io.github.dddplus.model.association

接口 HasMany<Entity>

类型参数:

Entity - 被关联对象类型

所有超级接口:

IBag

public interface HasMany<Entity>
extends IBag

关联对象：1对多.

Learned from 《Analysis Patterns》14.1.2 Interface for Associations：The interface for associations in an OO language is a series of operations to access and update the association.

关联对象用于处理实体之间的生命周期边界，生命周期边界是指相关联的对象是否同时出现/消失在内存中.

对象关系，有2种：(聚合关系，引用关系)，前者通过IAggregateRoot实现；后者通过关联对象实现，从而避免逻辑泄露.

设计上是把关联关系设计成对象(接口).

有了关联对象，就去掉了与(数据库，外部服务)等外部依赖的强关联.

      the association object: interface/pointer
             ^
             │
     user.orders().list()
                     │
                     V
           load into memory from somewhere(db/remote api/etc)
 

Example:

 

 ℗lombok.Getter(AccessLevel.PACKAGE)
 public class Task implements IAggregateRoot {
     public interface Orders extends HasMany<Order> {
         List<Order> pendingOrders();
     }

     ℗lombok.experimental.Delegate
     private Orders orders; // task.pendingOrders()
 }
 public class Order implements IAggregateRoot {}

 // 在infrastructure层实现
 public TaskOrders implements Task.Orders {
     private final String taskNo;
     private Dao dao;
     public TaskOrders(String taskNo) {
         this.taskNo = taskNo;
     }

     public List<Order> pendingOrders() {
         return dao.findPendingOrdersByTask(taskNo);
     }
 }

 // mybatis/mapper.xml
 <resultMap id="taskOrders" type="io.github.design.mybatis.associations.TaskOrders">
     <result column="task_no" property="taskNo" javaType="String"/>
 </resultMap>
 <resultMap id="checkTask" type="io.github.design.CheckTask">
     <id column="id" property="id" jdbcType="BIGINT"/>
     <association property="orders" resultMap="taskOrders"/>
 </resultMap>