Validation Error message in mvc3

Basically, by circumventing the MVC pattern you can't get what you are looking for without using javascript. This would work.

Put this next or under your input to show an error

@Html.Label("lblError", "")

<input type="submit" id="submitButton" value="Save Data" />

//Search By Entity Info
submitButton.onclick = function (event) {

    if(isNotEmpty(firstName)) {}; // for multiple fields, put them all into a separate call and return true only if they all are OK
    else {
        return false;
    }
}

//Validation Methods
function isNotEmpty(field) {
    var fieldData = field.value;
    if (fieldData == null || fieldData.length == 0 || fieldData == "") {
        field.className = "FieldError"; // this class "FieldError" would need to use styling CSS to give the field the look that it was in error
        var errorMessage = document.getElementById("lblError");
        errorMessage.Value = "Error - Your custom text here";
        return false;
    } 
}

This is just an example and would need tweaked

But I would advise strongly FOR using ViewModels. You might as well be using straight HTML rather than the MVC 3 framework. You're doing yourself a disservice by not using MVC the way it is meant to be used.

Look at the amount of code I had to write! And ViewModels provide client side as well as server side validation. So you don't get burned just because you only relied on client side and someone either sent invalid data thru or went around it by posting data directly thru the URL and pushing bad data into your DB

Why would you not want to use data annotations?

Relying only upon client side validation is not a good idea as a user could have javascript disabled within their browser, be using an older browser in the case of HTML5 form validation. This only leads to a user submitting invalid form data. You should always use a combination of client / server side validation.

I would strongly recommend you create a view model and enable data annotations. For example note, the usage of the required attribute and a custom email attribute for your validation purposes:

[Required(ErrorMessage = "Please enter email address"]
[Email(ErrorMessage = "Please enter valid email")]
public string Email { get; set; }

An example email validation attribute:

public class EmailAttribute : RegularExpressionAttribute
{
    private const string EmailReg = @"^(?("")("".+?""@)|(([0-9a-zA-Z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-zA-Z])@))(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,6}))$";

    public EmailAttribute() : base(EmailReg)
    {
    }
}

Now, as per your question if you want to use only client side validation then you should definitely not rely upon HTML5 form validation. A quick way of enabling validation would be to get the jquery validation plugin.

Demo here: http://jquery.bassistance.de/validate/demo/