c# - 如何使用 Entity Framework 中的 Where 计算关联实体

Question

我有这个:

        var queryResult = (from post in posts
                    select new
                               {
                                   post,
                                   post.Author,
                                   post.Tags,
                                   post.Categories,
                                   Count = post.Comments.Count()
                               }).ToList();

但是我需要这样的东西:

        var queryResult = (from post in posts
                    select new
                               {
                                   post,
                                   post.Author,
                                   post.Tags,
                                   post.Categories,
                                   Count = post.Comments.Where(x=>x.IsPublic).Count()
                               }).ToList();

但是 post.Comments 是一个 ICollection

Answer 1

如何使用 Enumerable.Cast<T>() 像这样？

var queryResult = (from post in posts
                    select new
                               {
                                   post,
                                   post.Author,
                                   post.Tags,
                                   post.Categories,
                                   Count = post.Comments.Cast<Comment>()
                                                        .Where(x=>x.IsPublic).Count()
                               }).ToList();

假设post.Comments类型为 Comment