LINQ - 類型參數不能在選擇

Question

從使用推斷出我有以下其中objectiveData是：IEnumerable<Objective>

public IList<Objective> createObjectives() 
    { 
     var objectiveData = GetContent.GetType5(); 
     var objectives = objectiveData.Select(o => { 
      var result = new Objective { 
          Name = o.Name, 
          Text = o.Text 
      }; 
      if (o.Name != null && o.Name.EndsWith("01")) 
      { 
       result.ObjectiveDetails.Add 
       (
        new ObjectiveDetail 
        { 
         Text = o.Text 
        } 
       ); 
      } 
     }); 
     return objectives.ToList(); 
    } 

我正在上線的誤差與「選擇」的說法：

The type arguments for method 'System.Linq.Enumerable.Select<TSource,TResult> 
(System.Collections.Generic.IEnumerable<TSource>, System.Func<TSource,int,TResult>)' 
cannot be inferred from the usage. Try specifying the type arguments explicitly. 

這裏是我的對象類別：

public partial class Objective : AuditableTable 
{ 
    public Objective() 
    { 
     this.ObjectiveDetails = new List<ObjectiveDetail>(); 
    } 
    public int ObjectiveId { get; set; } 
    public string Name { get; set; } 
    public string Text { get; set; } 
    public virtual ICollection<ObjectiveDetail> ObjectiveDetails { get; set; } 
} 

Answer 1

var objectives = objectiveData.Select(o => { 
     var result = new Objective { 
         Name = o.Name, 
         Text = o.Text 
     }; 
     if (o.Name != null && o.Name.EndsWith("01")) 
     { 
      result.ObjectiveDetails.Add 
      (
       new ObjectiveDetail 
       { 
        Text = o.Text 
       } 
      ); 
     } 
     //you miss this 
     return result; 
    }); 

Answer 2

你需要

return result; 

在你表達的結尾。

Answer 3

首先，LINQ和副作用......好，壞。由於延遲加載和其他許多問題。但是，你需要的是增加一個return result;線在隨後結束您的代碼如下所示：

var objectives = objectiveData.Select(o => { 
     var result = new Objective { 
         Name = o.Name, 
         Text = o.Text 
     }; 
     if (o.Name != null && o.Name.EndsWith("01")) 
     { 
      result.ObjectiveDetails.Add 
      (
       new ObjectiveDetail 
       { 
        Text = o.Text 
       } 
      ); 
     } 
     return result; 
    }); 

然而，對於這個以更正規的方式表現，我會做這樣的：

var objectives = 
    objectiveData.Select(o => new Objective { Name = o.Name, Text = o.Text}) 
result.ObjectiveDetails.AddRange(
    objectiveData.Where(o => (o.Name ?? "").EndsWith("01")) 
       .Select(o => new ObjectiveDetail { Text = o.Text }));