如何在LINQ採取（）方法中使用條件

Question

如何加入兩個表，並獲得基於B類變量的記錄值

Class A 
{ 
    RecordID int {get;set;} 

    Name string {get;set;} 
} 

Class B 
{ 
    Name string {get;set;} 

    DataToPick int {get;set;} 
} 

我的輸入是

Class A 
--------------------- 
RecordID name 

1  Sathish 

2  Sathish 

3  Kumar 

4  Kumar 

5  Ajay 

Class B 
-------------------------------------- 
Name DataToPick 

Sathish 1 

kumar  2 

現在我想加入兩個表，並從A類獲得值，即3個記錄，基於B類變量（Datatopick）

請幫忙寫下如下的LINQ

var qry= (from c in classA 
      join d in ClassB on c.name equals d.name 
     select c).take(d.datatopick) 

Answer 1

您可以將ClassA組合起來，然後從另一個列表中選擇DataToPick。

var result = 
    classA.GroupBy(a => a.Name) 
      .SelectMany(g => g.Take(classB.Where(b => b.Name == g.Key) 
             .Select(b => b.DataToPick) 
             .DefaultIfEmpty(0) 
             .Single())); 

更妙的是加入第一和看法：

var result = classA.Join(classB, a => a.Name, b => b.Name, (a, b) => new {a, b.DataToPick}) 
        .GroupBy(arg => new {arg.a.Name, arg.DataToPick}) 
        .SelectMany(g => g.Select(arg => arg.a).Take(g.Key.DataToPick)); 

Answer 2

你可以join ClassA和ClassB的，由Name, DataToPick組，並使用Take像

(from a in listA 
join b in listB on a.Name equals b.Name 
group new { a, b } by new { a.Name, b.DataToPick } into gr 
select new 
{ 
    Name = gr.Key.Name, 
    ListA = gr.Select(x=>x.a).Take(gr.Key.DataToPick) 
} 
).SelectMany(x => x.ListA).ToList();