学步园

支持 info.A.B.C 这样的排序表达式

    /// <summary>
/// 在 linq 查询中使用字符串表达式进行排序
/// </summary>
    public static class OrderByStringExpressionExtensions
    {
public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
        {
return ApplyOrder<T>(source, property, "OrderBy");
        }
public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
        {
return ApplyOrder<T>(source, property, "OrderByDescending");
        }

public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
        {
return ApplyOrder<T>(source, property, "ThenBy");
        }
public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
        {
return ApplyOrder<T>(source, property, "ThenByDescending");
        }

static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName)
        {
string[] props = property.Split('.');
            Type type = typeof(T);
            ParameterExpression arg = Expression.Parameter(type, "x");
            Expression expr = arg;

foreach (string prop in props)
            {
// use reflection (not ComponentModel) to mirror LINQ  
                PropertyInfo pi = type.GetProperty(prop);
                expr = Expression.Property(expr, pi);
                type = pi.PropertyType;
            }
            Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
            LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);
object result = typeof(Queryable).GetMethods().Single(
                    method => method.Name == methodName
&& method.IsGenericMethodDefinition
&& method.GetGenericArguments().Length == 2
&& method.GetParameters().Length == 2)
                .MakeGenericMethod(typeof(T), type)
                .Invoke(null, new object[] { source, lambda });
return (IOrderedQueryable<T>)result;
        }
    }