Add support for specifying comments for tables, columns, and indexes.

Comments are specified in migrations, stored in database itself (in its schema),
and dumped into db/schema.rb file.

This allows to generate good documentation and explain columns and tables' purpose
to everyone from new developers to database administrators.

For PostgreSQL and MySQL only. SQLite does not support comments at the moment.

See docs for PostgreSQL: http://www.postgresql.org/docs/current/static/sql-comment.html
See docs for MySQL: http://dev.mysql.com/doc/refman/5.7/en/create-table.html

1 files changed, 18 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb
index 1e2c859af9..5ab81640e8 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb
@@ -2,6 +2,9 @@ module ActiveRecord
   module ConnectionAdapters
     module MySQL
       class SchemaCreation < AbstractAdapter::SchemaCreation
+        delegate :quote, to: :@conn
+        private :quote
+
         private
 
         def visit_DropForeignKey(name)
@@ -22,6 +25,13 @@ module ActiveRecord
           add_column_position!(change_column_sql, column_options(o.column))
         end
 
+        def add_table_options!(sql, options)
+          super
+          if options[:comment]
+            sql << "COMMENT #{quote(options[:comment])} "
+          end
+        end
+
         def column_options(o)
           column_options = super
           column_options[:charset] = o.charset
@@ -35,7 +45,11 @@ module ActiveRecord
           if options[:collation]
             sql << " COLLATE #{options[:collation]}"
           end
-          super
+          new_sql = super
+          if options[:comment]
+            new_sql << " COMMENT #{quote(options[:comment])}"
+          end
+          new_sql
         end
 
         def add_column_position!(sql, options)
@@ -48,8 +62,9 @@ module ActiveRecord
         end
 
         def index_in_create(table_name, column_name, options)
-          index_name, index_type, index_columns, _, _, index_using = @conn.add_index_options(table_name, column_name, options)
-          "#{index_type} INDEX #{quote_column_name(index_name)} #{index_using} (#{index_columns}) "
+          index_name, index_type, index_columns, _, _, index_using, comment = @conn.add_index_options(table_name, column_name, options)
+          index_option = " COMMENT #{quote(comment)}" if comment
+          "#{index_type} INDEX #{quote_column_name(index_name)} #{index_using} (#{index_columns})#{index_option} "
         end
       end
     end