Question

我要为GroupBy构建一个动态表达式树。我想要实现的就是这样。

var NestedGrouped = listOfPerson.GroupByMany(x => x.Name,x=>x.Age).ToList();

我的人员类如： -

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;
        }
    }

对于单个属性我能够构建表达式，但我想做GROUPBY 具有多个列，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 =＆gt; x.Name，x =＆gt; x.Age））。
请帮忙。在此先感谢。

Answer 1

GroupByMany()接受委托数组，每个密钥一个委托。因此，您需要为每个键创建和编译单独的表达式。

代码看起来像：

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());
}

构建具有多个属性的动态GroupBy选择器表达式树

1 个答案: