如何将表达式<Func<T,DateTime>>强制转换为表达式<Func<T,object>>

你不能只是在他们之间转换,因为他们不是同一种东西。但是,您可以在表达式树中有效地添加转换:

using System;
using System.Linq.Expressions;

class Test
{
    // This is the method you want, I think
    static Expression<Func<TInput,object>> AddBox<TInput, TOutput>
        (Expression<Func<TInput, TOutput>> expression)
    {
        // Add the boxing operation, but get a weakly typed expression
        Expression converted = Expression.Convert
             (expression.Body, typeof(object));
        // Use Expression.Lambda to get back to strong typing
        return Expression.Lambda<Func<TInput,object>>
             (converted, expression.Parameters);
    }

    // Just a simple demo
    static void Main()
    {
        Expression<Func<string, DateTime>> x = text => DateTime.Now;
        var y = AddBox(x);        
        object dt = y.Compile()("hi");
        Console.WriteLine(dt);
    }        
}

抢劫 和

x => Convert(x.PropertyName) ,但通常情况下 ASP.NETMVC 你想要这样的表达吗 x => x.PropertyName

Expression.Convert 是 某些情况下的表达式。

public static class LambdaExpressionExtensions
{
    public static Expression<Func<TInput, object>> ToUntypedPropertyExpression<TInput, TOutput> (this Expression<Func<TInput, TOutput>> expression)
    {
        var memberName = ((MemberExpression)expression.Body).Member.Name;

        var param = Expression.Parameter(typeof(TInput));
        var field = Expression.Property(param, memberName);
        return Expression.Lambda<Func<TInput, object>>(field, param);
    }
}

用法:

Expression<Func<T, DateTime>> expression = ...;
Expression<Func<T, object>> expr = expression.ToUntypedPropertyExpression();

public static Expression<Func<TModel, TToProperty>> Cast<TModel, TFromProperty, TToProperty>(Expression<Func<TModel, TFromProperty>> expression)
{
    Expression converted = Expression.Convert(expression.Body, typeof(TToProperty));

    return Expression.Lambda<Func<TModel, TToProperty>>(converted, expression.Parameters);
}

Expression<Func<string, object>> dateExp = text => DateTime.Now;
object dt = dateExp.Compile()("hi");
Console.WriteLine(dt);

Fiddle sample here