Service Stack migrating RPC to REST issues - servicestack

Question

Trying to sell a move to ServiceStack from traditional ASP.Net /SOAP web services with the management team.
I am struggling with a some RPC'ish issues. Requirement is that I support SOAP (even backhandedly) in the hope of selling my service consumers on REST.
Take for example a service called "ReplaceItem" which basically requires:
Close out item number
Replacement item number
Store Number
Bunch of other replacement item data
Should I create a ReplacementItem DTO? It seems to be if I have a number of these type of functions I am just going to have tons of DTOs instead of tons of RPC methods. Plus what is the "id" in this case and what REST method would I be using?
I get that REST/SS gives me basic CRUD functionality for domain level structures like Items/Customers/etc, but how do I handle non-CRUD methods in SS.
I am also having issues with multiple parameters making up the primary key for a certain service. Almost all Inventory tables are structured by Item Number AND Store Number. I'd rather not dump the creation of some composite string on the service client. How do I handle this?
Thanks.

Answer 1

ServiceStack promotes a SOA-like message-based design that is optimal and provides many natural benefits for remote services.
My initial thoughts would look something like
POST {CloseItemNumber} /item/1/close
POST {ItemNumber} /item/1?replace=true
POST {ItemNumber} /item/1
POST {ItemNumber} /item/1 i.e. same DTO/service different values.
Where ItemNumber and CloseItemNumber are separate Request DTOs and services.
Designing Service APIs
I prefer to structure my services around 'resources/nouns' and design my service APIs as actions that apply operations to them.
If the operation requires more information than storing the Resource DTO I would create a separate service with the additional metadata.
i.e. Here's how I would convert Amazons 'RPC' service to be more REST-ful:
https://ec2.amazonaws.com/?Action=AttachVolume
&VolumeId=vol-4d826724
&InstanceId=i-6058a509
&Device=/dev/sdh
&AUTHPARAMS
Into how I prefer to write it:
POST https://ec2.amazonaws.com/volumes/vol-4d826724/attach
FormData: InstanceId=i-6058a509&Device=/dev/sdh&AUTHPARAMS
Which would still use an explicit AttachVolume Request DTO.
Another example I use to showcase the different between WCF RPC and ServiceStack's coarse-grained message-based approach is in: https://gist.github.com/1386381
Difference between an RPC-chatty and message-based API:
This is a typical API that WCF encourages:
public interface IService
{
Customer GetCustomerById(int id);
Customer[] GetCustomerByIds(int[] id);
Customer GetCustomerByUserName(string userName);
Customer[] GetCustomerByUserNames(string[] userNames);
Customer GetCustomerByEmail(string email);
Customer[] GetCustomerByEmails(string[] emails);
}
This is an equivalent message-based API we encourage in ServiceStack:
public class Customers {
int[] Ids;
string[] UserNames;
string[] Emails;
}
public class CustomersResponse {
Customer[] Results;
}
Note: If you want your same services to support a both SOAP and a REST-based API, you will need to structure your services slightly differently to overcome SOAP's limitation of tunnelling all operations through HTTP POST.

Answer 2

Problem i still have when deciding to switch from 1 chatty RPC api to a REST api is that instead of having several functions easy to maintain, i find myself with either 2 solutions :
multiplying DTOs and services that makes internal code for the services being chatty and complex
or
putting into a single route (OnGet) all the code managing the service but this way i have to parse the different parameters to 'discover' which parameters have been requested (to simplify instead of having multiple simple functions with pre-defined parameters i now have only one function that has to determine which parameters are meaningful ... but that is VERY hard to maintain - code is more complex to me now).
In the proposed solution to solve GetCustomerById, GetCustomersByEmails etc. the point to me is that instead of having simple queries, we now have to dynamically construct the query based on the filled parameters - that can make the code tricky and hard to maintain - having to manage possible combinations of multiple parameters - some combinations not being possible too.
Feeling little bit sad about that as i REALLY don't like WCF at all.
Mixing WCF and REST seems summum of the complexity - the worst for me (complexity of defining a REST api + complexity of WCF).
Are my feelings shared or did i miss something ?