ASP.NET MVC Conditional validation

Question

How to use data annotations to do a conditional validation on model?

For example, lets say we have the following model (Person and Senior):

public class Person
{
    [Required(ErrorMessage = "*")]
    public string Name
    {
        get;
        set;
    }

    public bool IsSenior
    {
        get;
        set;
    }

    public Senior Senior
    {
        get;
        set;
    }
}

public class Senior
{
    [Required(ErrorMessage = "*")]//this should be conditional validation, based on the "IsSenior" value
    public string Description
    {
        get;
        set;
    }
}

And the following view:

<%= Html.EditorFor(m => m.Name)%>
<%= Html.ValidationMessageFor(m => m.Name)%>

<%= Html.CheckBoxFor(m => m.IsSenior)%>
<%= Html.ValidationMessageFor(m => m.IsSenior)%>

<%= Html.CheckBoxFor(m => m.Senior.Description)%>
<%= Html.ValidationMessageFor(m => m.Senior.Description)%>

I would like to be the "Senior.Description" property conditional required field based on the selection of the "IsSenior" propery (true -> required). How to implement conditional validation in ASP.NET MVC 2 with data annotations?

Answer 1

I have solved this by handling the "ModelState" dictionary, which is contained by the controller. The ModelState dictionary includes all the members that have to be validated.

Here is the solution:

If you need to implement a conditional validation based on some field (e.g. if A=true, then B is required), while maintaining property level error messaging (this is not true for the custom validators that are on object level) you can achieve this by handling "ModelState", by simply removing unwanted validations from it.

...In some class...

public bool PropertyThatRequiredAnotherFieldToBeFilled
{
  get;
  set;
}

[Required(ErrorMessage = "*")] 
public string DepentedProperty
{
  get;
  set;
}

...class continues...

...In some controller action ...

if (!PropertyThatRequiredAnotherFieldToBeFilled)
{
   this.ModelState.Remove("DepentedProperty");
}

...

With this we achieve conditional validation, while leaving everything else the same.

---

UPDATE:

This is my final implementation: I have used an interface on the model and the action attribute that validates the model which implements the said interface. Interface prescribes the Validate(ModelStateDictionary modelState) method. The attribute on action just calls the Validate(modelState) on IValidatorSomething.

I did not want to complicate this answer, so I did not mention the final implementation details (which, at the end, matter in production code).

Answer 2

There is now a framework that does this conditional validation (among other handy data annotation validations) out of the box: http://foolproof.codeplex.com/

Specifically, take a look at the [RequiredIfTrue("IsSenior")] validator. You put that directly on the property you want to validate, so you get the desired behavior of the validation error being associated to the "Senior" property.

It is available as a NuGet package.

Answer 3

You can disable validators conditionally by removing errors from ModelState:

ModelState["DependentProperty"].Errors.Clear();

Answer 4

You need to validate at Person level, not on Senior level, or Senior must have a reference to its parent Person. It seems to me that you need a self validation mechanism that defines the validation on the Person and not on one of its properties. I'm not sure, but I don't think DataAnnotations supports this out of the box. What you can do create your own Attribute that derives from ValidationAttribute that can be decorated on class level and next create a custom validator that also allows those class-level validators to run.

I know Validation Application Block supports self-validation out-of the box, but VAB has a pretty steep learning curve. Nevertheless, here's an example using VAB:

[HasSelfValidation]
public class Person
{
    public string Name { get; set; }
    public bool IsSenior { get; set; }
    public Senior Senior { get; set; }

    [SelfValidation]
    public void ValidateRange(ValidationResults results)
    {
        if (this.IsSenior && this.Senior != null && 
            string.IsNullOrEmpty(this.Senior.Description))
        {
            results.AddResult(new ValidationResult(
                "A senior description is required", 
                this, "", "", null));
        }
    }
}

Answer 5

I'm using MVC 5 but you could try something like this:

public DateTime JobStart { get; set; }

[AssertThat("StartDate >= JobStart", ErrorMessage = "Time Manager may not begin before job start date")]
[DisplayName("Start Date")]
[Required]
public DateTime? StartDate { get; set; }

In your case you would say something like "IsSenior == true". Then you just need to check the validation on your post action.

Answer 6

Thanks Merritt :)

I've just updated this to MVC 3 in case anyone finds it useful; http://blogs.msdn.com/b/simonince/archive/2011/02/04/conditional-validation-in-asp-net-mvc-3.aspx

Simon