Comments for your migrations

Tested on:

ActiveRecord 5.0

Using Ruby 2.2 and higher

ActiveRecord 4.2

using Ruby 2.1 and higher

Status: Build Status


ActiveRecord 5.0 is introducing baked-in comment support, although not all features provided by this project have yet been completely implemented. This is expected to be rectified by ActiveRecord 5.1, and as such ActiveRecord 5.0 will likely be the last version for which this gem will work (or be needed). ActiveRecord 5.0 itself will be supported by this project, but many features are overlapping and you may find that you won't need it at all.

For those using a version of ActiveRecord prior to 4.2 or of Ruby prior to 2.1, please use the v0.3.2 version of the gem.


Migrations are wonderful. They handle all your schema changes, and in a pinch they can bring any database up to speed. However, database schemas can change rapidly while a project is maturing, and it can be difficult to know (or remember) the purpose for each table and field. As such, they deserve to be commented. These comments should be available for display wherever those fields are found.


Using MigrationComments, you can simply add comments during your migrations. Or if you already have existing data structures, just add the comments afterwards in a separate migration. And of course you can always modify and delete these comments in later migrations.

So where are these comments used? Firstly, they will be included in your schema.rb dump which is where your IDE (e.g. RubyMine, TextMate) should be learning about your model structure. This means that they'll be available at any point in your project. Additionally, if you are using the 'annotate’ gem, these comments will be added to the annotations that are generated within your model.rb file.


To add a comment to an existing structure…

def self.up
  set_table_comment :table_name, "A table comment"
  set_column_comment :table_name, :column_name, "A column comment"

Or you can use the change_table macro…

def self.up
  change_table :table_name do |t|
    t.comment "A table comment"
    t.change_comment :column_name, "A column comment"

Creating a new table?

def self.up
  create_table :table_name, :comment => "A table comment" do |t|
    t.string :column_name, :comment => "A column comment"

You can also remove comments…

def self.up
  remove_table_comment :table_name
  remove_column_comment :table_name, :column_name

Or you can combine these commands while modifying a table…

def self.up
  change_table :existing_table do |t|
    t.comment nil                                       # remove an existing table comment
    t.string :new_column, :comment => "a new column"    # add a new column with a comment
    t.change_comment :existing_column, nil              # remove a comment on an existing column
    t.integer :another_existing_column, :comment => nil # remove a comment on an existing column while modifying the column type
    t.boolean :column_with_comment                      # modify an existing column without altering the comment


You must be using a supported DBMS (currently PostgreSQL, MySQL, and SQLite).

If this isn't an option for you, check out the 'schema_comments' gem at github.com/akm/schema_comments


See MIT-LICENSE file for details.