linq 扩展，在查询中使用字符串表达式对结果进行排序

最新推荐文章于 2024-04-30 13:16:51 发布

转载最新推荐文章于 2024-04-30 13:16:51 发布 · 119 阅读

0 ·

CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/illusion/archive/2011/04/14/2016369.html

本文介绍了一个Linq查询的扩展方法，通过这些方法可以在Linq查询中使用字符串表达式来实现排序操作，包括正序、倒序及次级排序等。

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;
}
}

转载于:https://www.cnblogs.com/illusion/archive/2011/04/14/2016369.html