Return a list of errors with BadRequest (WebApi)

Question

As the title indicates all I'm trying to do is return a custom collection of errors if the "Model" is incomplete.

Whilst actively "SO'ing/Googling" I haven't found a solution to help with my problem.

I could of used "ModelState" but due to "Customisation", I'd like to do this manually.

Code as Follows:

API Level

// POST api/<controller>
[HttpPost]
[Route("")]
public async Task<IHttpActionResult> Post([FromBody]Order order)
{
    var modelResponse = new ModelResponse<Order>(order);
    if (order == null)
        return BadRequest("Unusable resource, object instance required.");

    //Check if all required properties contain values, if not, return response
    //with the details
    if (!modelResponse.IsModelValid())
        return this.PropertiesRequired(modelResponse.ModelErrors());

    try
    {
        await _orderService.AddAsync(order);
    }
    catch (System.Exception ex)
    {
        return InternalServerError();
    }
    finally
    {
        _orderService.Dispose();
    }

    return Ok("Order Successfully Processed.");
}

Properties Required Action Result

public List<string> Messages { get; private set; }
public HttpRequestMessage Request { get; private set; }

public PropertiesRequiredActionResult(List<string> message, 
    HttpRequestMessage request)
{
    this.Messages = message;
    this.Request = request;
}
public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
{
    return Task.FromResult(Execute());
}

public HttpResponseMessage Execute()
{
    HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.BadRequest);
    response.Content = new ObjectContent()
        //new List<StringContent>(Messages); //Stuck here
    response.RequestMessage = Request;
    return response;
}

Finding incomplete properties, based on a custom Attribute

private T _obj;

public ModelResponse(T obj)
{
    _obj = obj;
}

private Dictionary<string, object> GetPropertyAttributes(PropertyInfo property)
{
    Dictionary<string, object> attribs = new Dictionary<string, object>();
    // look for attributes that takes one constructor argument
    foreach (CustomAttributeData attribData in property.GetCustomAttributesData())
    {

        if (attribData.ConstructorArguments.Count == 1)
        {
            string typeName = attribData.Constructor.DeclaringType.Name;
            if (typeName.EndsWith("Attribute")) typeName = typeName.Substring(0, typeName.Length - 9);
            attribs[typeName] = attribData.ConstructorArguments[0].Value;
        }

    }
    return attribs;
}
private IEnumerable<PropertyInfo> GetProperties()
{
    var props = typeof(T).GetProperties().Where(
            prop => Attribute.IsDefined(prop, typeof(APIAttribute)));

    return props;
}
public bool IsModelValid()
{
    var props = GetProperties();
    return props.Any(p => p != null);
}
public List<string> ModelErrors()
{
        List<string> errors = new List<string>();
        foreach (var p in GetProperties())
        {

            object propertyValue = _obj.GetType()
                .GetProperty(p.Name).GetValue(_obj, null);

            if (propertyValue == null)
            {
                errors.Add(p.Name + " - " + GetPropertyAttributes(p).FirstOrDefault());
            }
        }
        return errors;
}

Sample of Attribute

/// <summary>
/// The date and time when the order was created.
/// </summary>
[API(Required = "Order Created At Required")]
public DateTime Order_Created_At { get; set; }

So ignoring the two latter snippets, that was more to give a full process overview. I completely understand there are a few "out the box" techniques but I do enjoy crafting my own implementations.

To the point, Is it possible to return a list of errors with "BadRequest"?

Much appreciated.

Answer 1

You probably looking for using this method:

BadRequestObjectResult BadRequest(ModelStateDictionary modelState)

The usage of it is something like this, the example is from another question here in SO :

if (!ModelState.IsValid)
     return BadRequest(ModelState);

Depending on the model errors, you get this result:

{
   Message: "The request is invalid."
   ModelState: {
       model.PropertyA: [
            "The PropertyA field is required."
       ],
       model.PropertyB: [
             "The PropertyB field is required."
       ]
   }
}

Hope it helps

Answer 2

In your custom implementation of IHttpActionResult use the request to create the response and pass the model and status code.

public List<string> Messages { get; private set; }
public HttpRequestMessage Request { get; private set; }

public HttpResponseMessage Execute() {
    var response = Request.CreateResponse(HttpStatusCode.BadRequest, Messages);
    return response;
}