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();

但我需要这样的事情：

        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

如何像这样使用Enumerable.Cast<T>()？

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的类型为Comment

Answer 2

尝试：

var queryResult = (from post in context.Posts
                select new
                           {
                               post,
                               post.Author,
                               post.Tags,
                               post.Categories,
                               Count = context.Comments.Where(c => c.Post == post).Where(c => IsPublic == 1).Count()
                           }).ToList();

Answer 3

这有效：

        var queryResult = (from post in posts
                           join comment in comments.Where(x=> x.IsPublic) on post.Id equals comment.Post.Id into g
                    select new
                               {
                                   post,
                                   post.Author,
                                   post.Tags,
                                   post.Categories,
                                   Count = g.Count()
                               })

但是在所有解决方案中我们都遇到了这个问题How to use Include and Anonymous Type in same query in Entity Framework?

Answer 4

我是按照LukLed的说法写的，但为了使它能够工作，我将使用Post实体的PK：

var queryResult = (from post in context.Posts
                select new
                           {
                               post,
                               post.Author,
                               post.Tags,
                               post.Categories,
                               Count = context.Comments.Where(c => c.Post.Id == post.Id && c.IsPublic == 1).Count()
                           }).ToList();

或Post.Id可以写为PostId，如果通过关联公开forign键，我相信它会更有效率。

如何使用实体框架中的位置计算关联实体

4 个答案: