Relationships between tables mvc3 - asp.net-mvc-3

Question

I'm building website in MVC 3.
i am using EF code first in existing database.
my ET inside the model look like that:
public class Pages
{
[Required]
public int ID { get; set; }
public int ParentID { get; set; }
[Required]
public int PageType { get; set; }
[Required]
[DataType(DataType.Text)]
[DisplayName("כותרת")]
public string Title { get; set; }
public string SearchWords { get; set; }
public string Leng { get; set; }
public int? Sort { get; set; }
public string Modules { get; set; }
[ForeignKey("PageType")]
public virtual PagesType Type { get; set; }
public virtual IEnumerable<PagesType> Types { get; set; }
[ForeignKey("PageID")]
public ICollection<PageContent> PageContent { get; set; }
[ForeignKey("PageID")]
public virtual ICollection<ImagesTable> Images { get; set; }
}
public class PageContent
{
public int ID { get; set; }
public int PageID { get; set; }
public string Header { get; set; }
public string Text { get; set; }
[ForeignKey("ID")]
public virtual ICollection<Pages> Pages { get; set; }
}
as you see in my fist table that cold Pages i have a relationship to another table that named PageContent.
in my Pages class i had this code
[ForeignKey("PageID")]
public ICollection<PageContent> PageContent { get; set; }
now, when i trying to add new pageContent into new page i get an error.
see this code
public ActionResult AddPage(PageModel page)
{
SystemLogic cmd = new SystemLogic();
page.Leng = "he";
Models.Pages p = new Pages();
p.ParentID = page.ParentID;
PageContent pageContent = new PageContent();
pageContent.Text = page.Content;
p.PageContent.Add(pageContent);
The error is
Object reference not set to an instance of an object.
What i did wrong?

Answer 1

You will get the NRE at p.PageContent.Add(pageContent); because the collection is not initialized. Initialize the collections inside the constructor of Pages class.
public class Pages
{
public Pages()
{
PageContent = List<PageContent>();
Images = List<ImagesTable>();
}
[Required]
public int ID { get; set; }
public int ParentID { get; set; }
[Required]
public int PageType { get; set; }
[Required]
[DataType(DataType.Text)]
[DisplayName("כותרת")]
public string Title { get; set; }
public string SearchWords { get; set; }
public string Leng { get; set; }
public int? Sort { get; set; }
public string Modules { get; set; }
[ForeignKey("PageType")]
public virtual PagesType Type { get; set; }
public virtual IEnumerable<PagesType> Types { get; set; }
[ForeignKey("PageID")]
public ICollection<PageContent> PageContent { get; set; }
[ForeignKey("PageID")]
public virtual ICollection<ImagesTable> Images { get; set; }
}
Or before you add objects to the collection
if (p.PageContent == null) p.PageContent = new List<PageContent>();
p.PageContent.Add(pageContent);
You should consider using proper naming conventions(eg Page instead of Pages).