提取功能来自Expression< [英] Extracting Func<> from Expression<>

问题描述

我想从以下表达式中提取Func<>:

I wanna extract the Func<> from the following Expression :

Expression<Func<IQueryable<Entity>, IOrderedQueryable<Entity>>> order = q => q.OrderByDescending(c=>c.FullName);

Func<IQueryable<Entity>, IOrderedQueryable<Entity>> orderFunc = ?

我该怎么办?

以及如何将 Func< IQueryable< Entity>，IOrderedQueryable< Entity> 转换为 Expression< Func< IQueryable< Entity>，IOrderedQueryable< Entity>></code>吗?

And how can we convert Func<IQueryable<Entity>, IOrderedQueryable<Entity>> to Expression<Func<IQueryable<Entity>, IOrderedQueryable<Entity>>> ?

推荐答案

您可以使用 Compile 方法将任何 Expression< TDelegate> 转换为 TDelegate.

You can use the Compile method to turn any Expresstion<TDelegate> into a TDelegate.

无法将委托转换为 Expression< TDelegate> .当表达式被编译为委托时，有关组成表达式的详细信息会丢失.

There is no way to convert a delegate into an Expression<TDelegate>. The detailed information about what makes up the expression was lost when it was compiled into a delegate.

从理论上讲，您可以通过执行类似的操作来创建一个表达式，该表达式的主体除了调用给定的委托人之外什么都不做:

You could, in theory create an expression who's body does nothing but invoke the given delegate, by doing something like this:

Func<int> function = () => 42;
Expression<Func<int>> expression = () => function();

，但是这样的表达并没有真正的用处.该表达式内部确实没有任何有意义的信息.因此，尽管在技术上可行，但从未真正实用.

but such an expression isn't really useful. There really isn't any meaningful information inside of that expression. So while it's technically possible, it's never really practical.

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