Nhibernate 中具有复合 ID 的意外代理对象 [英] Unexpected proxy objects in Nhibernate with composite ID's

问题描述

我有一个使用复合 ID 的数据结构(我不想更改为单个)除了多对一连接(如果连接为空，而不是将属性映射到 null，而是将其映射到空代理对象)之外，一切都可以正常加载.我写了一个丑陋的工作(见下面).有什么解决办法吗?

I have a data structure which uses composite ids (Which I dont wish to change to single) Everything loads fine except for many-to-one joins which if the join is empty, instead of mapping the property to null, maps it to an empty proxy object. I have written an ugly work around( see bleow). Any solutions to this?

私有节点_Parent;

private Node _Parent;

    public Node Parent
    {
        get
        {
            return this._Parent;
        }
        set
        {
            this._Parent = Proxy.Check<Node>(value);
        }
    }
internal static class Proxy
{
    public static T Check<T>(T obj) where T : PersistentObject
    {
        if (obj is NHibernate.Proxy.INHibernateProxy && obj != null)
        {
            try 
            {
                int id = obj.ID;
                return obj;             
            }
            catch //Proxy only object cant retrieve ID
            {
                return null;
            }
        }
        else
        {
            return obj;
        }
    }

}

以映射文件开头

<class name="Node" table="Node">
    <composite-id>
        <key-property name="ID"/>
        <key-property name="VersionID"/>
    </composite-id>

和访问者

    <many-to-one name="Node" class="Node" >
        <column name="NodeID"/>
        <column name="VersionID" />
    </many-to-one>

推荐答案

不确定这是否是这种情况的完美解决方案，但是当我在使用旧数据库工作时遇到同样的问题时，这为我解决了这个问题复合键.

Not exactly sure if this is the perfect fix for this situation, but this fixed the issue for me when I encountered the same problem while working on an old DB with composite keys.

通过将 not-found 设置为忽略链接，NHibernate 会将空对象视为空对象而不是异常.当使用这种技术时，NHibernate 将执行一个单独的查询，所以可能会有小的性能影响，因为这基本上是急切加载对象.

By setting not-found to ignore on your links, NHibernate will treat empty objects as null instead of exceptions. When using this technique NHibernate will execute a seperate query so there may be small performance hits, as this is basically eager loading the object.

您可以尝试直接加载对象而不是使用这种技术，但我感觉它会返回一个异常，因为它期待一个对象(非空).如果这不起作用，我建议在 NHibernate 论坛上发布一个问题，因为我绝对不是这方面的专家，但这对您来说可能是一个较小/不那么丑陋的工作.

You could try just eager loading the object instead of using this technique, but I have a feeling it would return an exception as it would be expecting an object (not null). I would suggest posting a question in the NHibernate forums if this doesn't work as I am definately not an expert in this area, but this may be a smaller/less ugly work around for you.

例如:

<many-to-one name="Node" class="Node" not-found="ignore">
    <column name="NodeID"/>
    <column name="VersionID" />
</many-to-one>

希望这会有所帮助，

杰

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