Question

I’d like to insert COMMENT, which is part of SQL the command, in my migration files.

As far as I know, I can add COMMENT to each table and column.

I can’t remember a plugin name that lets me to write as follows:

    t.string  :name, :comment => "A user's fullname"
    t.string  :label, :comment => "name of color"
    t.text  :value, :comment => "self intro"
    t.integer  :position, :comment => "1 is left, 2 is right"

And that statement magically is translated into SQL, which is like

create table test (
  name varchar(255) not null COMMENT 'blahblah',
  label varchar(255) null COMMENT 'hahaha'
  text varchar(255) not null,
  position int(11)
);

Does anybody know the plug in name?

---

• I’m not looking for Annotate Models plugins by Dave Thomas. What I mean by comments is inside MySQL queries.

Answer 1

I don’t know of any plugin that will accomplish what you’re asking for. You might be able to hack in what you want by looking at ActiveRecord::ConnectionAdapters::ColumnDefinition. (See active_record/connection_adapters/abstract/schema_definitions.rb.)

As you can see the Struct defines the various column options (like :limit and :default.) You could extended that struct with a :comment and then modify #to_sql to generate the required SQL. You would also need to modify TableDefinition#column to set the :comment attribute.

The following has been tested and works (for MySQL):

module ActiveRecord
  module ConnectionAdapters
    class ColumnDefinition
      attr_accessor :comment

      def to_sql_with_comment
        column_sql = to_sql_without_comment
        return column_sql if comment.nil?
       "#{column_sql} COMMENT '#{base.quote_string(comment)}'"
      end

      alias_method_chain :to_sql, :comment
    end

    class TableDefinition
      # Completely replaces (and duplicates the existing code, but there's
      # no place to really hook into the middle of this.)
      def column(name, type, options = {})
        column = self[name] || ColumnDefinition.new(@base, name, type)
        if options[:limit]
          column.limit = options[:limit]
        elsif native[type.to_sym].is_a?(Hash)
          column.limit = native[type.to_sym][:limit]
        end
        column.precision = options[:precision]
        column.scale = options[:scale]
        column.default = options[:default]
        column.null = options[:null]
        column.comment = options[:comment]
        @columns << column unless @columns.include? column
        self
      end
    end
  end
end