级联删除使用单向多对多映射 [英] Cascade on delete using unidirectional Many-To-Many mapping

问题描述

我使用Fluent和NHibernate。
我有两个对象说A& B之间有多对多的关系。
当HasMany B使用单向多对多映射时。在B中没有关于A（单向）的引用。

这在数据库中创建了第三个表（名为ABMapping），它具有与A的主键相关的两列&安培; B。

如果删除对象A，则删除与AB相关的ABMapping表中的条目。这很酷。

但是，现在我不能删除一个对象B，因为它有一个FK约束。我该如何设置它，以便在删除B时，自动删除AB映射中与B有关的所有条目？如果B不引用A，那么它不知道映射表，所以它不能级联删除。正如我所看到的，您有两种选择：

1. 使用FK或触发器上的级联删除级联数据库中的删除。
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2. 将关系从B映射到A;您不必将其暴露给您的班级的消费者，则可以使用访问策略将A集合映射为专用字段。我总是这样做的集合（使用.Access.CamelCaseField（前缀.Underscore）），所以我不公开IList。
   

I am using Fluent and NHibernate. I have two objects say A & B which has a many-to-many relationship between them. I am using a unidirectional many-to-many mapping when A HasMany B's. There is no reference in B about A (Unidirectional).

This creates a third table (named ABMapping) in the Database which has the two columns relating to primary keys of A & B.

If I delete the object A, the entries from the ABMapping table related to A are deleted. That's cool.

But, now I am not able to delete an object B, as it has a FK constraint. How can I set it up so that on deleting B, all entries related to B in ABMapping are deleted automatically?

解决方案

If B doesn't reference A then it doesn't know about the mapping table so it can't cascade the delete. As I see it you have two options:

1. Cascade the delete in the database using cascading deletes on your FK or a trigger.
2. Map the relationship from B to A; you don't have to expose it to consumers of your class, the A collection could be mapped as a private field using an access strategy. I always do this for collections (using .Access.CamelCaseField(Prefix.Underscore)) so that I don't expose IList.

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