C# linq查询之动态OrderBy用法实例
时间：2021-03-15 09:53:22|栏目：.NET代码|点击： 次
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。
