Web API single string parameter validation using validation attributes

Question

I know that you can use Validation attributes on a model to validate it like so:

public class CommunicationQuery
{
    [RegularExpression("[0-9]{0,10}", ErrorMessage = "Please enter a valid policy number")]
    public string PolicyId { get; set; }
    [RegularExpression("[0-9]{0,10}", ErrorMessage = "Please enter a valid member number")]
    public string MemberId { get; set; }
}

public IEnumerable<Communication> Get([FromUri]CommunicationQuery documentQuery)
{

}

But is it possible to validate a single string using validation attributes such as this?

public async Task<HttpResponseMessage> Get([RegularExpression("[0-9]{0,10}")]string id)
{

}

This didn't seem to work. The only ways I've been able to do this was to either create a wrapper object and use [FromUri], use a custom ActionFilterAttribute on the action itself or to manually validate the parameter in the controller action using a regular expression.

Web API Route Constraints also useful for validation like [Route("XYZ/{id:int:maxlength(10)}")] — 111
– 111, Commented Feb 26, 2015 at 7:28

Yannick Meeus · Accepted Answer · 2015-03-02 22:48:23Z

6

If you're using Attribute Routing to manage your paths coming into your controllers, you can always do something like this:

[Route("{Id:regex([0-9]{0,10})}")]
public async Task<HttpResponseMessage> Get(string id)
{

}

There are various route contraints, as documented on the Attribute Routing overview documentation.

It does raise the question as to why you're accepting a numeric string of length 10 as your id. you'll have to be careful when parsing it into an int that it doesn't exceed 2,147,483,647, as that's the maximum size for a default integer.

edited Mar 2, 2015 at 22:48

answered Feb 26, 2015 at 9:01

Yannick Meeus

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Comments

Andrew M. · Accepted Answer · 2016-02-25 19:59:43Z

The other two solutions will only work for route attributes. However if you are wanting to validate a query parameter you could do something like this:

public class MinWithStatusAttribute : ParameterBindingAttribute 
{
    private readonly int _minValue;
    public MinWithStatusAttribute(int minValue)
    {
        _minValue = minValue;
    }

    public override HttpParameterBinding GetBinding(HttpParameterDescriptor parameter) => new MinWithStatusParameterBinding(parameter, _minValue);
}

public class MinWithStatusParameterBinding : HttpParameterBinding, IValueProviderParameterBinding
{
    private readonly int _minValue;
    public HttpParameterBinding DefaultUriBinding; 

    public MinWithStatusParameterBinding(HttpParameterDescriptor desc, int minValue)
        : base(desc)
    {
        _minValue = minValue;
        var defaultUrl = new FromUriAttribute();
        this.DefaultUriBinding = defaultUrl.GetBinding(desc);
        this.ValueProviderFactories = defaultUrl.GetValueProviderFactories(desc.Configuration);
    }


    public override Task ExecuteBindingAsync(ModelMetadataProvider metadataProvider, HttpActionContext actionContext, CancellationToken cancellationToken)
    {
        return DefaultUriBinding.ExecuteBindingAsync(metadataProvider, actionContext, cancellationToken).ContinueWith((tsk) =>
        {
            var currentBoundValue = this.GetValue(actionContext);
            if (!(currentBoundValue is int)) return; //if it is not an Int, return.
            var currentBoundInt = (int)currentBoundValue;
            if (currentBoundInt >= _minValue) return; //If the value provided is greater than or equal to the min value, return. Else throw an error
            var preconditionFailedResponse = actionContext.Request.CreateResponse(HttpStatusCode.PreconditionFailed, $"The parameter {DefaultUriBinding.Descriptor.ParameterName} must be greater than or equal to {_minValue}" });
            throw new HttpResponseException(preconditionFailedResponse);
        }, cancellationToken);
    }

    public IEnumerable<ValueProviderFactory> ValueProviderFactories { get; } //IValueProviderParameterBinding
}

This is for an integer, but you could easily modify it to work with string regex. Now it can be applied to your query parameter as such:

public IHttpActionResult SendEmailToCandidate(int id, [MinWithStatus(3)]int company_id, [MinWithStatus(3)]int recruiter_id, string subject, string body)
    {
        //Do stuff in your controller method. If they enter less than 3 it will display an error with Http status code 412 precondition failed.
    }

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