Help with navigating using Navigation Properties??? RSS

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  MangoMM

  Member

  65 Points

  55 Posts

  Help with navigating using Navigation Properties???

  Feb 22, 2012 09:11 PM|LINK

  Hi there,

  Just getting started with Visual Studio, .NET, C#, MVC3 etc so please go easy on me.

  Background:

  I am creating an MVC3 web application, SQL Server 2008, DB first with a generated model (emdx).

  I have followed tutorials (most go through Code first / Model first) and not DB first.

  I am doing it DB first as I am building an inventory control system with Bill of Materials functionality and Entity Framework seems not to support adjacency lists.

  My problem however is much more simple than the recursion.

  Problem:

  Table1: Categories

  CategoryId int, pk

  Name nvarchar(50)

  Navigation Properties : Parts 

   

  Table2: Parts

  PartId int, pk

  Name nvarchar(50)

  CategoryId int FK

   

  I am able to list ALL categories.

  I am able to list ALL parts.

  I am unable to list ALL parts which belong to a category.

   

   

  I have tried to implement this

   

  public ActionResult Browse(string genre)
   {
      // Retrieve Genre and its Associated Albums from database
      var genreModel = storeDB.Genres.Include("Albums")
          .Single(g => g.Name == genre);
   
      return View(genreModel);
   }

  from this tutorial http://www.asp.net/mvc/tutorials/mvc-music-store/mvc-music-store-part-4

  View:

  @model EM6.Models.Category
  
  @{
      ViewBag.Title = "Browse";
  }
  
  <h2>Browsing Category @Model.Name</h2>
  <ul>
  @foreach (var part in Model.Parts)
  {
      <li>@part.Name</li>
  }
  </ul>

  but I get the following error message.

   

  var categoryModel = _db.Categories.Include("Parts")
                  .Single(c => c.Name == myCategory);
  
  
  InvalidOperationException was unhandled by user code
  Sequence contains no elements

   

  Yes there is data in the database!

  Any help would be much appreciated.

   

  Thanks

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  ignatandrei

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  Re: Help with navigating using Navigation Properties???

  Feb 22, 2012 09:14 PM|LINK

  var categoryModel = _db.Categories.Include("Parts").Where(c => c.Name == myCategory).FirstOrDefault();
  if( categoryModel  == null)
  return Content(" does not exists category with name : " + myCategory)
  else
  return View(categoryModel ); // or what you have

  My .NET blog : http://msprogrammer.serviciipeweb.ro/ |2012 Programmer tools
• • Reply
  

  MangoMM

  Member

  65 Points

  55 Posts

  Re: Help with navigating using Navigation Properties???

  Feb 22, 2012 09:26 PM|LINK

  Thank you for the very quick reply.

   

  Now I am not getting the exception, but the view is not showing any Parts, just an empty Unordered list.

   

  Here is my Index view:

  @model IEnumerable<EM6.Models.Category>
  
  @{
      ViewBag.Title = "Categories";
  }
  
  <h2>Browse Categories</h2>
  
  <p>Select from @Model.Count() categories</p>
  
  <ul>
  @foreach (var category in Model) {
      
      <li>
                  @Html.ActionLink(
                  category.Name,
                  "Browse",
                  new { myCategory = category.Name }
              )
      </li>
  }
  </ul>

   

  Here is my Browse View:

  @model EM6.Models.Category
  
  @{
      ViewBag.Title = "Browse";
  }
  
  <h2>Browsing Category @Model.Name</h2>
  <ul>
  @foreach (var part in Model.Parts)
  {
      <li>@part.Name</li>
  }
  </ul>

   

   

   Here is a snippet of the generated HTML:

          <section id="main">
  
              
  
  
  
  <h2>Browsing Category Service Parts</h2>
  
  <ul>
  
  </ul>
  
          </section>
  
          <footer>
  
          </footer>
  

   

   

   

• • Reply
  

  ignatandrei

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  Re: Help with navigating using Navigation Properties???

  Feb 23, 2012 06:58 AM|LINK

  <h2>Browsing Category @Model.Name</h2>
  @if(Model.Parts == null ||Model.Parts.Count() == 0){
  <text> no parts in model</text>
  }
  
   <ul>
  @foreach (var part in Model.Parts)
  {
      <li>@part.Name</li>
  }
  </ul>

  My .NET blog : http://msprogrammer.serviciipeweb.ro/ |2012 Programmer tools
  • Marked as answer by MangoMM on Feb 23, 2012 08:56 AM
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  MangoMM

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  65 Points

  55 Posts

  Re: Help with navigating using Navigation Properties???

  Feb 23, 2012 08:57 AM|LINK

  Perfect. Works now. Not sure why, but it does. It is pulling in Model.Parts as it should. Thanks for your help.