具有多个相同类型的值对象的聚合根问题

Question

我是 Spring Data JDBC 的新手，我使用 Spring-Boot 2.5.0、Java 11 和 Lombok（简化的代码示例）创建了一个包含两个 Address 值的 Customer 聚合。

我有一个客户实体（聚合根）和一个地址值对象

@Data
@Builder
@AllArgsConstructor
class Customer {
    @Id Long id;
    String name;
    Address address1;
    Address address2;
}

@Data
@Builder
@AllArgsConstructor
class Address {
    String city;
}

和一个客户实体的存储库

@Repository
public interface CustomeRepository extends CrudRepository<Customer, Long> {
}

使用 Postgres 的 db 架构如下所示

CREATE TABLE "customer" (
  "id"                  BIGSERIAL       NOT NULL,
  "name"                VARCHAR(255)    NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE "address" (
  "id"                  BIGSERIAL       NOT NULL,
  "customer"            BIGINT,
  "city"                VARCHAR(255)    NOT NULL,
  PRIMARY KEY (id)
);

创建和存储客户

        var address1 = Address.builder().city("New York").build();
        var address2 = Address.builder().city("Chicago").build();
        var customer = Customer.builder().name("Joe").address1(address1).address2(address2).build();
        var result = customerRegistry.save(customer);

到目前为止一切都很好，数据库中的条目看起来也很好

 id | name 
----+------
  1 | Joe


 id | customer |   city   
----+----------+----------
  1 |        1 | Chicago
  2 |        1 | New York

所以期待一位客户，但这样做时

var customers = customerService.findAll();
customers.forEach(c -> log.debug("Customer: {}", c));

输出将是

Customer(id=1, name=Joe, address1=Address(city=New York), address2=Address(city=Chicago))
Customer(id=1, name=Joe, address1=Address(city=Chicago), address2=Address(city=Chicago))
Customer(id=1, name=Joe, address1=Address(city=New York), address2=Address(city=New York))
Customer(id=1, name=Joe, address1=Address(city=Chicago), address2=Address(city=New York))

然后这样做

var customer = customerRepository.getById(result.getId());

会导致

org.springframework.dao.IncorrectResultSizeDataAccessException: Incorrect result size: expected 1, actual 4

顺便说一句。如果客户只有一个地址字段，一切都会按预期进行。

所以我错过了什么还是这是一个错误？

Answer 1

您可以将@Column 注释放在一个或两个属性上，指定用于反向引用Customer 的不同列。

例如：

class Customer {
    @Id Long id;
    String name;
    @Column("first")
    Address address1;
    @Column("second")
    Address address2;
}

期望以下address 表

CREATE TABLE "address" (
  "id"                  BIGSERIAL       NOT NULL,
  "first"               BIGINT,
  "second"              BIGINT,
  "city"                VARCHAR(255)    NOT NULL,
  PRIMARY KEY (id)
);

如需了解更多背景信息和超出当前特定问题的其他替代方案，请参阅Why is a entity - value relationship implemented as a back reference in Spring Data JDBC