set dynamic data annotation error message from controller in asp.net mvc

Question

I am creating asp.net mvc application in which I storing my error messages in my database, now I want to use required field annotation instead of custom js validations when user clicks submit, my models looks like below,

[Required(ErrorMessage = "static error message")]
public string AttributeValue { get; set; }

I want to add dynamic error message instead of -> (static error message)

is there a way to add dynamic error message from controller.

For best performance do not hit the database every time you need to read a single text. Better build your own Resource file for dyanamic error message. — Mannan Bahelim
– Mannan Bahelim, Commented May 14, 2019 at 9:41
On validation failed you can add ModelState.AddModelError("AttributeValue", "error message"); to controller — Mannan Bahelim
– Mannan Bahelim, Commented May 14, 2019 at 9:49
@MannanBahelim yes I know that but I want to add error message during HTTPGet and not post — Ibrahim Shaikh
– Ibrahim Shaikh, Commented May 14, 2019 at 9:50

halfer · Accepted Answer · 2020-04-25 18:14:23Z

I had a requirement to set a regex expression dynamically, instead of creating my own validators as @Golda suggested in the comments, I cheated and just set the data-val errors using properties on my model, this is all the required attribute does anywhere with the help of a TagHelper.

Build your model as usual and add an additional property to hold the error message

[Required(ErrorMessage = "static error message")] // Leave this here for server side
public string AttributeValue { get; set; }

public string AttributeValueRequiredErrorMessage { get; set; }

In the controller make sure you set this property

 public async Task<IActionResult> SomeAction()
 {
      .... // other logic
      var  attributeValueRequiredErrorMessage  = callTheDb();

      var model = new Model()
      {
            AttributeValueRequiredErrorMessage = attributeValueRequiredErrorMessage
      }

      return View(model);  
 }

Then in your view simply do this

<input asp-for="AttributeValue " data-val-required="@Model.AttributeValueRequiredErrorMessage " />

This would work for a quick win but I would probably look at an alternative if you were doing this in multiple places.

If you dont mind taking the hit server side, you could also implement the [Remote] attribute if you're in dotnet core, see docs: https://learn.microsoft.com/en-us/aspnet/core/mvc/models/validation?view=aspnetcore-3.0#remote-attribute

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