asp.net mvc中的分页

Question

I have categories and subcategories. Each subcategory has some products. eg programming category has | C# , java , basic subcategories | where c# has c# 3 , c# 3.5 products | java has java ee , java me and so on

I want to select 10 products from categories using linq to EF.

The problem is that I don't want to load all products from the database and then sort them and then select 10 of them.

I want a solution which i can just take 10 products from database without transferring all products from the database back to web server.

I know that EF is greedy and would take only 10 products and skip some. but in my case which i have categories and subcategories so I think I should first select all products from different subcategories belonging to a category and append them to a list which cause bringing all products to server and then select 10 of them.

What is the best practice so that i don't have to transfer all products to server?

Answer 1

You can do this in one query:

var pagedProducts = _db.Categories.Join( 
    _db.Products,
    c => c.CategoryId,
    p => p.CategoryId,
    (Category, Products) =>
       new
       {
           CategoryType = Category,
           ItsProducts  = Products
       })
        .OrderBy(g => g.Category.Name)
        .Skip((CurrentPage - 1) * pageSize)
        .Take(pageSize);