LINQ -如何获得单一()审查

Question

这是我获取第一篇书评的重复器:

<asp:Repeater ID="Repeater2" runat="server">
    <ItemTemplate>
        <asp:Repeater ID="Repeater1" runat="server" DataSource='<%# Eval("Reviews") %>' ItemType="ELibraryModel.Review">
        <ItemTemplate>
        <div class="new_prod_box">
           <div class="new_prod_bg">
               <asp:HyperLink ID="HyperLink1" CssClass="thumb" runat="server" ImageUrl='<%# String.Format("../Images/books/{0}.jpg", Item.Id.ToString()) %>' Text='<%# Item.Title %>' NavigateUrl='<%# "../books/bookdetails.aspx?reviewId=" + Item.Id.ToString() %>'></asp:HyperLink>
               <a><asp:Label ID="DescriptionLabel" runat="server" Text='<%# Item.Title %>' /></a>
           </div>
        </div>
    </ItemTemplate>
</asp:Repeater>

在代码后面，我使用这样的东西来获得第一次审查，它工作:

using (ELibraryEntities entities = new ELibraryEntities())
{
    var firstBook = (from books in entities.Books.Include("Reviews")
                     orderby books.Category
                     select new { books.Reviews }).Take(1);
    Repeater2.DataSource = firstBook;
    Repeater2.DataBind();
}

如何根据评论Id获得我想要的评论。

我正在尝试这样做:

using (ELibraryEntities entities = new ELibraryEntities())
{
    var review = (from books in entities.Books.Include("Reviews")
                  where books.Id == 13
                  orderby books.Category
                  select new { books.Reviews }).Single();
    Repeater2.DataSource = review;
    Repeater2.DataBind();
}

但它不起作用。问题是我无法访问Reviews表的Id。books.Id == 13属于Books表

我需要改变后面和中继器的代码吗?

谢谢。

Answer 1

试试这个:

using (ELibraryEntities entities = new ELibraryEntities())
{
    var review = (from review in entities.Reviews
                  where review.BookId == BookId
                  select review).FirstOrDefault();
    Repeater2.DataSource = review;
    Repeater2.DataBind();
}

使用上面的代码片段，您可以从评论中获得第一篇评论，该评论是为Id等于给定的书BookId编写的。

注释:如果本书至少有一个评论，您将获得第一个评论。否则，查询结果将为空。

有关FirstOrDefault方法如何工作的更多说明，请查看此处