Allow only one binding for v2 API

Author: johha

app/actions/v2/services/service_binding_create.rb

@@ -29,6 +29,7 @@ def create(app, service_instance, message, volume_mount_services_enabled, accept
       raise SpaceMismatch unless bindable_in_space?(service_instance, app.space)
 
       raise_if_instance_locked(service_instance)
+      raise_if_binding_already_exists(service_instance, app)
 
       binding = ServiceBinding.new(
         service_instance: service_instance,
@@ -82,6 +83,12 @@ def bindable_in_space?(service_instance, app_space)
       service_instance.space == app_space || service_instance.shared_spaces.include?(app_space)
     end
 
+    def raise_if_binding_already_exists(service_instance, app)
+      return unless ServiceBinding.where(service_instance:, app:).any?
+
+      raise CloudController::Errors::ApiError.new_from_details('ServiceBindingAppServiceTaken', 'The app is already bound to the service.')
+    end
+
     def logger
       @logger ||= Steno.logger('cc.action.service_binding_create')
     end