fix deploy problems due to renamed table

db/fixtures/999_delayed.rb

@@ -0,0 +1,12 @@
+# Delayed migration steps
+
+require 'table_migration_helper'
+
+TableMigrationHelper.delayed_drop(
+  old_name: 'topic_status_updates',
+  new_name: 'topic_timers',
+  after_migration: 'RenameTopicStatusUpdatesToTopicTimers',
+  on_drop: ->(){
+    STDERR.puts "Dropping topic_status_updates. It was moved to topic_timers."
+  }
+)

db/migrate/20170512185227_create_topic_status_updates_again.rb

@@ -0,0 +1,23 @@
+require 'table_migration_helper'
+
+class CreateTopicStatusUpdatesAgain < ActiveRecord::Migration
+  def up
+    create_table :topic_status_updates do |t|
+      t.datetime :execute_at, null: false
+      t.integer :status_type, null: false
+      t.integer :user_id, null: false
+      t.integer :topic_id, null: false
+      t.boolean :based_on_last_post, null: false, default: false
+      t.datetime :deleted_at
+      t.integer :deleted_by_id
+      t.timestamps
+      t.integer :category_id
+    end
+
+    TableMigrationHelper.read_only_table('topic_status_updates')
+  end
+
+  def down
+    drop_table :topic_status_updates
+  end
+end

lib/table_migration_helper.rb

@@ -0,0 +1,53 @@
+class TableMigrationHelper
+  def self.read_only_table(table_name)
+    ActiveRecord::Base.exec_sql <<-SQL
+    CREATE OR REPLACE FUNCTION raise_read_only() RETURNS trigger AS $rro$
+      BEGIN
+        RAISE EXCEPTION 'Table is read only';
+        RETURN null;
+      END
+    $rro$ LANGUAGE plpgsql;
+    SQL
+
+    ActiveRecord::Base.exec_sql <<-SQL
+    CREATE TRIGGER #{table_name}_read_only
+    BEFORE INSERT OR UPDATE OR DELETE OR TRUNCATE
+    ON #{table_name}
+    FOR EACH STATEMENT
+    EXECUTE PROCEDURE raise_read_only();
+    SQL
+  end
+
+  def self.delayed_drop(old_name:, new_name:, after_migration:, delay: nil, on_drop: nil)
+    delay ||= Rails.env.production? ? 300 : 0
+
+   sql = <<SQL
+    SELECT 1
+    FROM INFORMATION_SCHEMA.TABLES
+    WHERE table_schema = 'public' AND
+          table_name = :old_name AND
+          EXISTS (
+            SELECT 1
+            FROM schema_migration_details
+            WHERE name = :after_migration AND
+                  created_at <= (current_timestamp at time zone 'UTC' - interval :delay)
+          )
+          AND EXISTS (
+            SELECT 1
+            FROM INFORMATION_SCHEMA.TABLES
+            WHERE table_schema = 'public' AND
+            table_name = :new_name
+          )
+    LIMIT 1
+SQL
+
+    if ActiveRecord::Base.exec_sql(sql, old_name: old_name,
+                                        new_name: new_name,
+                                        delay: "#{delay.to_i || 0} seconds",
+                                        after_migration: after_migration).to_a.length > 0
+        on_drop&.call
+
+        ActiveRecord::Base.exec_sql("DROP TABLE #{old_name}")
+    end
+  end
+end

spec/components/table_migration_helper_spec.rb

@@ -0,0 +1,66 @@
+require 'rails_helper'
+require 'table_migration_helper'
+
+describe TableMigrationHelper do
+
+  def table_exists?(table_name)
+    sql = <<-SQL
+    SELECT 1
+    FROM INFORMATION_SCHEMA.TABLES
+    WHERE table_schema = 'public' AND
+          table_name = '#{table_name}'
+    SQL
+
+    ActiveRecord::Base.exec_sql(sql).to_a.length > 0
+  end
+
+  describe '#delayed_drop' do
+    it "can drop a table after correct delay and when new table exists" do
+      ActiveRecord::Base.exec_sql "CREATE TABLE table_with_old_name (topic_id INTEGER)"
+
+      name = ActiveRecord::Base
+              .exec_sql("SELECT name FROM schema_migration_details LIMIT 1")
+              .getvalue(0,0)
+
+      Topic.exec_sql("UPDATE schema_migration_details SET created_at = :created_at WHERE name = :name",
+                    name: name, created_at: 15.minutes.ago)
+
+      dropped_proc_called = false
+
+      described_class.delayed_drop(
+        old_name: 'table_with_old_name',
+        new_name: 'table_with_new_name',
+        after_migration: name,
+        delay: 20.minutes,
+        on_drop: ->(){dropped_proc_called = true}
+      )
+
+      expect(table_exists?('table_with_old_name')).to eq(true)
+      expect(dropped_proc_called).to eq(false)
+
+      described_class.delayed_drop(
+        old_name: 'table_with_old_name',
+        new_name: 'table_with_new_name',
+        after_migration: name,
+        delay: 10.minutes,
+        on_drop: ->(){dropped_proc_called = true}
+      )
+
+      expect(table_exists?('table_with_old_name')).to eq(true)
+      expect(dropped_proc_called).to eq(false)
+
+      ActiveRecord::Base.exec_sql "CREATE TABLE table_with_new_name (topic_id INTEGER)"
+
+      described_class.delayed_drop(
+        old_name: 'table_with_old_name',
+        new_name: 'table_with_new_name',
+        after_migration: name,
+        delay: 10.minutes,
+        on_drop: ->(){dropped_proc_called = true}
+      )
+
+      expect(table_exists?('table_with_old_name')).to eq(false)
+      expect(dropped_proc_called).to eq(true)
+    end
+  end
+end