Model count = null - asp.net-mvc

Question

I'm rewriting this question:
I have 2 models. Entry and Topic.
public class Entry
{
public int EntryId { get; set; }
public int UserId { get; set; }
public int TopicId { get; set; }
public String EntryQuestion { get; set; }
public String EntryAnswer { get; set; }
public int EntryReview { get; set; }
public String QuestionValidationURL { get; set; }
public virtual ICollection<Topic> TopicList { get; set; }
}
public class Topic
{
public int TopicId { get; set; }
public String TopicName { get; set; }
}
I followed an example on ASP.Net/MVC to set up my models this way.
What I would like to do is for every entry item I have a TopicId, but then I'd like to convert that to a TopicName by accessing my TopicList.
My question is, how do I load TopicList?
In the examples I'm following I'm seeing something about LazyLoading and EagerLoading, but it doesn't seem to be working.
I tried doing the following from my Entry controller:
db.Entries.Include(x => x.TopicList).Load();
But that still gives me a TopicList of 0 (which is better than null)
How can I do this?
In my view I'm binding to the Entries like this:
#model IEnumerable<projectInterview.Models.Entry>
I would like to access the TopicList here:
#foreach (var item in Model) {
<tr>
<td>
#Html.DisplayFor(modelItem => item.TopicId)
</td>
...
</tr>
I'd like to use the TopicId in this loop and display the TopicName that is part of the object in the collection.

Answer 1

I'm assuming you're following an Entity Framework example. You're trying to create a one-to-many relationship, as far as I can tell, although I'm unsure about which end is which.
In the general case, to establish a one-to-many relationship, you have to do something like this:
public class One
{
[Key]
public int Id { get; set; }
public virtual ICollection<Many> Many { get; set; }
}
public class Many
{
[Key]
public int Id { get; set; }
[ForeignKey("One")]
public int OneId { get; set; }
public virtual One One { get; set; }
}
If what you're trying to do is have one Entry relating to many Topic objects, then you're almost there but you're lacking something.
For the ICollection<Topic> to actually contain anything, the (many) Topic objects need to have a foreign key to the (one) Entry. (It also doesn't hurt to explicitly mark the primary key on both sides, rather than relying on the EF conventions.)
public class Topic
{
[Key]
public int TopicId { get; set; }
public String TopicName { get; set; }
[ForeignKey("Entry")]
public int EntryId { get; set; }
public virtual Entry Entry { get; set; }
}
public class Entry
{
[Key]
public int EntryId { get; set; }
public int UserId { get; set; }
public int TopicId { get; set; }
public String EntryQuestion { get; set; }
public String EntryAnswer { get; set; }
public int EntryReview { get; set; }
public String QuestionValidationURL { get; set; }
public virtual ICollection<Topic> TopicList { get; set; }
}
Now TopicList should be an actual and populated collection, without the need to do an Include.
If, on the other hand, you want one Topic relating to many Entry objects, then you have it a little backwards. The correct way would be:
public class Topic
{
[Key]
public int TopicId { get; set; }
public String TopicName { get; set; }
public virtual ICollection <Entry> Entries { get; set; }
}
public class Entry
{
[Key]
public int EntryId { get; set; }
public int UserId { get; set; }
public String EntryQuestion { get; set; }
public String EntryAnswer { get; set; }
public int EntryReview { get; set; }
public String QuestionValidationURL { get; set; }
[ForeignKey("Topic")]
public int TopicId { get; set; }
public virtual Topic Topic { get; set; }
}
In this case, you may or may not use db.Entries.Include(x => x.Topic) depending on whether you want them loaded all at once or one-by-one on demand. Regardless of what you choose, the following expression should return the proper value:
myEntry.Topic.TopicName

Answer 2

If I understand you correctly you have added the list of Topics to the Entry just to get the name of the topic when displaying the entry. The best way to do this is to actually have a Topic property in your entry model. So your model would look like this:
public class Entry
{
public int EntryId { get; set; }
public int UserId { get; set; }
public int TopicId { get; set; }
public String EntryQuestion { get; set; }
public String EntryAnswer { get; set; }
public int EntryReview { get; set; }
public String QuestionValidationURL { get; set; }
//Change this.....
public virtual Topic Topic { get; set; }
}
Then in your view you would use (assuming the Model is an IEnumerable):
#foreach (var item in Model) {
<tr>
<td>
#Html.DisplayFor(modelItem => modelItem.Topic.TopicName )
</td>
...
</tr>
This link has a great example of how to do this:
http://weblogs.asp.net/manavi/archive/2011/03/28/associations-in-ef-4-1-code-first-part-2-complex-types.aspx

Answer 3

In my opinion problem is with casting. In view you have IEnumerable<projectInterview.Models.Entry> while Topics is ICollection<Topic>, which is a collection of different type

Answer 4

Topics = null means there are no Topics in the list to iterate over. How do you fill them? Your view expects IEnumerable how do you cast your topics to the entries?
Based on the original question I've added a small working example, maybe it helps you to find your bug.
Controller:
public class TestController : Controller
{
public ActionResult Index()
{
var viewModel = new ViewModel()
{
Topics = new List<Topic>()
};
viewModel.Topics.Add(new Topic() { header = "test" });
viewModel.Topics.Add(new Topic() { header = "test2" });
return View(viewModel);
}
}
Model:
public class ViewModel
{
public virtual ICollection<Topic> Topics { get; set; }
public int getCount()
{
return Topics.Count;
}
}
public class Topic
{
public string header { get; set; }
}
View:
#model testProject.Models.ViewModel
#{
ViewBag.Title = "Index";
}
<h2>Index</h2>
#Model.getCount()
#foreach(var item in Model.Topics)
{
<div>#item.header</div>
}
Output:
Index
2
test
test2

Answer 5

It seems that you are not initializing your Topics anywhere in the code. If the collection is null it means it is not initialized. If you instantiate it with
ICollection<Topic> Topics = new List<Topic>();
Once initialized you should receive zero when calling Topics.Count. If you do not make a call to a database it will stay zero.
In your case check whether you are instantiating the Topics.