我有这个 LINQ
var questions = _context.Questions
.Where(q => q.Level.Level == level)
.Select(q => new QuestionViewModel
{
Text = q.Text,
Id = q.Id,
IsMultiSelected = q.IsMultiSelected,
AnswerViewModels = q.Answers
.Select(
a => new AnswerViewModel
{
Checked = false,
Text = a.Text,
Id = a.Id
}) as List<AnswerViewModel>
});
return questions.ToList();
我明白了
Exception Details: System.NotSupportedException: The 'TypeAs' expression with an input of type 'System.Collections.Generic.IEnumerable`1' and a check of type 'System.Collections.Generic.List`1' is not supported. Only entity types and complex types are supported in LINQ to Entities queries.
在
return questions.ToList();
我不在选择中使用匿名类型。如何解决此错误?
更新
我编写了一些解决方案
List<QuestionViewModel> result = new List<QuestionViewModel>();
var questions = from q in _context.Questions
where q.Level.Level == level
select new QuestionViewModel()
{
Text = q.Text,
Id = q.Id,
IsMultiSelected = q.IsMultiSelected,
AnswerViewModels = from a in q.Answers
select new AnswerViewModel
{
Text = a.Text,
Id = a.Id,
Checked = false
}
};
var qList = questions.ToList();
for(int i = 0; i < questions.Count(); i++)
{
var q = qList[i]; //question
var a = q.AnswerViewModels.ToList(); //answers for question
var answers = new List<AnswerViewModel>(); //List answers
for(int j = 0; j < a.Count(); j++)
{
//add new Answer from IEnumerable<AnswerViewQuestion> to List<...>
answers.Add(new AnswerViewModel
{
Checked = false,
Id = a[j].Id,
Text = a[j].Text
});
}
result.Add(q);
}
如何优化?
最佳答案
问题在于
.Select(a => new AnswerViewModel { ... }) as List<AnswerViewModel>
应该是
.Select(a => new AnswerViewModel { ... }).ToList()
原因是将 LINQ 生成的 IEnumerable
转换为 List
的正确方法当然是调用 ToList
扩展方法,你已经在最后一行中做了。
关于c# - 如何正确地将 IEnumerable<T> 转换为 List<T>?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/10381382/