linq - EF - 无法从 System.Linq.IQueryable 转换为 System.Data.Objects.ObjectQuery

Question

在我使用 .Except 方法时，我需要从 allCategories 中减去 contentCategories 的结果，但我收到一个错误。

知道我做错了什么......非常感谢

Error   2   Argument 1: cannot convert from 'System.Linq.IQueryable<System.Data.Objects.DataClasses.EntityCollection<WebProject.DataAccess.DatabaseModels.CmsCategory>>' to 'System.Data.Objects.ObjectQuery<WebProject.DataAccess.DatabaseModels.CmsCategory>'

---

            int contentId = Int32.Parse(uxContentsListSelector.SelectedValue);
            var allCategories = from category in context.CmsCategories select category;
            var contentCategories = from content in context.CmsContents
                                          where content.ContentId == contentId
                                          select content.CmsCategories;
            var result = context.CmsCategories.Except(contentCategories);

Answer 1

您需要添加一个额外的 from in 子句以获得扁平化列表。

var contentCategories = from content in context.CmsContents
                        from cat in content.CmsCategories
                        where content.ContentId == contentId
                        select cat;

然后我会将您的Except 方法更改为Any 方法

var result = context.CmsCategories.Where(cat => !contentCategories.Any(c => c.CategoryId == cat.CategoryId));