How to return different types of model from a WebAPI controller action?

Question

I have a controller like this

    [ResponseType(typeof(List<InboxPatientModel>))]
    [Route("~/api/Messages/search")]
    public IHttpActionResult GetSearch(string serchTerm = "", string messageFor = "p")
    {
        try
        {
            if(messageFor == "p")
            {
                var inboxMessages = MessageToPatientList.Get(serchTerm);
                return Ok(inboxMessages);
            }
            else
            {
                var outboxMessages = MessageToDoctorList.Get(serchTerm);
                return Ok(outboxMessages);
            }
        }
        catch (Exception ex)
        {
             //some code for exception handling....
        }
    }

Here MessageToPatientList.Get and MessageToDoctorList.Get return list of different types say InboxPatientModel and InboxDoctorModel.

Is it possible to decorate the action with [ResponseType(...)] so that it can be dynamic and different types of list can be returned?

Answer 1

You could merge the different types of lists;

public class PatientModel
{
    public List<InboxPatientModel> Patients { get; set; }

    public List<InboxDoctorModel> Doctors { get; set; }
}

[ResponseType(typeof(PatientModel))]
[Route("~/api/Messages/search")]
public IHttpActionResult GetSearch(string serchTerm = "", string messageFor = "p")
{
    try
    {
        var patientModel = new PatientModel();
        if (messageFor == "p")
        {
            var inboxMessages = MessageToPatientList.Get(serchTerm);
            patientModel.Patients = inboxMessages;
        }
        else
        {
            var outboxMessages = MessageToDoctorList.Get(serchTerm);
            patientModel.Doctors = inboxMessages;
        }
        return Ok(patientModel);
    }
    catch (Exception ex)
    {
        //some code for exception handling....
    }
}

Answer 2

Your code will run just fine. The [ResponseType] attribute is only used to give hints for the Web API documentation page and tools like Swagger.

While the attribute has AllowMultiple=true in its AttributeUsage attribute, I don't think those documentation tools support this.

And they shouldn't. Returning different types from an API depending on the size of the moon, the day of the week or the value of some parameters is a hell to implement, a hell to document and a hell to consume.

Instead consider reviewing the design. Why should the actual type of a message change depending on who is the recipient? What is different between the two types of messages?

On the contrary, find properties they share. Then extract a base class, say, Message, and decorate the method with an attribute [ResponseType(typeof(Message))].