Web Api 2 Serialize data annotations - validation

Question

I have a domain object Owner. This has some data annotations which will be used in the web api post method to validate.
public class Owner
{
[Required(ErrorMessage ="Please select a title")]
public string Title { get; set; }
[Required(ErrorMessage = "First name is required")]
[MaxLength(100, ErrorMessage ="Too long")]
public string Firstname { get; set; }
[Required(ErrorMessage = "Last name is required")]
public string Lastname { get; set; }
public string PostalAddressStreet { get; set; }
public string PostalAddressSuburb { get; set; }
public string PostalAddressState { get; set; }
}
Now i need to send this object's validation rules (defined in data annotations) to the front end in a get request. I was looking at this question which explains how to do this in MVC. But couldnt get it to working in a web api Get method. This is what i tried.
[HttpGet]
[Route("GetOwnerDefinition")]
public string GetPetOwnerDefinition()
{
Owner owner = new Owner();
System.Web.Http.Metadata.Providers.DataAnnotationsModelMetadataProvider metaProvider = new System.Web.Http.Metadata.Providers.DataAnnotationsModelMetadataProvider();
var metaData = metaProvider.GetMetadataForProperty(null, typeof(Owner), "Firstname");
var validationRules = metaData.GetValidators(GlobalConfiguration.Configuration.Services.GetModelValidatorProviders());
foreach(System.Web.Http.Validation.Validators.DataAnnotationsModelValidator modelValidator in validationRules)
{
//need help here
}
At the end of the day i need to generate a JSON definition as below.
{"Firstname": "John",
"ValidationRules":[{"data-val-required":"This field is required.", "data-val-length-max":100}]}

Answer 1

Not sure whether it is the best way, this is what i have done. I have created a new instance of MVC context inside a web api method.
var mvcContext = new System.Web.Mvc.ControllerContext();
See the code below.
public Dictionary<string, string> GetValidationDefinition(object container, Type type)
{
var modelMetaData = System.Web.Mvc.ModelMetadataProviders.Current.GetMetadataForProperties(container, type);
var mvcContext = new System.Web.Mvc.ControllerContext();
var validationAttributes = new Dictionary<string, string>();
foreach (var metaDataForProperty in modelMetaData)
{
var validationRulesForProperty = metaDataForProperty.GetValidators(mvcContext).SelectMany(v => v.GetClientValidationRules());
foreach (System.Web.Mvc.ModelClientValidationRule rule in validationRulesForProperty)
{
string key = metaDataForProperty.PropertyName + "-" + rule.ValidationType;
validationAttributes.Add(key, System.Web.HttpUtility.HtmlEncode(rule.ErrorMessage ?? string.Empty));
key = key + "-";
foreach (KeyValuePair<string, object> pair in rule.ValidationParameters)
{
validationAttributes.Add(key + pair.Key, System.Web.HttpUtility.HtmlAttributeEncode(pair.Value != null ? Convert.ToString(pair.Value, System.Globalization.CultureInfo.InvariantCulture) : string.Empty));
}
}
}
return validationAttributes;
}