具有多个相同类型的值对象的聚合根问题 [英] Problem with aggregate root with more than one value object of the same type

问题描述

我是 Spring Data JDBC 的新手，并使用 Spring-Boot 2.5.0、Java 11 和 Lombok(代码示例简化)创建了一个具有两个地址值的 Customer 聚合.

I'm new to Spring Data JDBC and create a Customer aggregate with two Address values using Spring-Boot 2.5.0, Java 11 and Lombok (code examples simplified).

我有一个 Customer 实体(聚合根)和一个 Address 值对象

I have one Customer entity (aggregate root) and one Address value object

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

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

和 Customer 实体的一个 Repository

and one Repository for the Customer entity

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

使用 Postgres 的数据库架构看起来像这样

Using Postgres the db schema looks like this

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);

到目前为止一切顺利，数据库中的条目也很好

So far so good, also the entries in the database looking fine

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


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

所以期待一位客户，但在这样做时

So expecting one Customer, but when doing this

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))

并这样做

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

将导致

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，则一切都按预期工作.

Btw. If the Customer has only one address field everything works as expected.

所以我错过了什么还是这是一个错误?

So do I miss something or is this a bug?

推荐答案

您可以在一个或两个属性上添加 @Column 批注，指定不同的列以用于对 客户.

You can put a @Column annotation on one or both attributes, specifying different columns to use for the back-reference to Customer.

例如:

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

需要以下 address 表

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

有关超出手头特定问题的更多背景和其他替代方案，请参阅为什么实体 - 值关系实现为Spring Data JDBC 中的反向引用

For more background and other alternatives that go beyond the specific problem at hand see Why is a entity - value relationship implemented as a back reference in Spring Data JDBC

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