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。