Migrate epic_issues position values correctly

db/migrate/20171214115254_add_position_to_epic_issues.rb

@@ -6,7 +6,7 @@ class AddPositionToEpicIssues < ActiveRecord::Migration
   disable_ddl_transaction!
 
   def up
-    add_column_with_default(:epic_issues, :position, :integer, default: Arel.sql('id'), allow_null: false)
+    add_column_with_default(:epic_issues, :position, :integer, default: 1, allow_null: false)
   end
 
   def down

db/migrate/20171221154744_set_epic_issue_position_values.rb

+class SetEpicIssuePositionValues < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  class Epic < ActiveRecord::Base
+    self.table_name = 'epics'
+  end
+
+  class EpicIssue < ActiveRecord::Base
+    self.table_name = 'epic_issues'
+  end
+
+  def up
+    epic_issues = select_all('SELECT id, epic_id FROM epic_issues ORDER by epic_id, id')
+      .group_by { |e| e['epic_id'] }
+
+    epic_issues.each do |epic_id, epic_issues|
+      epic_issues.each_with_index do |epic_issue, index|
+        execute("UPDATE epic_issues SET position = #{index + 1} WHERE id = #{epic_issue['id']}")
+      end
+    end
+  end
+
+  def down
+    execute('UPDATE epic_issues SET position = 1')
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20171214115254) do
+ActiveRecord::Schema.define(version: 20171221154744) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -765,7 +765,7 @@ ActiveRecord::Schema.define(version: 20171214115254) do
   create_table "epic_issues", force: :cascade do |t|
     t.integer "epic_id", null: false
     t.integer "issue_id", null: false
-    t.integer "position", default: 0, null: false
+    t.integer "position", default: 1, null: false
   end
 
   add_index "epic_issues", ["epic_id"], name: "index_epic_issues_on_epic_id", using: :btree

spec/migrations/set_epic_issue_position_values.rb

+require 'spec_helper'
+require Rails.root.join('db', 'migrate', '20171221154744_set_epic_issue_position_values.rb')
+
+describe SetEpicIssuePositionValues, :migration do
+  let(:groups) { table(:namespaces) }
+  let(:projects) { table(:projects) }
+  let(:users) { table(:users) }
+  let(:issues) { table(:issues) }
+  let(:epics) { table(:epics) }
+  let(:epic_issues) { table(:epic_issues) }
+
+  let(:group) { groups.create(name: 'group', path: 'group') }
+  let(:project) { projects.create(name: 'group', namespace_id: group.id) }
+  let(:user) { users.create(username: 'User') }
+
+  let(:epic1) { epics.create(title: 'Epic 1', title_html: 'Epic 1', group_id: group.id, author_id: user.id, iid: 1) }
+  let(:epic2) { epics.create(title: 'Epic 1', title_html: 'Epic 1', group_id: group.id, author_id: user.id, iid: 1) }
+
+  let(:issue1) { issues.create(title: 'Issue 1', title_html: 'Issue 1', project_id: project.id, author_id: user.id) }
+  let(:issue2) { issues.create(title: 'Issue 2', title_html: 'Issue 1', project_id: project.id, author_id: user.id) }
+  let(:issue3) { issues.create(title: 'Issue 3', title_html: 'Issue 1', project_id: project.id, author_id: user.id) }
+  let(:issue4) { issues.create(title: 'Issue 4', title_html: 'Issue 1', project_id: project.id, author_id: user.id) }
+  let(:issue5) { issues.create(title: 'Issue 5', title_html: 'Issue 1', project_id: project.id, author_id: user.id) }
+
+  let!(:epic_issue1) { epic_issues.create!(epic_id: epic1.id, issue_id: issue1.id) }
+  let!(:epic_issue2) { epic_issues.create!(epic_id: epic1.id, issue_id: issue2.id) }
+  let!(:epic_issue3) { epic_issues.create!(epic_id: epic2.id, issue_id: issue3.id) }
+  let!(:epic_issue4) { epic_issues.create!(epic_id: epic2.id, issue_id: issue4.id) }
+  let!(:epic_issue5) { epic_issues.create!(epic_id: epic2.id, issue_id: issue5.id) }
+
+  it 'sets the position value correctly' do
+    migrate!
+
+    expect(epic_issue1.reload.position).to eq(1)
+    expect(epic_issue2.reload.position).to eq(2)
+    expect(epic_issue3.reload.position).to eq(1)
+    expect(epic_issue4.reload.position).to eq(2)
+    expect(epic_issue5.reload.position).to eq(3)
+  end
+end