如何通過在這種情況下使用lambda或linq來避免使用嵌套的foreach語句？

Question

如何通過在這種情況下使用lambda或linq來避免使用嵌套的foreach語句？現在已經很晚了，我似乎無法弄清楚如何訪問ErrorMessage屬性而不必恢復到嵌套的foreach語句。如果完全使用Lambda或Linq重寫代碼，那麼等效方法是什麼？

public static List<String> ExtractErrors(this ModelStateDictionary modelStateDictionary) 
     { 
      List<String> errors = new List<String>(); 

      var modelErrorCollection = (from modelState in modelStateDictionary.Values 
             where modelState.Errors != null && modelState.Errors.Count > 0 
             select modelState.Errors).ToList(); 

      foreach (var item in modelErrorCollection) 
      { 
       foreach (ModelError modelError in item) 
       { 
        errors.Add(modelError.ErrorMessage); 
       } 
      } 

      return errors; 
     } 

Answer 1

你要使用SelectMany這個

public static List<String> ExtractErrors(this ModelStateDictionary modelStateDictionary) 
    { 
     var modelErrorCollection = (from modelState in modelStateDictionary.Values 
            where modelState.Errors != null && modelState.Errors.Count > 0 
            select modelState.Errors) 
            .SelectMany(item=>item) 
            .Select(modelError=>modelError.ErrorMessage) 
            .ToList(); 
     return modelErrorCollection; 
    } 

Answer 2

是不是errors.Add(modelErrorCollection.SelectMany(x => x))？