Clean up membership associations on delete.

Closes #85.

app/change_set_persisters/plum_change_set_persister.rb

@@ -60,6 +60,15 @@ def after_save(change_set:, updated_resource:)
 
     def before_delete(change_set:)
       clean_up_collection_associations(change_set: change_set) if change_set.resource.is_a?(Collection)
+      clean_up_membership(change_set: change_set)
+    end
+
+    def clean_up_membership(change_set:)
+      parents = query_service.find_parents(resource: change_set.resource)
+      parents.each do |parent|
+        parent.member_ids -= [change_set.id]
+        persister.save(resource: parent)
+      end
     end
 
     def append(append_id:, updated_resource:)

spec/change_set_persisters/plum_change_set_persister_spec.rb

@@ -151,6 +151,21 @@
     end
   end
 
+  describe "deleting child SRs" do
+    context "when a child is deleted" do
+      it "cleans up associations" do
+        child = FactoryGirl.create_for_repository(:scanned_resource)
+        parent = FactoryGirl.create_for_repository(:scanned_resource, member_ids: child.id)
+        change_set = ScannedResourceChangeSet.new(child)
+
+        change_set_persister.delete(change_set: change_set)
+        reloaded = query_service.find_by(id: parent.id)
+
+        expect(reloaded.member_ids).to eq []
+      end
+    end
+  end
+
   describe "setting visibility" do
     context "when setting to public" do
       it "adds the public read_group" do