如何访问从 MVC 视图中的 ajax 调用调用的控制器返回的数据

Question

I have an MVC 5 view with the following JavaScript which is getting an error after invoking an action method on a controller:

<script type="text/javascript">
    $('#ddlvendors').change(function () {
                var descHtml = "";
                var vendorId = $(this).val(); 

                $.ajax(
                    {
                        type: "POST",
                        data: { vendorId: vendorId },
                        url: '@Url.Action("PurchaseOrderVendor")',
                        datatype: "json",
                        success: function (aVendorObject) {
                            alert(aVendorObject.Name);
                        },
                        error: function (req, status, error) {
                            alert(error);
                        }
                     });
            });
</script>

The controller action method is as follows:

[HttpPost]
public ActionResult PurchaseOrderVendor( int vendorId)
{
  Vendor aVendor=VendorServices.GetVendor(vendorId);

  return Json(aVendor);
}

The vendor object being returned is as follows:

 public class VendorViewModel
  {
    public int VendorId { get; set; }
    public string Name { get; set; }
    public string Address1 { get; set; }
    public string Address2 { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public string ZipCode { get; set; }
    public string Description { get; set; }
    public string ContactName { get; set; }
    public string Phone { get; set; }
  }

Using the Visual Studio 2017 debugger I can see the vendor data is correctly getting filled on the controller side. If I don't try to access any member data the ajax call completes without an error. However, when I try to access any part coming in as aVendorObject such as aVendorObject.Name I get a browser error saying "Internal Server Error". How can I fix my success handler in the ajax call so I can access members of the Vendor object being returned from the controller?

Thanks in advance.

Answer 1

The LazyLoading feature of EntityFramework 6 did not have the Vendor object available when it was needed. I added a line in the VendorServices class to turn off LazyLoading which fixed the problem. Below is the method where I turn off LazyLoading for this particular VendorService method:

 static public Vendor GetVendor(int aVendorId)
{
  Vendor vendor;
  using (RgmSiteDAL RgmSiteDALCtx = new RgmSiteDAL())
  {
    //** Now setting LazyLoadingEnabled to false.
    RgmSiteDALCtx.Configuration.LazyLoadingEnabled = false;

    vendor = RgmSiteDALCtx.Vendor
                .Where(v => v.VendorId == aVendorId)
               .FirstOrDefault<Vendor>();

  }
    return vendor;
}

I found out that I can also fix the problem if I include any navigation properties defined with the Vendor entity as in the following:

vendor = RgmSiteDALCtx.Vendor
                   .Where(v => v.VendorId == aVendorId)
                   .Include(v => v.PurchaseOrder) //because is in Vendor navigation property
                  .FirstOrDefault<Vendor>();

For my situation I will stick with the first solution which sets LazyLoadingEnabled to false. This is because the option to generate my entities from my existing database setup my PurchaseOrder table as a navigation property for my Vendor which I believe is incorrect. My Vendor object does not need anything from my PurchaseOrder entity when I query for Vendor information. I will look into removing the PurchaseOrder navigation property from my Vendor entity because I believe it was incorrectly setup by the create entities from database tool in Visual Studio.