NHibernate QueryOver别名问题 [英] NHibernate QueryOver Alias Issue

问题描述

我正在Visual Web Developer 2010 Express的.Net 4目标项目中使用NuGet的最新版本NHibernate(3.3.1.4000).

I'm using the latest version of NHibernate (3.3.1.4000) from NuGet in .Net 4 targeted project in Visual Web Developer 2010 Express.

当我尝试遵循我看到的用于定义别名的示例时，使用lambda设置它们时会出现异常(请参见屏幕截图).

When I attempt to follow examples I've seen for defining aliases, I get an exception when setting them up using lambdas (see screenshot).

如您所见，我收到错误Cannot convert lambda expression to type 'string' because it is not a delegate type.

As you can see I'm getting the error Cannot convert lambda expression to type 'string' because it is not a delegate type.

我在代码顶部引用了LINQ命名空间:

I have references to the LINQ namespaces in the top of my code:

using System.Linq;
using System.Linq.Expressions;

对可能导致问题的原因有什么想法?

Any thoughts on what might be causing the problem?

推荐答案

要在表达式中使用像role这样的变量，就必须像这样先定义它...

In order to use a variable like role in an expression, you have to define it first, like so...

Role roleAlias = null; // <-- these two lines are missing from your code.
Person personAlias = null; 

var x = session.QueryOver<Role>(() => roleAlias)
    .JoinAlias(r => r.People, () => personAlias)
    // ...

ISession.QueryOver<T>(...)具有四个重载:

• .QueryOver<T>()
• .QueryOver<T>(Expression<Func<T>> alias)
• .QueryOver<T>(string entityName)
• .QueryOver<T>(string entityName, Expression<Func<T>> alias)

• .QueryOver<T>()
• .QueryOver<T>(Expression<Func<T>> alias)
• .QueryOver<T>(string entityName)
• .QueryOver<T>(string entityName, Expression<Func<T>> alias)

显然，因为它无法弄清role是什么，所以假设您正在尝试使用.QueryOver<T>(string entityName)重载，因此出现了无法转换...键入'字符串'"错误消息.

Apparently because it can't figure out what role is, it's assuming you're trying to use the .QueryOver<T>(string entityName) overload, hence the "Cannot convert ... to type 'string'" error message.

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