId注解

在Hibernate注解中，使用@Embeddable注解的类中可以嵌入其他属性，而这些属性可以被@EmbeddedId注解的类所使用。@Embeddable注解的类中的getter和setter方法可以直接被使用@EmbeddedId注解的类所访问和修改。

示例代码：

@Embeddable
public class UserId implements Serializable {

    private String firstName;

    private String lastName;

    public UserId() {}

    public String getFirstName() { return firstName; }
    public void setFirstName(String firstName) { this.firstName = firstName; }

    public String getLastName() { return lastName; }
    public void setLastName(String lastName) { this.lastName = lastName; }
}

@Entity
public class User {

    @EmbeddedId
    private UserId id;

    private String email;
    private String password;

    // getters and setters ...

}

二、自定义主键生成策略

在@EmbeddedId注解的类中，可以自定义主键生成策略，支持的策略包括IDENTITY、SEQUENCE、TABLE、AUTO、NONE等。在@Id注解中也可以定义主键生成策略。

示例代码：

@Entity
@IdClass(CompositePrimaryKey.class)
public class User {

    @Id
    private String firstName;

    @Id
    private String lastName;

    private String email;
    private String password;

    // getters and setters ...
}

public class CompositePrimaryKey implements Serializable {

    private String firstName;
    private String lastName;

    public CompositePrimaryKey() {}

    public CompositePrimaryKey(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    // getters and setters ...
}

@Entity
@TableGenerator(
    name = "user_gen",
    table = "id_gen",
    pkColumnName = "gen_name",
    valueColumnName = "gen_val",
    allocationSize = 100
)
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "user_gen")
    private long id;

    @EmbeddedId
    private UserIdentity userIdentity;

    // other fields
}

三、复合主键的继承关系

在复合主键的继承关系中，子类需要重新定义父类的主键属性，并在@EmbeddedId注解中定义子类的主键属性。

示例代码：

@Entity
public class Vehicle {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    @Embedded
    private VehicleRegistration registration;

    // getters and setters ...
}

@Embeddable
public class VehicleRegistration {

    private String registrationNumber;
    private String registrationCountry;

    // getters and setters ...
}

@Entity
@AttributeOverrides({
    @AttributeOverride(name = "registrationNumber", column = @Column(name = "bike_reg_no")),
    @AttributeOverride(name = "registrationCountry", column = @Column(name = "bike_reg_country"))
})
public class Bike extends Vehicle {

    @EmbeddedId
    private VehicleRegistration registration;

    // getters and setters ...
}

@Entity
@AttributeOverrides({
    @AttributeOverride(name = "registrationNumber", column = @Column(name = "car_reg_no")),
    @AttributeOverride(name = "registrationCountry", column = @Column(name = "car_reg_country"))
})
public class Car extends Vehicle {

    @EmbeddedId
    private VehicleRegistration registration;

    // getters and setters ...
}

以上就是关于Hibernate注解联合主键的详细阐述，其中包括了@Embeddable和@EmbeddedId注解、自定义主键生成策略以及复合主键的继承关系。掌握了这些知识，您将能够更好地使用Hibernate注解方式定义联合主键。