1 files changed, 29 insertions, 14 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 1797af4e97..cea5a04006 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -77,10 +77,14 @@ module ActiveRecord
         }
       end
 
-      def version
+      def version #:nodoc:
         @version ||= Version.new(full_version.match(/^\d+\.\d+\.\d+/)[0])
       end
 
+      def mariadb? # :nodoc:
+        full_version =~ /mariadb/i
+      end
+
       # Returns true, since this connection adapter supports migrations.
       def supports_migrations?
         true
@@ -156,8 +160,8 @@ module ActiveRecord
         raise NotImplementedError
       end
 
-      def new_column(field, default, sql_type_metadata, null, table_name, default_function = nil, collation = nil) # :nodoc:
-        MySQL::Column.new(field, default, sql_type_metadata, null, table_name, default_function, collation)
+      def new_column(field, default, sql_type_metadata, null, table_name, default_function = nil, collation = nil, comment = nil) # :nodoc:
+        MySQL::Column.new(field, default, sql_type_metadata, null, table_name, default_function, collation, comment)
       end
 
       # Must return the MySQL error number from the exception, if the exception has an
@@ -369,7 +373,7 @@ module ActiveRecord
               mysql_index_type = row[:Index_type].downcase.to_sym
               index_type  = INDEX_TYPES.include?(mysql_index_type)  ? mysql_index_type : nil
               index_using = INDEX_USINGS.include?(mysql_index_type) ? mysql_index_type : nil
-              indexes << IndexDefinition.new(row[:Table], row[:Key_name], row[:Non_unique].to_i == 0, [], [], nil, nil, index_type, index_using)
+              indexes << IndexDefinition.new(row[:Table], row[:Key_name], row[:Non_unique].to_i == 0, [], [], nil, nil, index_type, index_using, row[:Index_comment].presence)
             end
 
             indexes.last.columns << row[:Column_name]
@@ -390,10 +394,18 @@ module ActiveRecord
           else
             default, default_function = field[:Default], nil
           end
-          new_column(field[:Field], default, type_metadata, field[:Null] == "YES", table_name, default_function, field[:Collation])
+          new_column(field[:Field], default, type_metadata, field[:Null] == "YES", table_name, default_function, field[:Collation], field[:Comment].presence)
         end
       end
 
+      def table_comment(table_name)
+        select_value(<<-SQL.strip_heredoc, 'SCHEMA')
+          SELECT table_comment
+          FROM INFORMATION_SCHEMA.TABLES
+          WHERE table_name=#{quote(table_name)};
+        SQL
+      end
+
       def create_table(table_name, options = {}) #:nodoc:
         super(table_name, options.reverse_merge(:options => "ENGINE=InnoDB"))
       end
@@ -478,8 +490,10 @@ module ActiveRecord
       end
 
       def add_index(table_name, column_name, options = {}) #:nodoc:
-        index_name, index_type, index_columns, _, index_algorithm, index_using = add_index_options(table_name, column_name, options)
-        execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}"
+        index_name, index_type, index_columns, _, index_algorithm, index_using, comment = add_index_options(table_name, column_name, options)
+        sql = "CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}"
+        sql << " COMMENT #{quote(comment)}" if comment
+        execute sql
       end
 
       def foreign_keys(table_name)
@@ -517,7 +531,12 @@ module ActiveRecord
         raw_table_options = create_table_info.sub(/\A.*\n\) /m, '').sub(/\n\/\*!.*\*\/\n\z/m, '').strip
 
         # strip AUTO_INCREMENT
-        raw_table_options.sub(/(ENGINE=\w+)(?: AUTO_INCREMENT=\d+)/, '\1')
+        raw_table_options.sub!(/(ENGINE=\w+)(?: AUTO_INCREMENT=\d+)/, '\1')
+
+        # strip COMMENT
+        raw_table_options.sub!(/ COMMENT='.+'/, '')
+
+        raw_table_options
       end
 
       # Maps logical Rails types to MySQL-specific data types.
@@ -782,10 +801,6 @@ module ActiveRecord
         subselect.from subsubselect.as('__active_record_temp')
       end
 
-      def mariadb?
-        full_version =~ /mariadb/i
-      end
-
       def supports_rename_index?
         mariadb? ? false : version >= '5.7.6'
       end
@@ -866,8 +881,8 @@ module ActiveRecord
         create_table_info_cache[table_name] ||= select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
       end
 
-      def create_table_definition(name, temporary = false, options = nil, as = nil) # :nodoc:
-        MySQL::TableDefinition.new(name, temporary, options, as)
+      def create_table_definition(name, temporary = false, options = nil, as = nil, comment = nil) # :nodoc:
+        MySQL::TableDefinition.new(name, temporary, options, as, comment)
       end
 
       def integer_to_sql(limit) # :nodoc: