Entity Framework

Question

I'm doing MVC 3 Web Application and have weird problem. Here is some code:

Model declaration:

public class Project
{
    public int ID { get; set; }

    [Required(ErrorMessage = "Write a title.")]
    public string Title { get; set; }

    public DateTime TimeAdded { get; set; }

    [Required(ErrorMessage = "Write some description.")]
    [MaxLength(int.MaxValue)]
    public string Content { get; set; }

    public ICollection<Comment> Comments { get; set; }
}   

public class Comment
{
    public int ID { get; set; }

    [Required()]
    public int ProjectID { get; set; }

    public DateTime TimeAdded { get; set; }

    [Required()]
    public string Text { get; set; }

    public Project project { get; set; }
}

Controller:

public class HomeController : Controller
{
    dataDBContext db = new dataDBContext();

    //
    // GET: /Home

    public ActionResult Index()
    {
        var comments = from c in db.Comments
                       select c;

        var projects = from p in db.Projects
                       orderby p.TimeAdded descending
                       select p;

        return View(projects.ToList());
    }

When I run project Comments are not visible on my view.
I'm setting a breakpoint just after both linq queries, debugging and checking "project" variable fields Comments, they are not populated. Then I'm checking "comments" variable, it has some data. Again checking "project" variable and SOMEHOW fields Comments are populated and finally Comments appears on website. If I won't set breakpoint and check if variable "comments" is populated they won't appear on website. (I hope this is understandable)

I found simple workaround:

public ActionResult Index()
{
    var projects = from p in db.Projects
                   orderby p.TimeAdded descending
                   select p;

    foreach (var p in projects)
    {
        var comments = from c in db.Comments
                       where c.ProjectID == p.ID
                       select c;


        p.Comments = comments.ToList();
    }

    return View(projects.ToList());
}

but it looks (according to point 2) that this can be automatically populated SOMEHOW :)

Is there any way to do it?

Another tries based on given answers:

public class HomeController : Controller
{
    dataDBContext db;

    public HomeController()
    {
        db = new dataDBContext();
        db.Configuration.LazyLoadingEnabled = false;
    }

    //
    // GET: /Home

    public ActionResult Index()
    {
        var projects = from p in db.Projects
                       orderby p.TimeAdded descending
                       select p;

        return View(projects.ToList());
    }

I have foreign key. I added LazyLoadingEnabled. There is project.ToList() and it doesn't work.

Based on second answer I have done something like that:

public class HomeController : Controller
{
    dataDBContext db;

    public HomeController()
    {
        db = new dataDBContext();
    }

    //
    // GET: /Home

    public ActionResult Index()
    {
        var projects = from p in db.Projects
                       orderby p.TimeAdded descending
                       select p;

        var comments = from c in db.Comments
                       select c;

        List<Comment> l = comments.ToList();

        return View(projects.ToList());
    }

I have added just comments.ToList() and it is working. But I'm not sure if it is right solution. Probably better than my workaround (point 3). Any suggestions?

Thanks

You should really consider a separation of concerns, you have too much going on in your controller. Create a repository with methods that return your data and move that out of the controller. Try checking out some docs on MVC best practices to get you headed in the right direction. — Jason Yost
– Jason Yost, Commented Mar 7, 2011 at 6:30
Because for every project you pull the comments, which given you N Select statements for N projects + 1 (a.k.a. Select N+1) for the project itself. This is quite inefficient and should be avoided. — flq
– flq, Commented Mar 7, 2011 at 18:13

Nico · Accepted Answer · 2011-03-06 18:19:57Z

5

If you have a foreign key between Comments and Projects you can do something like this

db.ContextOptions.LazyLoadingEnabled = false;
var projects = from p in db.Projects.Include("Comments")
                       orderby p.TimeAdded descending
                       select p;

It will load all comments for all projects when you will execute the .ToList(). You'll be able to access the data by the navigate property "Comments" of the project object.

answered Mar 6, 2011 at 18:19

Nico

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2 Comments

A_lan Over a year ago

I probably doing something wrong but it's not working. I'm sure that have foreign key. I added db.Confiburation.LazyLoadingEnabled = false. I perform ToList() on projects and there is no data.

Nico Over a year ago

Have you set the Include("Comments") in the linq ? Have you import foreign key into EDMX file ? Have you define a navigate property from projects to comments (EDMX property while importing from database) ?

Brian Kretzler · Accepted Answer · 2011-03-06 18:11:51Z

0

When you are stopped at a breakpoint and examine the query results, you are effectivly triggering the "ToList" execution, so your new code is performing the same automatic population as your debug session.

answered Mar 6, 2011 at 18:11

Brian Kretzler

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1 Comment

A_lan Over a year ago

I have added just comments.ToList() and it is working. But I'm not sure if it is right solution.

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