为LINQ/Lambda创建一个order表达式

Question

我正在创建一个使用Lambda/LINQ进行动态位置和顺序的概念证明。下面的代码适用于where表达式，但我不知道如何创建按表达式排序。对于这个例子，如果可能的话，我想保持简单;我宁愿不编写修改表达式树的代码。

void Main()
{
    DateTime productSince = DateTime.UtcNow.Subtract(new TimeSpan(1,30,0));
    Expression<Func<Products, bool>> filter = d => d.CreatedDate > productSince && d.Price < 100 ;    
    List<Products> products = GetProducts(filter, Products);
    Console.WriteLine(products);
}
private static List<Products> GetProducts(Expression<Func<Products, bool>> filter,  Table<Products> Products)
{
    var products = Products.Where(filter);
    return products.ToList();
}

我想要的是类似于下面的代码，但不知道如何创建按表达式排序的代码

void Main()
{
    DateTime productSince = DateTime.UtcNow.Subtract(new TimeSpan(1,30,0));
    Expression<Func<Products, bool>> filter = d => d.CreatedDate > productSince && d.Price < 100 ;
    Expression<Func<Products, ????>> orderBy = d => ??????;
    List<Products> products = GetProducts(filter, orderBy, Products);
    Console.WriteLine(products);
}
private static List<Products> GetProducts(Expression<Func<Products, bool>> filter,
               Expression<Func<Products, ???>> orderBy, Table<Products> Products)
{
    var products = Products.Where(filter).OrderBy(orderBy);
    return products.ToList();
}

如果你想知道，我正在使用LinqPad来验证这个概念。

Answer 1

private static List<Products> GetProducts<TOrderBy>(Expression<Func<Products, bool>> filter,
               Expression<Func<Products, TOrderBy>> orderBy, Table<Products> Products)
{
    var products = Products.Where(filter).OrderBy(orderBy);
    return products.ToList();
}

如果你看一下OrderBy扩展方法它接受一个Expression<Func<T, TOrderBy>>因为表达式可以产生任何类型取决于

.OrderBy(x => x.ID) // <T, int>
.OrderBy(x => x.Name) // <T, string>

因此，您的包装器方法需要能够接受传入的泛型类型

Answer 2

你要找的是:

Expression<Func<Products, dynamic>>;

尝试创建一个结构/类来保存表达式，如果它是升序或降序。