How to serialize a model with all validation attributes from the individual properties?

Question

Context: creating a jsonP service with mvc controller methods which provides a definition of formfields including all validation rules.

My problem is that I do not know how to serialize the validation attributes. I prefer the validation attributes in the same format as they are serialized by Razor when using unobtrusive validation in regular Mvc views.

For serializing to json I use NewtonSoft.Json (4.0.2).

Example of model: public class Profile{

    [Required(ErrorMessage="This field is required.")]
    [StringLength(25, ErrorMessage="Max 25 chars.")]
    public string Firstname{get;set;}
    }

Example of preferred serialized javascript:

     {"Firstname": "John", 
      "ValidationRules":[{"data-val-required":"This field is required.", "data-val-length-max":25, "data-val-length":"Max 25 chars." }]}

Any help or pointers are very much appreciated.

Answer 1

This will construct a dictionary with the validation attributes for a given property based on the data annotation attributes:

var metadata = ModelMetadataProviders.Current.GetMetadataForProperty(null, typeof(MyModel), "MyProperty");
var validationRules = metadata.GetValidators(ControllerContext).SelectMany(v => v.GetClientValidationRules());
var validationAttributes = new Dictionary<string, string>();

foreach (ModelClientValidationRule rule in validationRules)
{
    string key = "data-val-" + rule.ValidationType;
    validationAttributes.Add(key, HttpUtility.HtmlEncode(rule.ErrorMessage ?? string.Empty));
    key = key + "-";
    foreach (KeyValuePair<string, object> pair in rule.ValidationParameters)
    {
        validationAttributes.Add(key + pair.Key,
            HttpUtility.HtmlAttributeEncode(
                pair.Value != null ? Convert.ToString(pair.Value, CultureInfo.InvariantCulture) : string.Empty));
    }
}

You should then serialize the validationAttributes dictionary with your property in your custom JSON serialization code.

Answer 2

This probably didn't exist at the time of this question, but there's now an updated way of doing getting the validation as a dictionary:

@Html.GetUnobtrusiveValidationAttributes("FieldName")

https://msdn.microsoft.com/en-us/library/system.web.mvc.htmlhelper.getunobtrusivevalidationattributes(v=vs.108).aspx

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UPDATE: I am having trouble with it returning an empty set for some fields when there should be validation, so I've actually gone with the accepted solution.