[英]Building Dynamic GroupBy Selector Expression Tree With Multiple Properties
我要为GroupBy构建动态的表达式树。 我想要实现的就是这样。
var NestedGrouped = listOfPerson.GroupByMany(x => x.Name,x=>x.Age).ToList();
我的人物课堂就像:-
class Person
{
public string Name{ get; set; }
public int Age{ get; set; }
public float Salary{ get; set; }
}
public class GroupResult
{
public object Key { get; set; }
public int Count { get; set; }
public IEnumerable Items { get; set; }
public IEnumerable<GroupResult> SubGroups { get; set; }
public override string ToString()
{ return string.Format("{0} ({1})", Key, Count); }
}
public static class MyEnumerableExtensions
{
public static IEnumerable<GroupResult> GroupByMany<TElement>(
this IEnumerable<TElement> elements,
params Func<TElement, object>[] groupSelectors)
{
if (groupSelectors.Length > 0)
{
var selector = groupSelectors.First();
//reduce the list recursively until zero
var nextSelectors = groupSelectors.Skip(1).ToArray();
return
elements.GroupBy(selector).Select(
g => new GroupResult
{
Key = g.Key,
Count = g.Count(),
Items = g,
SubGroups = g.GroupByMany(nextSelectors)
});
}
else
return null;
}
}
对于Single Property,我能够构建表达式,但我想对多列进行GROUPBY,如上所示。 对于单一财产:-
ParameterExpression parameter = Expression.Parameter(typeof(Person), "lambdaKey");
var menuProperty = Expression.PropertyOrField(parameter, "Name");
var lambda = Expression.Lambda<Func<Person, string>>(menuProperty, parameter);
var selector = lambda.Compile();
var result = P1.GroupByMany(selector);// P1 is list of PERSON
如何在表达式树中添加多个列(例如(x => x.Name,x => x.Age))。
请帮忙。 提前致谢。
GroupByMany()
接受一组委托,每个键一个委托。 因此,您需要为每个键创建并编译一个单独的表达式。
该代码可能类似于:
private static Func<TElement, object> CreateSelector<TElement>(string key)
{
var parameter = Expression.Parameter(typeof(TElement), "lambdaKey");
var property = Expression.PropertyOrField(parameter, key);
var lambda = Expression.Lambda<Func<TElement, string>>(property, parameter);
return lambda.Compile();
}
public static IEnumerable<GroupResult> GroupByMany<TElement>(
this IEnumerable<TElement> elements,
params string[] groupKeys)
{
return elements.GroupByMany(groupKeys.Select(CreateSelector<TElement>).ToArray());
}
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.