ASP.NET code snippit to query database for unique field value - asp.net

Question

I'm trying to create custom remote data annotation to check for unique values.
So far I have:
[Remote("checkForUniqueSpeciesName", "Create", ErrorMessage = "A Species by that name already exists.")]
public string SpeciesName { get; set; }
and
public ActionResult checkForUniqueSpeciesName(string species_name)
{
bool is_unique = ........
return Json(is_unique, JsonRequestBehavior.AllowGet);
}
To be honest, I don't really understand how this works, I'm just trying to follow examples found on the web. I guess checkForUniqueSpeciesName is called when the form is submitted, and the method returns true or false. Is there something I need to put in the view to make the validation message come up, such as?
#Html.ValidationMessageFor(model => model.SpeciesName, "", new { #class = "text-danger" })
Do I need that?
Model Species.cs:
public class Species
{
[Key]
public int SpeciesId { get; set; }
[Display(Name = "Species")]
[Required(ErrorMessage = "You must enter a species name.")]
[Remote("CheckForUniqueSpeciesName", "Create", ErrorMessage = "A Species by that name already exists.")]
public string SpeciesName { get; set; }
}
Controller SpeciesController.cs:
namespace Gators3.Controllers
{
public class SpeciesController : Controller
{
private GatorsContext db = new GatorsContext();
// GET: Species
public ActionResult Index()
{
return View(db.Species.ToList());
}
// GET: Species/Create
public ActionResult Create()
{
return View();
}
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create([Bind(Include = "SpeciesId,SpeciesName")] Species species)
{
if (ModelState.IsValid)
{
db.Species.Add(species);
db.SaveChanges();
return RedirectToAction("Index");
}
return View(species);
}
public ActionResult CheckForUniqueSpeciesName(string speciesName)
{
using (GatorsContext ctx = new GatorsContext())
{
bool isUnique = !ctx.Species.Any(s => s.SpeciesName == speciesName);
return Json(isUnique, JsonRequestBehavior.AllowGet);
}
}
.
.
.
.
View Views->Species->Create.cshtml:
#model Gators3.Models.Species
#{
ViewBag.Title = "Create";
}
<h2>Create</h2>
#using (Html.BeginForm())
{
#Html.AntiForgeryToken()
<div class="form-horizontal">
<h4>Species</h4>
<hr />
#Html.ValidationSummary(true, "", new { #class = "text-danger" })
<div class="form-group">
#Html.LabelFor(model => model.SpeciesName, htmlAttributes: new { #class = "control-label col-md-2" })
<div class="col-md-10">
#Html.EditorFor(model => model.SpeciesName, new { htmlAttributes = new { #class = "form-control" } })
#Html.ValidationMessageFor(model => model.SpeciesName, "", new { #class = "text-danger" })
</div>
</div>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<input type="submit" value="Create" class="btn btn-default" />
</div>
</div>
</div>
}
<div>
#Html.ActionLink("Back to List", "Index")
</div>
#section Scripts {
#Scripts.Render("~/bundles/jqueryval")
}

Answer 1

I guess checkForUniqueSpeciesName is called when the form is
submitted, and the method returns true or false.
No, that is not the case. The [RemoteAttribute] adds some JavaScript to your page automatically that will call a method on your Controller to do some server side validation and display the result on the page without the user needing to submit the whole HTML form. i.e. The validation is invoked when you tab out of the text box, not when you click submit.
With your code, I assume your controller is named CreateController?
I'm guessing you're just missing your data access code to actually check uniqueness?
So something like this would be required:
public ActionResult CheckForUniqueSpeciesName(string speciesName)
{
using (YourEntityFrameworkDbContext ctx = new YourEntityFrameworkDbContext())
{
bool isUnique = !ctx.Species.Any(s => s.SpeciesName == speciesName);
return Json(isUnique , JsonRequestBehavior.AllowGet);
}
}
Then in your view, you just need something like this:
#Html.ValidationMessageFor(x => x.SpeciesName)
Which will display the validation message you specified in your [Remote] attribute.
By the way, just as a side note - the coding conventions/casing you've applied to some of your code won't be popular with most C# programmers (unless your team are abiding by an unusual standard) so note the formatting I've applied.
Update - I think your code needs to have the following:
[Remote("CheckForUniqueSpeciesName", "Species", ErrorMessage="A Species by that name already exists.")]