实体框架 - 清除子集 [英] Entity Framework - Clear a Child Collection

问题描述

我遇到了一个有趣的问题，实体框架，并基于我不得不用来解决它的代码，我怀疑我的解决方案不太理想。表A和表B之间有一对多关系，表B中的实体参考了表A。我有一个场景，我想同时删除TableA中的所有孩子，我认为这可以通过简单地清除集合来实现：

I have run into an interesting problem with Entity Framework and based on the code I had to use to tackle it I suspect my solution is less than ideal. I have a 1-to-Many relationship between Table A and Table B where entities in TableB have a reference to TableA. I have a scenario where I want to simultaneously delete all children of a row in TableA and I thought this could be achieve by simply clearing the collection:

Entity.Children.Clear()

不幸的是，当我尝试保存更改时作为外键违规。

Unfortunately, when I attempted to save changes this produced as a Foreign Key violation.

正在添加关系或
从AssociationSet
'FK_EntityB_EntityA'中删除。使用基数
约束，还必须添加或删除相应的EntityB
。

A relationship is being added or deleted from an AssociationSet 'FK_EntityB_EntityA'. With cardinality constraints, a corresponding 'EntityB' must also be added or deleted.

解决方案想出来的是通过实体上下文的DeleteObject（）手动删除对象，但是我只是知道我使用的这个逻辑一定是错误的。

The solution I came up with was to manually delete object via the entity context's DeleteObject(), but I just know this logic I am using has got to be wrong.

while (collection.Any())
    Entities.DeleteObject(collection.First());

对于一个，我不得不使用Where（）循环的事实远远不及理想，但我认为这纯粹是我的语义评估。在任何情况下，我正在做这些事情是否有问题，或者是否有更好的方法来清除实体的子实体集合，以便Entity Framework在所有被删除的对象上正确地调用数据存储删除？ p>

For one, the fact that I had to use a Where() loop seems far less than ideal, but I suppose that's purely a semantic assessment on my part. In any case, is there something wrong with how I am doing this, or is there perhaps a better way to clear a child entity collection of an entity such that Entity Framework properly calls a data store delete on all of the removed objects?

推荐答案

Clear（）删除引用实体，而不是实体本身。

Clear() removes the reference to the entity, not the entity itself.

如果您打算这样执行相同的操作，您可以处理 AssociationChanged ：

If you intend this to be always the same operation, you could handle AssociationChanged:

Entity.Children.AssociationChanged += 
    new CollectionChangeEventHandler(EntityChildrenChanged);
Entity.Children.Clear();            

    private void EntityChildrenChanged(object sender,
        CollectionChangeEventArgs e)
    {
        // Check for a related reference being removed. 
        if (e.Action == CollectionChangeAction.Remove)
        {
            Context.DeleteObject(e.Element);
        }
    }

您可以使用部分课程。

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