[wip] add a unique constraint

db/migrate/20190110224307_unique_constraint.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class UniqueConstraint < ActiveRecord::Migration[5.2]
+  def change
+    add_index :workflow_steps,
+              %i[druid version datastream process],
+              unique: true,
+              name: 'uk_workflow_steps'
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_01_10_221945) do
+ActiveRecord::Schema.define(version: 2019_01_10_224307) do
 
   create_table "workflow_steps", force: :cascade do |t|
     t.string "druid", null: false
@@ -29,6 +29,7 @@
     t.string "lane_id", default: "default", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["druid", "version", "datastream", "process"], name: "uk_workflow_steps", unique: true
     t.index ["druid", "version"], name: "index_workflow_steps_on_druid_and_version"
     t.index ["druid"], name: "index_workflow_steps_on_druid"
   end

spec/controllers/workflows_controller_spec.rb

@@ -67,16 +67,41 @@
     let(:workflow) { 'accessionWF' }
     let(:repository) { 'dor' }
     let(:request_data) { workflow_create }
-    let(:client) { double(current_version: '1') }
+    let(:client) { double(current_version: current_version) }
+    let(:expected_count) { Nokogiri::XML(workflow_create).xpath('//process').count }
 
     before do
       allow(Dor::Services::Client).to receive(:object).with(druid).and_return(client)
     end
-    it 'creates new workflows' do
-      expect do
-        put :create, body: request_data, params: { repo: repository, druid: druid, workflow: workflow, format: :xml }
-      end.to change(WorkflowStep, :count)
-        .by(Nokogiri::XML(workflow_create).xpath('//process').count)
+
+    context 'when no workflows exist' do
+      let(:current_version) { '1' }
+
+      it 'creates new workflows' do
+        expect do
+          put :create, body: request_data, params: { repo: repository, druid: druid, workflow: workflow, format: :xml }
+        end.to change(WorkflowStep, :count)
+          .by(expected_count)
+      end
+    end
+
+    context 'when some workflows exist' do
+      let(:current_version) { '2' }
+      before do
+        WorkflowParser.new(
+          workflow_create,
+          druid: druid,
+          repository: repository,
+          version: '1'
+        ).create_workflow_steps
+      end
+
+      it 'creates new workflows' do
+        expect do
+          put :create, body: request_data, params: { repo: repository, druid: druid, workflow: workflow, format: :xml }
+        end.to change(WorkflowStep, :count)
+          .by(expected_count)
+      end
     end
   end
 end