构建具有多个属性的动态组选择器表达式树 [英] Building Dynamic GroupBy Selector Expression Tree With Multiple Properties

问题描述

我要为GroupBy构建动态表达式树。我想要实现的就是这样。

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

我的人员类别如下： -

  class Person 
 {
 public string Name {get;组; } 
 public int Age {get;组; } 
 public float Salary {get;组; } 
} 
 public class GroupResult 
 {
 public object Key {get;组; } 
 public int Count {get;组; } 
 public IEnumerable Items {get;组; } 
 public IEnumerable< GroupResult>子组{get;组; } 
 public override string ToString（）
 {return string.Format（{0}（{1}），Key，Count）; } 
} 
 public static class MyEnumerableExtensions 
 {
 public static IEnumerable< GroupResult> GroupByMany< TElement>（
这个IEnumerable< TElement>元素，
 params Func< TElement，object> [] groupSelectors）
 {
 if（groupSelectors.Length> 0）
 {
 var selector = groupSelectors.First（）; 
 
 //递归减少列表直到零
 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 
返回null; 
} 
} 
  

对于单个属性我可以构建表达式我想做GROUPBY
与多个列，如上所示。
FOR SINGLE PROPERTY： -

  ParameterExpression parameter = Expression.Parameter（typeof（Person），lambdaKey）; 
 var menuProperty = Expression.PropertyOrField（parameter，Name）; 
 var lambda = Expression.Lambda  var selector = lambda.Compile（）; 
 var result = P1.GroupByMany（selector）; // P1是PERSON的列表
  

如何在表达式树中添加多个列（例如（x => x.Name，x => x.Age））。

请帮助。感谢Advance。

解决方案

GroupByMany（）接受代理数组，每个密钥的一个代表。因此，您需要的是为每个键创建和编译一个单独的表达式。

代码可能如下所示：

  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>（
此IEnumerable< TElement>元素，
 params string [] groupKeys）
 {
返回元素.GroupByMany（groupKeys.Select（CreateSelector< TElement>））。 ToArray的（））; 
} 
  

I am to build a dynamic Expression Tree for GroupBy. All i want to achieve is like this.

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

My Person Class is like :-

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;
        }
    }

For Single Property I am able to build the expression but i want to do GROUPBY with multiple columns as shown above. FOR SINGLE PROPERTY :-

 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

How to ADD multiple columns in Expression Tree (e.g (x => x.Name,x=>x.Age)).
Please Help. Thanks in Advance.

解决方案

GroupByMany() accepts array of delegates, one delegate for each key. So, what you need is to create and compile a separate expression for each key.

The code could look something like:

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());
}

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