I have a database that unfortunately have no real foreign keys (I plan
to add this later, but prefer not
to do it right now
to make migration easier). I have manually written domain
objects that map
to the database
to set up relationships (following this tutorial http://www.codeproject.com/Articles/43025/A-LINQ-Tutorial-Mapping-Tables-to-Objects), and I've finally gotten the code
to run properly. However, I've noticed I now have the SELECT N + 1 problem. Instead of selecting all Product's they're selected one by one with this SQL:
SELECT [t0].[id] AS [ProductID], [t0].[Name], [t0].[info] AS [Description]
FROM [products] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [65]
Controller:
public ViewResult List(string category, int page = 1)
{
var cat = categoriesRepository.Categories.SelectMany(c => c.LocalizedCategories).Where(lc => lc.CountryID == 1).First(lc => lc.Name == category).Category;
var productsToShow = cat.Products;
var viewModel = new ProductsListViewModel
{
Products = productsToShow.Skip((page - 1) * PageSize).Take(PageSize).ToList(),
PagingInfo = new PagingInfo
{
CurrentPage = page,
ItemsPerPage = PageSize,
TotalItems = productsToShow.Count()
},
CurrentCategory = cat
};
return View("List", viewModel);
}
Since I wasn't sure if my
LINQ expression was correct I tried
to just use this but I still got N+1:
var cat = categoriesRepository.Categories.First();
Domain objects:
[Table(Name = "products")]
public class Product
{
[Column(Name = "id", IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert)]
public int ProductID { get; set; }
[Column]
public string Name { get; set; }
[Column(Name = "info")]
public string Description { get; set; }
private EntitySet<ProductCategory> _productCategories = new EntitySet<ProductCategory>();
[System.Data.
Linq.Mapping.Association(Storage = "_productCategories", OtherKey = "productId", ThisKey = "ProductID")]
private ICollection<ProductCategory> ProductCategories
{
get { return _productCategories; }
set { _productCategories.Assign(value); }
}
public ICollection<Category> Categories
{
get { return (from pc in ProductCategories select pc.Category).ToList(); }
}
}
[Table(Name = "products_menu")]
class ProductCategory
{
[Column(IsPrimaryKey = true, Name = "products_id")]
private int productId;
private EntityRef<Product> _product = new EntityRef<Product>();
[System.Data.
Linq.Mapping.Association(Storage = "_product", ThisKey = "productId")]
public Product Product
{
get { return _product.Entity; }
set { _product.Entity = value; }
}
[Column(IsPrimaryKey = true, Name = "products_types_id")]
private int categoryId;
private EntityRef<Category> _category = new EntityRef<Category>();
[System.Data.
Linq.Mapping.Association(Storage = "_category", ThisKey = "categoryId")]
public Category Category
{
get { return _category.Entity; }
set { _category.Entity = value; }
}
}
[Table(Name = "products_types")]
public class Category
{
[Column(Name = "id", IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert)]
public int CategoryID { get; set; }
private EntitySet<ProductCategory> _productCategories = new EntitySet<ProductCategory>();
[System.Data.
Linq.Mapping.Association(Storage = "_productCategories", OtherKey = "categoryId", ThisKey = "CategoryID")]
private ICollection<ProductCategory> ProductCategories
{
get { return _productCategories; }
set { _productCategories.Assign(value); }
}
public ICollection<Product> Products
{
get { return (from pc in ProductCategories select pc.Product).ToList(); }
}
private EntitySet<LocalizedCategory> _LocalizedCategories = new EntitySet<LocalizedCategory>();
[System.Data.
Linq.Mapping.Association(Storage = "_LocalizedCategories", OtherKey = "CategoryID")]
public ICollection<LocalizedCategory> LocalizedCategories
{
get { return _LocalizedCategories; }
set { _LocalizedCategories.Assign(value); }
}
}
[Table(Name = "products_types_localized")]
public class LocalizedCategory
{
[Column(Name = "id", IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert)]
public int LocalizedCategoryID { get; set; }
[Column(Name = "products_types_id")]
private int CategoryID;
private EntityRef<Category> _Category = new EntityRef<Category>();
[System.Data.
Linq.Mapping.Association(Storage = "_Category", ThisKey = "CategoryID")]
public Category Category
{
get { return _Category.Entity; }
set { _Category.Entity = value; }
}
[Column(Name = "country_id")]
public int CountryID { get; set; }
[Column]
public string Name { get; set; }
}
I've tried
to comment out everything from my View, so nothing there seems
to influence this. The ViewModel is as simple as it looks, so shouldn't be anything there.
When reading this ( http://www.hookedonlinq.com/LinqToSQL5MinuteOVerview.ashx) I started suspecting it might be because I have no real foreign keys in the database and that I might need
to use manual joins in my code. Is that correct? How would I go about it? Should I remove my mapping code from my domain model or is it something that I need
to add/change
to it?
Note: I've stripped parts of the code out that I don't think is relevant
to make it cleaner for this question. Please let me know if something is missing.
