Can't form some simple POCO's to use with "Code First" Entity Framework, please check for mistake - asp.net-mvc-3

Question

So I decided to go with the code first/DbContext approach, but already have an existing database file. Nothing complex, so I am thinking I can just create the DbContext derived container class with DbSets for the respective POCO's, create the connection string to my database and I should be set. However I believe I am having difficulties properly declaring the properties in my entity classes since I am getting errors when trying access an object through the navigational properties. Usually telling me Object reference not set to an instance of an object when I try context.Products.Find(1).Category.CATNAME; etc. Also tried declaring the collection properties with virtual keyword to no avail.
Some specifics of the database schema are:
In Categories table the PCATID is a foreign key to the CategoryID in
the same Categories table and can be null.
Both CategoryID and RootCategoryID in Products table can be null and
are both foreign keys to CategoryID in the Categories table.
I am testing things at the moment but will be setting a lot of the fields to non null types eventually.
Here are my entity POCO's and the entity Dbset container class:
public class Category
{
[Key]
public int CategoryID { get; set; }
public string CATNAME { get; set; }
public int PCATID { get; set; }
public ICollection<Category> Categories { get; set; }
public ICollection<Product> Products { get; set; }
}
public class Product
{
[Key]
public int ProductID { get; set; }
public int CategoryID { get; set; }
public int RootCategoryID { get; set; }
public string Name { get; set; }
public string ShortDescription { get; set; }
public string LongDescription { get; set; }
public string Keywords { get; set; }
public decimal ListPrice { get; set; }
public Category Category { get; set; }
}
public class EFDbContext: DbContext
{
public DbSet<Product> Products { get; set; }
public DbSet<Category> Categories { get; set; }
}

Answer 1

You need to make PCATID a nullable property as you have said it can be null. Make all those navigation properties and collection properties virtual. EF will not be able to detect the category hierarchy so you have use either attributes or fluent API to configure that.
public class Category
{
[Key]
public int CategoryID { get; set; }
public string CATNAME { get; set; }
[ForeignKey("ParentCategory")]
public int? PCATID { get; set; }
[InverseProperty("Categories")]
public virtual Category ParentCategory { get; set; }
[InverseProperty("ParentCategory")]
public virtual ICollection<Category> Categories { get; set; }
public virtual ICollection<Product> Products { get; set; }
}

Answer 2

Requirements for Creating POCO Proxies
Everything looks ready for POCO but Lazy Loading isn't sorted out at this point. By default LL is on, but in order to enable lazy loading, the Category property must be Virtual (a proxy is created that catches the reference and loads the data). If you don't want lazy loading then disable it in your EFDbContext constructor.
So your options are:
public virtual Category Category { get; set; }
or
public class EFDbContext: DbContext
{
public static EFDbContext()
{
LazyLoadingEnabled = false
}
...
}
You'd probably want to do the first one...

Answer 3

Are you certain you really want to use Code First? Or do you just want to use DbContext and DbSet? You can get the same benefits with Database First, using DbContext and DbSet. Since you already have a database, it's generally a lot simpler.
See: http://blogs.msdn.com/b/adonet/archive/2011/03/15/ef-4-1-model-amp-database-first-walkthrough.aspx
The only difference between Code First and Database First with DbContext is that Code first uses the fluent mapping model, while Database First uses an .edmx file. Maintaining the .edmx is much easier with an existing database.
If you're bound and determined to use Code First, then I suggest getting the Entity Framework Power Tools CTP1 and reverse engineering your database to Code First.

Answer 4

I agree with #Eranga about class Category (+1 to #Eranga).
public class Category {
[Key]
public int CategoryID { get; set; }
public string CATNAME { get; set; }
[ForeignKey("ParentCategory")]
public int? PCATID { get; set; }
[InverseProperty("Categories")]
public virtual Category ParentCategory { get; set; }
[InverseProperty("ParentCategory")]
public virtual ICollection<Category> Categories { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
And you also have problem with your Linq query:
context.Products.Find(1).Category.CATNAME;
EF return data only from tables that you request with Include or you use this tables in functions.
With this code all work:
db.Products
.Include(p => p.Category) // here I demand to load data from Category table
.First(p => p.ProductID == 3)
.Category
.CATNAME;