創建表達式<Func <IQueryable <T>，IOrderedQueryable <T> >>？

Question

我想創建一個Expression<Func<IQueryable<T>, IOrderedQueryable<T>>>，我有以下代碼：

Expression selector = q => q.RegistrationDate 

MethodInfo orderByMethodInfo = typeof(Queryable).GetMethods().First(method => method.Name == "OrderBy" && method.GetParameters().Count() == 2).MakeGenericMethod(argumentTypes); 
MethodInfo orderByDescMethodInfo = typeof(Queryable).GetMethods().First(method => method.Name == "OrderByDescending" && method.GetParameters().Count() == 2).MakeGenericMethod(argumentTypes); 

我要創建c => c.OrderBy(q => q.RegistrationDate)或c => c.OrderByDescending(q => q.RegistrationDate)或一般類似c => c.OrderByDescending(q => q.RegistrationDate).ThenBy(q=>q.Name)從上面的代碼。

請你指導我如何做到這一點？

Answer 1

var paramExpr = Expression.Parameter(typeof(IQueryable<T>)) 
var orderByExpr = Expression.Call(orderByMethodInfo, paramExpr, selector); 
var expr = Expression.Lambda<Func<IQueryable<T>, IOrderedQueryable<T>>>(orderByExpr, paramExpr); 

哪裏T是在你的selector表達RegistrationDate屬性的類型。

您可以使用MakeGenericType參數的類型得到查詢類型：

Type argType = typeof(DateTime); 
Type queryableType = typeof(IQueryable<>).MakeGenericType(argType);