How can we do validations in MVC?

Answer

One of the easiest ways of doing validation in MVC is by using data annotations. Data annotations are nothing but attributes which can be applied on model properties. For example, in the below code snippet we have a simple Customer class with a property customercode.

This CustomerCode property is tagged with a Required data annotation attribute. In other words if this model is not provided customer code, it will not accept it.

public class Customer
{
    [Required(ErrorMessage="Customer code is required")]
    public string CustomerCode
    {
        set;
        get;
    } 
}  

In order to display the validation error message we need to use the ValidateMessageFor method which belongs to the Html helper class.

<% using (Html.BeginForm("PostCustomer", "Home", FormMethod.Post))
{ %>
<%=Html.TextBoxFor(m => m.CustomerCode)%>
<%=Html.ValidationMessageFor(m => m.CustomerCode)%>
<input type="submit" value="Submit customer data" />
<%}%> 

Later in the controller we can check if the model is proper or not by using the ModelState.IsValid property and accordingly we can take actions.

public ActionResult PostCustomer(Customer obj)
{
    if (ModelState.IsValid)
    {
        obj.Save();
        return View("Thanks");
    }
    else
    {
        return View("Customer");
    }
}

Below is a simple view of how the error message is displayed on the view.