WCF error handling using DataAnnotations Validator

ParameterInspector can also be used to validate DataMember in the data contract for the incoming request by using DataAnnotations Validator.

So suppose I have a DataContract defined something like this

 [DataContract]
    public class CompositeType
    {
        string stringValue = "Hello ";
        [DataMember]
        [Required(ErrorMessage = "Name is required")]
        [StringLength(20, MinimumLength = 1, ErrorMessage = "Name must have between 1 and 20 characters")]
        public string StringValue
        {
            get { return stringValue; }
            set { stringValue = value; }
        }
    }

Refer to DataAnnotations Required and StringLength attribute. Now I want a generic Validator which inspects the parameter and does Validation using DataAnnotations.

 
 public class ValidatingParameterInspector : IParameterInspector
    {
        public void AfterCall(string operationName, object[] outputs, object returnValue, object correlationState){}
  
        public object BeforeCall(string operationName, object[] inputs)
        {
   //So I loop through all the input parameters and validate it using DataAnnotations Validator
            foreach (var input in inputs)
            {
                if (input != null)
                {
                    ValidationContext context = new ValidationContext(input, null, null);
                    Validator.ValidateObject(input, context, true);
                }
            }
            return null;
        }
    }

And now you can add this to OperationBehavior or even endpoint behavior

 

 public class ValidatingParameterInspectorOperationBehavior : Attribute, IOperationBehavior
    {
        public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation){}
        public void AddBindingParameters(OperationDescription operationDescription, BindingParameterCollection bindingParameters){}
        public void Validate(OperationDescription operationDescription){}
        public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation)
        {
            ValidatingParameterInspector validatingParameterInspector = new ValidatingParameterInspector();
            dispatchOperation.ParameterInspectors.Add(validatingParameterInspector);
        }
    } 

So now before call reaches to the operation it will be inspected by BeforeCall where it will fail validation and raise exception. You can also raise custom FaultException