I've got an interface for requests and an interface for responses. I want to call something like this
public IResponse Get(IRequest req)
The request object is serialized and sent out on a bus.
I get a response back but I need to deserialize the response into the IResponse class that corresponds with the specific IRequest class. What's the right way to tie a response to a request so that whenever someone implements one of these request/response pairs they have to constrain it to a certain type?
Here's what I've tried:
public interface IRequest<T> where T : IResponse
{
Type GetResponseType(T t);
}
public interface IResponse { }
public class Res : IResponse
{
public string response { get; set; }
}
public class Req : IRequest<Res>
{
public string request { get; set; }
public Type GetResponseType(Res t)
{
return t.GetType();
}
}
The problem is, I don't know how to pass in an IRequest now:
public IResponse Get(IRequest req)
I get the error:
Using the generic type 'IRequest' requires 1 types argument
I tried:
public IResponse Get(IRequest<IResponse> req)
But when I try to pass in my class I get:
Argument 1: cannot convert from 'Req' to 'IRequest<(IResponse)>'
Does anyone know the proper way to do something like this, or at least let me know how to get my class to work as a parameter?
You could construct your method like that:
public IResponse Get<T>(IRequest<T> req) where T : IResponse
Regarding the signature, I'd use what Pawel suggests:
public IResponse Get<T>(IRequest<T> req) where T : IResponse
Regarding the implementation - do you really need a parameter for the GetResponseType) method? I ask because it seems like GetResponseType is tied to the generic type T and can always be inferred from it. The code below illustrates the point I am trying to make.
public interface IRequest<T> where T : IResponse
{
Type GetResponseType();
}
public interface IResponse { }
public class Res : IResponse
{
public string response { get; set; }
}
public class Req : IRequest<Res>
{
public string request { get; set; }
public Type GetResponseType()
{
return typeof(Res);
}
}
Related
I am working on writing a client library for reading from an MQTT API (that I have no control over).
For making requests I have a helper Request class that has all the default request parameters that always need to be provided. Each request has a payload property. I implemented this by making the Request class a generic class like: public class Request<T> where T : IRequestPayload and that has worked great, with one exception, when the request payload is only a string. Since string doesn't implement IRequestPayload, I cant make a Request with a payload of type string.
While looking into ways to handle this I wondered if it would be possible to flatten a derived Request class's Value property and save it to Payload. An example of what I mean is below:
Classes:
public interface IPayload { }
public interface IRequestPayload : IPayload { }
public abstract class Request<T> where T : IRequestPayload {
public T? Payload { get; set; } = null;
}
public class MyAPIRequestPayload : IRequestPayload {
public string Value { get; set; }
}
public class MyAPIRequest : Request<MyAPIRequestPayload> {
}
Desired JSON Input/Output:
{
"Payload":"MyValue"
}
Desired object values:
MyAPIRequest.Payload = instanceof(MyAPIRequestPayload)
MyAPIRequestPayload.Value = "MyValue"
Edit:
Added in the payload marker interfaces.
I am trying to create a bunch of classes/interfaces for use in defining HTTP requests.
The Request class is defined as below
internal class Request : IRequest
{
public Request(Uri uri, Method method, Headers headers)
{
Uri = uri;
Method = method;
Headers = Headers;
}
public IRequestBody Body { get; set; }
}
For IRequestBody I want to be able to define a Type, based on what the request is. For example, a request might contain JSON data, or Form Data.
I tried to define IRequestBody as
public interface IRequestBody<T>
{
RequestBodyType Type { get; }
T Payload { get; }
}
With the hope that I could then define classes such as:
public class FormDataRequestBody : IRequestBody<NameValueCollection>
{
public RequestBodyType Type => RequestBodyType.FormData;
public NameValueCollection Payload => new NameValueCollection();
}
However, on the Request class I must define the Type in the Body property definition. How can I make Body on the Request class generic so I can pass any instance of IRequestBody without knowing the Type upfront?
I have a service that returns the base class response. For sure it has derived responses.
public class ResponseBase
{
public string Response { get; set; }
}
public class DerivedResponse : ResponseBase
{
public string AdditionalResponse { get; set; }
}
Here is the service code:
public class SomeService
{
public ResponseBase GetResponse() => new DerivedResponse();
}
Then I need to handle different responses in different ways. Obviously try to get appropriate behavior via 100500 if\elses is not a good solution. And I decide to have One special response handler for each concrete response.
public interface IHandlerBase<T>
where T : ResponseBase
{
void Handle(T response);
}
public class DerivedResponseHandler : IHandlerBase<DerivedResponse>
{
public void Handle(DerivedResponse response)
{
}
}
Also, we need to encapsulate behavior which will decide what handler to get in order to handle the concrete response and I think not a bad solution for that will be factory. And I got a problem with that because I don't know what to return since I don't know compile-time derived type:
public class HandlerFactory {
public IHandlerBase<> /*WHAT RETURN HERE*/ CreateHandler(ResponseBase response)
{
//decide the derived type of the 'response' and return appropriate handler
}
}
For sure we can remove generic parameter, accept base class in all handlers, then convert to special in the concrete handlers, but I don't think it is a good solution. So could you please advise how to do that in a clean way, maybe some patterns or solutions?
We can do that by creating new NotGeneric interface:
public interface IHandlerBase
{
void Handle(ResponseBase response);
}
public interface IHandlerBase<T> : IHandlerBase
where T : ResponseBase
{
void Handle(T response);
}
public class DerivedResponseHandler : IHandlerBase<DerivedResponse>
{
public void Handle(DerivedResponse response)
{
}
public void Handle(ResponseBase response)
{
var actualParameter = (DerivedResponse) response;
Handle(actualParameter);
}
}
In that case, we have 2 methods in the derived handler: one for actual handling, and another for adapting (something like adapter pattern). The question is it okay, and maybe somebody has a better solution.
