DDD - 聚合根 - 示例顺序和OrderLine [英] DDD - Aggregate Root - Example Order and OrderLine

问题描述

我试图让我的手肮脏学习DDD（通过开发一个例如电子商务网站，像订单， OrderLines ，产品，类别等）。
从我可以感知到的聚合根概念我认为订单类应该是 OrderLine 的聚合根

I am trying to get my hands dirty learning DDD (by developing a sample eCommerce site with entities like Order, OrderLines, Product, Categories etc). From what I could perceive about Aggregate Root concept I thought Order class should be an aggregate root for OrderLine.

到目前为止，事情进展顺利，但是当从UI定义创建订单流时，我感到困惑。
当我想在订单对象中添加订单行时，应该如何获取/创建一个 OrderLine 对象的实例：

Things went fine so far, however I am confused when it define a create order flow from UI. When I want to add an order line to my order object, how should I get/create an instance of an OrderLine object:

1. 我应该在我的UI / Service类中为 OrderLine（）语句进行硬编码
   
2. 我应该在订单中定义一个参数如 productID ，数量等参数 class？

1. Should I hardcode the new OrderLine() statement in my UI/Service class
2. Should I define a method with parameters like productID, quantity etc in Order class?

另外，如果要从UI或<$中删除硬编码的实例c $ c>订单使用DI的类。这是最好的方法？

Also, what if I want to remove the hardcoded instantiations from the UI or the Order class using a DI. What would be the best approach for this?

推荐答案

从我可以感知到的
总体根概念我认为订单
类应该是
OrderLine的aggreagrte根。

From what I could perceive about Aggregate Root concept I thought Order class should be an aggreagrte root for OrderLine.

是的，OrderLine的应该很可能在一个订单根目录下，因为OrderLine在父级订单之外可能没有任何意义。

Yes, OrderLine's should most likely be under an Order root, since OrderLine's likely make no sense outside of a parent Order.

我应该对新的OrderLine ）
语句在我的UI /服务类

Should I hardcode the new OrderLine() statement in my UI/Service class

可能不是，虽然这是它经常发生，工作。正如我所看到的，问题是，对象构造通常发生在不同的上下文中，验证约束根据上下文而有所不同。

Probably not, though this is how it happens often and it is made to work. The problem, as I see it, is that object construction often happens in different contexts, and the validation constraints differ depending on that context.

我应该在Order类中定义一个
参数的方法，如productID，数量等

Should I define a method with parameters like productID,quantity etc in Order class?

如下所示：

public OrderLine AddOrderLine(Product product, int Quantity ... )

这是一种方法。注意我使用了Product类而不是ProductId。有时一个比另一个更好。我发现我有很多因为各种原因 - 有时我有ID，没有什么好的理由来拉根，有时我需要另一个根来验证操作。

This is one way to do it. Notice I used a Product class instead of a ProductId. Sometimes one is preferable to the other. I find I use both a lot for various reasons - sometimes I have the ID and there's no good reason to pull the aggregate root, sometimes I need the other root to validate the operation.

另一种方法是为孩子们实现一个自定义集合。

Another way I do this is to implement a custom collection for the children.

所以我有：

order.OrderLines.Add(product, quantity);

这感觉有点自然或OO，特别是如果一个实体根有许多子集合避免混乱。

This feels a little more natural or OO, and in particular if an entity root has many child collections it avoids clutter.

order.AddOrderLine（）， order.AddXXX（）， order.AddYYY（）， order.AddZZZ（）

对

order.OrderLines.Add（）， order.ZZZs.Add（）， order.YYYs.Add（）

此外，如果我要从UI
或使用DI的Order类中删除
硬编码的实例。什么
将是最好的方法？

Also, what if I want to remove the hardcoded instantiations from the UI or the Order class using a DI. What would be the best approach for this?

这将是工厂模式的教科书案例。我将这样的工厂注入我的自定义集合，以支持 Add（）方法中的实例化。

This would be a textbook case for the Factory pattern. I inject such a Factory into my custom collections to support instantiation in those Add() methods.

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