C# linq查询之动态OrderBy用法实例

本文实例讲述了C# linq查询之动态OrderBy用法。分享给大家供大家参考。具体分析如下：

groupList是原始数据集合，List<T>

sortOrder是排序类型，desc 或者asc

sortName是排序属性名称

1.使用反射。

private static object GetPropertyValue(object obj, string property)
{
 System.Reflection.PropertyInfo propertyInfo = obj.GetType().GetProperty(property);
 return propertyInfo.GetValue(obj, null);
}
var resultList = sortOrder == "desc" ? groupList.OrderByDescending(p => GetPropertyValue(p, sortName)) : groupList.OrderBy(p => GetPropertyValue(p, sortName));
//linq方式：
//
var resultList1 = from p in groupList orderby GetPropertyValue(p, m.SortName) select p;
if (sortOrder == "desc")
resultList1 = from p in groupList orderby GetPropertyValue(p, sortName) descending select p;

2.调用AsQueryable()

将泛型 System.Collections.Generic.IEnumerable<T> 转换为泛型 System.Linq.IQueryable<T>。

var groupQueryList = groupList.AsQueryable();//here
var tmpList = groupQueryList.OrderBy(sortName, sortOrder);

需要如下扩展方法：

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;
}

希望本文所述对大家的C#程序设计有所帮助。