For one week I'm getting the below type missmatch error. I search through the internet, looked at how to use generics, but I couldn't find what I'm doing wrong. could anyone please tell me how to fix this problem
static void Main(string[] args) {
JSonHttpClient httpClient;
// ....
public ListAlertsResponse ListAlerts(ListAlertsRequest listAlertsRequest) {
//HERE COUSES THE ERROR !!!
return (ListAlertsResponse)httpClient.DoGetRequest(listAlertsRequest);
}
}
error:
Error 5 Argument 1:
cannot convert from 'ListAlertsRequest' to BaseRequest<BaseResponse>'
My classes and interfaces
public class JsonHttpClient {
public BaseResponse DoGetRequest(BaseRequest<BaseResponse> request) {
return new BaseResponse(...) }
}
public interface Request {}
public interface Response {}
public abstract class BaseResponse : Response {}
public abstract class BaseRequest<T> : Request where T : BaseResponse {}
public class ListAlertsResponse : BaseResponse {}
public class ListAlertsRequest : BaseRequest<ListAlertsResponse> {}
You're sending a type ListAlertsRequest to DoGetRequest which needs a parameter of type BaseRequest<BaseResponse>. ListAlertsRequest is not of type BaseRequest<BaseResponse>
listAlertsRequest is not a subclass of BaseRequest
public class JsonHttpClient
{
public BaseResponse DoGetRequest<T>(BaseRequest<T> request) where T : BaseResponse
{
return new BaseResponse(...)
}
}
DoGetReq returns BaseResponse:
public BaseResponse DoGetRequest(BaseRequest request)
so either return the actual type you're hoping for (ListAlertsResponse), or write a routine to convert it, or (best imo), have ListAlertsResponse take BaseResponse in its constructor and grab whatever info is needed at that point.
A little improvement of T McKeown's answer:
public TResponse DoGetRequest<TResponse>(BaseRequest<TResponse> request)
where TResponse : BaseResponse
{
return default(TResponse);
}
Since BaseRequest is constrained by parameter T, you should put constraint on generic method too. Also, you can omit casting from caller code, using generic return type:
// response is already ListAlertsResponse
var response = httpClient.DoGetRequest(listAlertsRequest);
DoGetRequest returns BaseResponse which you can't cast to a type of a derived class ListAlertsResponse. Think about the following, what if:
public class BaseResponse
{
public int NumberA { get; set; }
}
And the derived class had
public class ListAlertsResponse : BaseResponse
{
public string StringB { get; set; }
}
What do you think this cast will set test.StringB to?
var test = (ListAlertsResponse)httpClient.DoGetRequest(listAlertsRequest);
The runtime doesn't know how to properly cast this for you, if you want to do this, you need to create a converter yourself, or better yet, not do this, you can cast into a base class, but not the other way around.
Basically, I'm trying to do something like this:
SomeRequest request = new SomeRequest();
SomeResponse response = request.GetResponse();
List<Stuff> stuff = response.GetData();
SomeRequest and SomeResponse are classes that both implement the IRequest and IResponse interfaces respectively:
public class SomeRequest : IRequest<SomeResponse>
{
public SomeResponse GetResponse() { ... }
}
public class SomeResponse : IResponse<List<Stuff>>
{
public List<Stuff> GetData() { ... }
}
My IResponse interface looks like this:
public interface IResponse<T>
{
T GetData();
}
The issue I'm running into is with my IRequest interface. I want my IRequest interface's generic (T) to be of type IResponse< T >.
public interface IRequest<T> where T : ?????
{
T GetResponse();
}
I can't figure out what I'm supposed to put after the "where T".
I found two solutions here: C# generic "where constraint" with "any generic type" definition?
The first solution is to specify IResponse< T> generic's type in IRequest like so:
public interface IRequest<T, U> where T : IResponse<U>
but that seems weird because the Request should only have knowledge of the Response and not the type that Response is supposed to return on GetData().
The second option is to create a non-generic interface IResponse and use that in IRequest's generic type constraint, which would look something like this:
public interface IResponse { }
public interface IResponse<T> { ... }
public interface IRequest<T> where T : IResponse
{
BaseResponse GetResponse();
}
This solution however caused a compile error in my SomeRequest class:
public class SomeRequest : IRequest<SomeResponse>
{
public SomeResponse GetResponse() { ... }
}
Error CS0738: SomeRequest does not implement interface member IRequest<SomeResponse>.GetResponse() and the best implementing candidate SomeRequest.GetResponse() return type SomeResponse does not match interface member return type IResponse
So now I'm out of ideas. Any help would be greatly appreciated!
How about:
public interface IRequest<T>
{
IResponse<T> GetResponse();
}
This way you can say things like: new MyRequest().GetResponse().GetData() without having to worry about the exact intermediate response type.
Is it possible you're overcomplicating it? Here's how I implemented what I think you want to do:
public interface IRequest<T>
{
T GetResponse();
}
public interface IResponse<T>
{
T GetData();
}
public class MyRequest : IRequest<MyResponse>
{
public MyResponse GetResponse()
{
return new MyResponse();
}
}
public class MyResponse : IResponse<MyData>
{
public MyData GetData()
{
return new MyData() { Name = "Test" };
}
}
public class MyData
{
public string Name { get; set; }
}
I have my two interfaces, my two implementations of those interfaces, and I can consume them like the following:
MyRequest request = new MyRequest();
MyResponse response = request.GetResponse();
MyData data = response.GetData();