在C＃中的通用变量中动态注入类型

Question

假设我有如下字典。

Dictionary<string, Expression> expressions = new Dictionary<string, Expression> { 
    { "Price", (Expression<Func<Phone, double>>) (p => p.Price) },     
    { "Brand", (Expression<Func<Phone, string>>) (p => p.Name) }     
    };

使用实体框架，我可以获得如下所示的结果数据。

BdPhonesDbEntities db = new BdPhonesDbEntities();
IQueryable<Phone> phones = db.Phones.Where(search.GetExpression());

现在，根据用户的选择，我想按价格（两倍）或名称（字符串）对结果进行排序。 使用固定类型（双精度）进行排序时，如下所示。

    Expression<Func<Phone, double>> keySelector =  
KeySelector<Func<Phone, double>>(expressions, search.OrderBy.PropertyName);            

现在，我想在“ double”位置动态插入类型，而不是仅针对double类型排序进行修复。 是否可以有条件地更改此代码的排序？

要一目了然地了解总代码，请检查以下图片或来自Gist

对该函数的调用如下所示：

Answer 1

试试这个实用工具类https://dotnetfiddle.net/T9CFYU

public static class Utility
{
    public static Expression<Func<TSource, object>> GetExpressionForProp<TSource>(this TSource source, string propertyName)
    {
        var param = Expression.Parameter(typeof(TSource), "x");
        Expression conversion = Expression.Convert(Expression.Property(param, propertyName), typeof(object));
        return Expression.Lambda<Func<TSource, object>>(conversion, param);
    }

    public static IOrderedQueryable<TSource> OrderByProp<TSource>(this IQueryable<TSource> source, string propertyName) 
        where TSource : class, new()
    {
        return source.OrderBy(new TSource().GetExpressionForProp(propertyName));

        //or comment where TSource : class, new() and
        //var param = Expression.Parameter(typeof(TSource), "x");
        //Expression conversion = Expression.Convert(Expression.Property(param, propertyName), typeof(object));
        //var shortExpression = Expression.Lambda<Func<TSource, object>>(conversion, param);
        //return source.OrderBy(shortExpression);
    }
}

一些用法，例如

List<Phone> orderedByPrice = null;
List<Phone> orderedByBrand = null;

/*Try: 1*/
orderedByPrice = Db.Phones.OrderBy(new Phone().GetExpressionForProp("Price")).ToList(); 
orderedByBrand = Db.Phones.OrderBy(new Phone().GetExpressionForProp("Brand")).ToList(); 

/*Try: 2*/
orderedByPrice = Db.Phones.OrderByProp("Price").ToList();
orderedByBrand = Db.Phones.OrderByProp("Brand").ToList();

/*Try: 3*/
var expressions = new Dictionary<string, Expression<Func<Phone, object>>>
{
    {"Price", (p => p.Price)},
    {"Brand", (p => p.Brand)}
};
orderedByPrice = Db.Phones.OrderBy(expressions["Price"]).ToList();
orderedByBrand = Db.Phones.OrderBy(expressions["Brand"]).ToList();