Api controller declaring more than one Get statement

This is all in the routing. The default Web API route looks like this:

config.Routes.MapHttpRoute( 
    name: "API Default", 
    routeTemplate: "api/{controller}/{id}", 
    defaults: new { id = RouteParameter.Optional } 
);

With the default routing template, Web API uses the HTTP method to select the action. In result it will map a GET request with no parameters to first GetAll it can find. To work around this you need to define a route where the action name is included:

config.Routes.MapHttpRoute( 
   name: "ActionApi", 
   routeTemplate: "api/{controller}/{action}/{id}", 
   defaults: new { id = RouteParameter.Optional } 
);

After that you can star making requests with following URL’s:

• api/yourapicontroller/GetClients
• api/yourapicontroller/GetStaffMembers

This way you can have multiple GetAll in Controller.

One more important thing here is that with this style of routing, you must use attributes to specify the allowed HTTP methods (like [HttpGet]).

There is also an option of mixing the default Web API verb based routing with traditional approach, it is very well described here:

• Web API: Mixing Traditional & Verb-Based Routing