我如何使用Linq和ASP.Net Forms编写多个表之间的连接

Question

我已经实现了一个可以工作的解决方案，但是LINQ对我来说是一件小事，我正在努力寻找所需的信息。

以下是我有：

var prodCat = from pc in db.ProductCategories 
       where pc.Category == Int32.Parse(CategoriesDropper.SelectedValue) 
       select pc; 

List<int> productIds = new List<int>(); 
foreach (var pc in prodCat) 
{ 
    productIds.Add(pc.Product); 
} 

var products = from p in db.Products 
       where productIds.Contains(p.Id) 
       select p; 

ProductsGridView.DataSource = products; 
ProductsGridView.DataBind(); 

我非常希望有一个单一的选择，而不是两个，以达到同样的效果。

Answer 1

var products = from pc in db.ProductCategories 
       join p in db.Products on pc.Product equals p.Id 
       where pc.Category == Int32.Parse(CategoriesDropper.SelectedValue) 
       select p; 

ProductsGridView.DataSource = products; 
ProductsGridView.DataBind(); 

查看LINQ - Join Operators in C# for Visual Studio 2010仅供参考。

希望这会有所帮助！

Answer 2

你没有提到你正在使用的LINQ的味道，但假设你有ProductCategories与产品之间设置的关联，你应该能够做这样的事情：

int Cat = Int32.Parse(CategoriesDropper.SelectedValue); 
var products = from pc in db.ProductCategories 
       where pc.Category == cat 
       from p in pc.Products 
       select p; 

Answer 3

var selectedCategory = Int32.Parse(CategoriesDropper.SelectedValue); //Parse the value once 
var products = 
    from p in db.Products //foreach product in the database 
    join pc in db.ProductCategories 
    on pc.Product equals p.Id //where the Ids match 
    where pc.Category == selectedCategory //and with the same category 
    select p; //select the product 
ProductsGridView.DataSource = products; 
ProductsGridView.DataBind();