Question

I am having trouble performing data type validation which is dependent on another field. Most of the examples I found here are for making a field required or not based on a value of another field (MaidenName will be required only if IsMarried is true).

My Model

public class AttributeValuesModel
{
    public IList<AttributeModel> Values {get; set;}
}

public class AttributeModel
{
    [Required]
    public string AttributeName {get; set;}

    [Required]
    public string AttributeValue {get; set;}

    [Required]
    public int DataTypeId {get; set;}
}

What I would like to do is to validate the user input for AttributeValue based on the value of DataTypeId. For clarity, the value of DataTypeId is known before I even show the view to the user.

    //Possible values for DataTypeId are 
    //1 for decimal
    //2 for dates
    //3 for integer

Is this possible?

Answer 1

It’s not so hard to roll your own validation attribute. I have implemented one some time ago. It checks whether value of other property is smaller than property that is decorated with this attribiute:

[AttributeUsage(AttributeTargets.Property, AllowMultiple = true, Inherited=true)]
public class SmallerThanAttribute : ValidationAttribute
{
    public SmallerThanAttribute(string otherPropertyName)
    {
        this.OtherPropertyName = otherPropertyName;
    }

    public string OtherPropertyName { get; set; }
    public string OtherPropertyDisplayName { get; set; }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        return IsValid(OtherPropertyName, value, validationContext);
    }

    private ValidationResult IsValid(string otherProperty, object value, ValidationContext validationContext)
    {
        PropertyInfo otherPropertyInfo = validationContext.ObjectType.GetProperty(otherProperty);

        if (otherPropertyInfo == null)
        {
            throw new Exception("Could not find property: " + otherProperty);
        }

        var displayAttribute = otherPropertyInfo.GetCustomAttributes(typeof(DisplayAttribute), true).FirstOrDefault() as DisplayAttribute;

        if (displayAttribute != null && OtherPropertyDisplayName == null)
        {
            OtherPropertyDisplayName = displayAttribute.GetName();
        }

        object otherPropertyValue = otherPropertyInfo.GetValue(validationContext.ObjectInstance, null);

        var smaller = (IComparable) value;
        var bigger = (IComparable) otherPropertyValue;

        if (smaller == null || bigger == null)
        {
            return null;
        }

        if (smaller.CompareTo(bigger) > 0)
        {
            return new ValidationResult(string.Format(ValidatorResource.SmallerThan, validationContext.DisplayName, OtherPropertyDisplayName));
        }

        return null;
    }
}

There is one gotcha. Error message format is defined in resource class property (ValidatorResource.SmallerThan), so it’s not pluggable — I didn’t need this. However, I think it still could be a good starting point for you.