Make some params optional for add-on purchase update endpoint

The update endpoint for a subscription add-on purchase required the
`quantity`, `expires_on` and `purchase_xid` params. For the
deprovisioning of a subscription add-on purchase, only the
`expires_on` will be synced. The other two params are therefore made
optional for the update endpoint.

doc/development/internal_api/index.md

@@ -857,9 +857,9 @@ PUT /namespaces/:id/subscription_add_on_purchase/:add_on_name
 
 | Attribute   | Type    | Required | Description |
 |:------------|:--------|:---------|:------------|
-| `quantity` | integer | yes | Amount of units in the subscription add-on purchase (Example: Number of seats for a code suggestions add-on) |
+| `quantity` | integer | no | Amount of units in the subscription add-on purchase (Example: Number of seats for a code suggestions add-on) |
 | `expires_on` | date | yes | Expiration date of the subscription add-on purchase |
-| `purchase_xid` | string | yes | Identifier for the subscription add-on purchase (Example: Subscription name for a code suggestions add-on) |
+| `purchase_xid` | string | no | Identifier for the subscription add-on purchase (Example: Subscription name for a code suggestions add-on) |
 
 Example request:
 

ee/app/services/gitlab_subscriptions/add_on_purchases/update_service.rb

@@ -23,11 +23,13 @@ def add_on_purchase
       # rubocop: enable CodeReuse/ActiveRecord
 
       def update_add_on_purchase
-        add_on_purchase.update(
+        attributes = {
           quantity: quantity,
           expires_on: expires_on,
           purchase_xid: purchase_xid
-        )
+        }.compact
+
+        add_on_purchase.update(attributes)
       end
 
       def error_response

ee/lib/api/gitlab_subscriptions/add_on_purchases.rb

@@ -16,14 +16,6 @@ class AddOnPurchases < ::API::Base
       end
 
       resource :namespaces, requirements: ::API::API::NAMESPACE_OR_PROJECT_REQUIREMENTS do
-        helpers do
-          params :purchased_subscription_add_on_attributes do
-            requires :quantity, type: Integer, desc: 'The quantity of the purchase'
-            requires :expires_on, type: Date, desc: 'The date when purchase expires on'
-            requires :purchase_xid, type: String, desc: 'The purchase identifier (example: the subscription name)'
-          end
-        end
-
         desc 'Create an add-on purchase for the namespace' do
           detail 'Creates a subscription add-on record for the given namespaces and add-on'
           success ::EE::API::Entities::GitlabSubscriptions::AddOnPurchase
@@ -34,7 +26,9 @@ class AddOnPurchases < ::API::Base
           ]
         end
         params do
-          use :purchased_subscription_add_on_attributes
+          requires :quantity, type: Integer, desc: 'The quantity of the purchase'
+          requires :expires_on, type: Date, desc: 'The date when purchase expires on'
+          requires :purchase_xid, type: String, desc: 'The purchase identifier (example: the subscription name)'
         end
         post ":id/subscription_add_on_purchase/:add_on_name" do
           result = ::GitlabSubscriptions::AddOnPurchases::CreateService.new(
@@ -78,7 +72,9 @@ class AddOnPurchases < ::API::Base
           ]
         end
         params do
-          use :purchased_subscription_add_on_attributes
+          requires :expires_on, type: Date, desc: 'The date when purchase expires on'
+          optional :quantity, type: Integer, desc: 'The quantity of the purchase'
+          optional :purchase_xid, type: String, desc: 'The purchase identifier (example: the subscription name)'
         end
         put ":id/subscription_add_on_purchase/:add_on_name" do
           result = ::GitlabSubscriptions::AddOnPurchases::UpdateService.new(

ee/spec/requests/api/gitlab_subscriptions/add_on_purchases_spec.rb

@@ -234,7 +234,7 @@
 
         context 'when the add-on purchase exists' do
           let_it_be(:expires_on) { Date.current + 6.months }
-          let_it_be(:add_on_purchase) do
+          let_it_be_with_reload(:add_on_purchase) do
             create(
               :gitlab_subscription_add_on_purchase,
               namespace: namespace,
@@ -245,7 +245,7 @@
             )
           end
 
-          it 'creates a new add-on purchase' do
+          it 'updates the found add-on purchase' do
             expect do
               put_add_on_purchase
               add_on_purchase.reload
@@ -263,6 +263,28 @@
             )
           end
 
+          context 'with only required params' do
+            let(:params) { { expires_on: (Date.current + 1.year).to_s } }
+
+            it 'updates the add-on purchase' do
+              expect do
+                put_add_on_purchase
+                add_on_purchase.reload
+              end.to change { add_on_purchase.expires_on }.from(expires_on).to(params[:expires_on].to_date)
+                .and not_change { add_on_purchase.quantity }
+
+              expect(response).to have_gitlab_http_status(:success)
+              expect(json_response).to eq(
+                'namespace_id' => namespace_id,
+                'namespace_name' => namespace.name,
+                'add_on' => add_on.name.titleize,
+                'quantity' => add_on_purchase.quantity,
+                'expires_on' => params[:expires_on],
+                'purchase_xid' => add_on_purchase.purchase_xid
+              )
+            end
+          end
+
           context 'when the add-on purchase cannot be saved' do
             let(:params) { super().merge(quantity: 0) }