c# - LINQ to Entities 无法识别方法 'System.Threading.Tasks.Task`

Question

我该如何解决这个问题？

An exception of type 'System.NotSupportedException' occurred in EntityFramework.SqlServer.dll but was not handled in user code

Additional information: LINQ to Entities does not recognize the method 'System.Threading.Tasks.Task`1[Jahan.Blog.Model.Identity.User] FindByIdAsync(Int32)' method, and this method cannot be translated into a store expression.

 public virtual User User { get; set; }
 private IQueryable<ArticleGridViewModel> Query()
 {
    ArticleRepository repository = new ArticleRepository();
    IQueryable<ArticleGridViewModel> query = repository.FindAll().Select(article => new     ArticleGridViewModel
    {
       Tags = article.ArticleTags.Where(c => c.ArticleId == article.Id).Select(b => b.Tag).Distinct().ToList(),
       NumberOfComments = article.Comments.Count(c => c.ArticleId == article.Id),
       AttachmentFiles =article.AttachmentFiles.Where(a => a.ArticleId == article.Id).Distinct().ToList(),
       CreatedDate = article.CreatedDate,
       IsActive = article.IsActive,
       IsActiveNewComment = article.IsActiveNewComment,
       LikeCounter = article.LikeCounter,
       ModifiedDate = article.ModifiedDate,
       RateCounter = article.RateCounter,
       Title = article.Title,
       UserId = article.UserId,
       Comments = Comments.Where(c => c.ArticleId == article.Id).ToList(),



       User = AppUserStore.Instance.FindByIdAsync(article.Id).Result, // The error happened because of this line of code.

   });
   return query;
 }

 public virtual IQueryable<ArticleGridViewModel> QueryByCriteria(Expression<Func<ArticleGridViewModel, bool>> predicate = null, params Expression<Func<ArticleGridViewModel, object>>[] includeProperties)
    {
        IQueryable<ArticleGridViewModel> items = Query();
        if (includeProperties != null)
        {
            foreach (var includeProperty in includeProperties)
            {
                items = items.Include(includeProperty);
            }
        }
        if (predicate != null)
            return items.Where(predicate);
        return items;
    }
    public virtual IEnumerable<ArticleGridViewModel> FindAll(Expression<Func<ArticleGridViewModel, bool>> predicate = null, params Expression<Func<ArticleGridViewModel, object>>[] includeProperties)
    {
        List<ArticleGridViewModel> result = QueryByCriteria(predicate, includeProperties).ToList();
        return result;
    }

Answer 1

.Select(x=>) 语句中的所有内容都必须能够转换为 SQL 表达式。这就是为什么尝试使用 .ToString()(示例)在某些情况下可能会失败并出现相同的错误。

基本上，EF 不知道如何将 System.Threading.Tasks.Task 的对象转换为 SQL 语句。

鉴于您正在尝试使用从查询中检索到的值来调用它，您很可能需要要么

1. 循环 .Select() 方法的结果并为每个结果运行此函数以设置用户属性，或者，
2. 自己在该行中实现逻辑，而不是调用函数，就像您在其他地方使用 where 子句那样。