Add existence checks before creating the timelogs table and time_estimate columns

Signed-off-by: Rémy Coutable <remy@rymai.me>

db/migrate/20161030005533_add_estimate_to_issuables.rb

-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
 class AddEstimateToIssuables < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
 
-  # Set this constant to true if this migration requires downtime.
   DOWNTIME = false
 
-  # When a migration requires downtime you **must** uncomment the following
-  # constant and define a short and easy to understand explanation as to why the
-  # migration requires downtime.
-  # DOWNTIME_REASON = ''
-
-  # When using the methods "add_concurrent_index" or "add_column_with_default"
-  # you must disable the use of transactions as these methods can not run in an
-  # existing transaction. When using "add_concurrent_index" make sure that this
-  # method is the _only_ method called in the migration, any other changes
-  # should go in a separate migration. This ensures that upon failure _only_ the
-  # index creation fails and can be retried or reverted easily.
-  #
-  # To disable transactions uncomment the following line and remove these
-  # comments:
-  # disable_ddl_transaction!
-
   def up
-    add_column :issues, :time_estimate, :integer
-    add_column :merge_requests, :time_estimate, :integer
+    unless column_exists?(:issues, :time_estimate)
+      add_column :issues, :time_estimate, :integer
+    end
+
+    unless column_exists?(:merge_requests, :time_estimate)
+      add_column :merge_requests, :time_estimate, :integer
+    end
   end
 
   def down
-    remove_column :issues, :time_estimate
-    remove_column :merge_requests, :time_estimate
+    if column_exists?(:issues, :time_estimate)
+      remove_column :issues, :time_estimate
+    end
+
+    if column_exists?(:merge_requests, :time_estimate)
+      remove_column :merge_requests, :time_estimate
+    end
   end
 end

db/migrate/20161030020610_create_timelogs.rb

@@ -3,16 +3,22 @@ class CreateTimelogs < ActiveRecord::Migration
 
   DOWNTIME = false
 
-  def change
-    create_table :timelogs do |t|
-      t.integer :time_spent, null: false
-      t.references :trackable, polymorphic: true
-      t.references :user
+  def up
+    unless table_exists?(:timelogs)
+      create_table :timelogs do |t|
+        t.integer :time_spent, null: false
+        t.references :trackable, polymorphic: true
+        t.references :user
 
-      t.timestamps null: false
+        t.timestamps null: false
+      end
+
+      add_index :timelogs, [:trackable_type, :trackable_id]
+      add_index :timelogs, :user_id
     end
+  end
 
-    add_index :timelogs, [:trackable_type, :trackable_id]
-    add_index :timelogs, :user_id
+  def down
+    drop_table :timelogs if table_exists?(:timelogs)
   end
 end