為LINQ / Lambda創建一個OrderBy表達式

Question

我正在創建一個概念證明，它將Lambda / LINQ用於動態where和orderby。 以下代碼適用於where表達式，但我無法弄清楚如何通過表達式創建訂單。 對於這個例子，如果可能的話我想保持簡單; 我寧願不編寫修改表達式樹的代碼。

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();
}

我想要的是類似於以下內容，但無法弄清楚通過表達式創建順序的代碼。

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();
}

如果您想知道，我正在使用LinqPad進行此概念驗證。

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擴展方法，它接受一個Expression<Func<T, TOrderBy>>因為該表達式可以導致任何類型的依賴

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

因此，您的包裝器方法需要能夠接受傳入的泛型類型。

Answer 2

你在尋找的是：

Expression<Func<Products, dynamic>>;

嘗試創建一個結構/類來保存Expression，如果它是升序或降序。