Question

我有一个名为Tag的班级。每个标记都有一些News，Article和“轮询”。我想要Get All Related Post哪个有Tag。为此，我使用此查询：

 public Tag Get(string tagName, int page, int recordsPerPage = 10)
    {
        int skip = page * recordsPerPage;
        return 
            _tags.Where(tag => tag.Title.ToLower() == tagName.ToLower()).Include(row => row.Articles
            .OrderByDescending(n => n.Code).Skip(skip).Take(recordsPerPage).ToList())
            .Include(row => row.News.AsQueryable()).OrderBy(news => news.Code).Skip(skip).Take(recordsPerPage)
            .Include(row => row.Polls).OrderByDescending(poll => poll.Code).Skip(skip).Take(recordsPerPage).FirstOrDefault();
}

但是当我运行Project I时出现此错误：

Include路径表达式必须引用在类型上定义的导航属性。使用虚线路径作为参考导航属性，使用Select运算符作为集合导航属性。

Answer 1

您不能将表达式传递给Include方法，该方法不是属性表达式，请查看代码

.Include(row => row.Articles.OrderByDescending(n => n.Code).Skip(skip).Take(recordsPerPage).ToList())


.Include(row => row.News.AsQueryable())

正如你所看到的，在include中，你正在调用许多方法，而且不允许这样做。

您必须为此更改：

.Include(row => row.Articles)
.Include(row => row.News)

让我尝试改进您的代码，您当前的代码是这样的：

_tags.Where(tag => tag.Title.ToLower() == tagName.ToLower()).Include(row => row.Articles
            .OrderByDescending(n => n.Code).Skip(skip).Take(recordsPerPage).ToList())
            .Include(row => row.News.AsQueryable()).OrderBy(news => news.Code).Skip(skip).Take(recordsPerPage)
            .Include(row => row.Polls).OrderByDescending(poll => poll.Code).Skip(skip).Take(recordsPerPage).FirstOrDefault();

让我们在换行符中打破它

_tags.Where(tag => tag.Title.ToLower() == tagName.ToLower())
     .Include(row => row.Articles.OrderByDescending(n => n.Code).Skip(skip).Take(recordsPerPage).ToList())
     .Include(row => row.News.AsQueryable())
     .OrderBy(news => news.Code)
     .Skip(skip)
     .Take(recordsPerPage)
     .Include(row => row.Polls)
     .OrderByDescending(poll => poll.Code)
     .Skip(skip)
     .Take(recordsPerPage)
     .FirstOrDefault();

如果您只需要一个标记，则无需将此大方法链接起来，您可以使用此方法简化：

public Tag Get(string tagName, int page, int recordsPerPage = 10)
{
    return _tags.Include(tag => row.Articles).Include(tag => row.News).Include(tag => row.Polls)
         .OrderBy(tag => news.Code)
         .FirstOrDefault(tag => tag.Title.ToLower() == tagName.ToLower());
}

如何申请Skip and Take on Include

1 个答案: