MVC validation for unique - asp.net-mvc

Question

Hi I have an MVC app that I used to insert update invoices:
public class Invoice : IEntity, IValidatableObject
{
public virtual int InvoiceId { get; set; }
[Required(ErrorMessage = "Invoice Number is a required field.")]
[Column(TypeName = "varchar")]
[StringLength(20)]
[Display(Name = "Invoice Number:")]
public virtual string InvoiceNumber { get; set; }
[Required(ErrorMessage = "Organisation is a required field.")]
[Display(Name = "Organisation:")]
public int OrganisationId { get; set; }
...
}
The problem is I have a requirement "The combination of organisation and invoice number must be unique.
So this has been set up by the DBA in the database. So if I try to do this it will return an exception.
Is there a way instead of displaying the exception to catch it and add a custom error message to the validation summary?

Answer 1

You could catch the exception and add the error to the model state so that your client code handles all errors the same way. Something like:
ModelState.AddModelError("InvoiceNumber", "The combination of organisation and invoice number must be unique.");

Answer 2

you can achieve this by putting remote attribute on both properties and in AdditionalField parameter you pass the name of other property like
[Remote("IsUnique","home",AdditionalFields = "OrganisationID",ErrorMessage = "abc")]
virtual string InvoiceNumber { get; set; }
[Required(ErrorMessage = "Organisation is a required field.")]
[Display(Name = "Organisation:")]
[Remote("IsUnique","home",AdditionalFields = "InvoiceNumber",ErrorMessage = "abc")]
public int OrganisationId { get; set; }
and you can write InUnique method in home controller (for instance) like
public JsonResult IsUnique(string InvoiceNumber, int? OrganisationID)
{
if(InvoiceNumber == null || !Organisation.HasValue)
{
return Json({valid = true});//null check is not job of this attribute
}
else
{
bool result = CheckDbForUniqueness(InvoiceNumber, OrganisationID.Value);
return Json({valid = result});
}
}
This method will be invoked when you change value of either inputs on the form and take the other value as parameter. if either value is null it would return true and null checking will be handled by Required attributes.

Answer 3

Without getting fancy...you could catch it in the controller, then display the message in the view via a member of the model or ViewBag/ViewData.

Answer 4

You can also write a custom validator that checks this for you (even with some client-side validation as well). I wrote one that checked a database for whether a username existed or not, a similar check could be done for this, without relying on exceptions (although you still would want to handle it I wouldn't recommend using exceptions for a normal course of action).