push the mysql add_column up to the abstract adapter

activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb

@@ -15,7 +15,7 @@ class IndexDefinition < Struct.new(:table, :name, :unique, :columns, :lengths, :
     # are typically created by methods in TableDefinition, and added to the
     # +columns+ attribute of said TableDefinition object, in order to be used
     # for generating a number of table creation or table changing SQL statements.
-    class ColumnDefinition < Struct.new(:name, :type, :limit, :precision, :scale, :default, :null) #:nodoc:
+    class ColumnDefinition < Struct.new(:name, :type, :limit, :precision, :scale, :default, :null, :first, :after) #:nodoc:
       def string_to_binary(value)
         value
       end
@@ -273,6 +273,8 @@ def new_column_definition(name, type, options) # :nodoc:
         column.scale     = options[:scale]
         column.default   = options[:default]
         column.null      = options[:null]
+        column.first     = options[:first]
+        column.after     = options[:after]
         column
       end
 

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -115,14 +115,13 @@ def accept(o)
 
         def visit_AlterTable(o)
           sql = "ALTER TABLE #{quote_table_name(o.name)} "
+          sql << o.adds.map { |col| visit_AddColumn col }.join(' ')
+        end
 
-          o.adds.each do |col|
-            sql_type = type_to_sql(col.type.to_sym, col.limit, col.precision, col.scale)
-            sql << "ADD #{quote_column_name(col.name)} #{sql_type}"
-            add_column_options!(sql, column_options(col))
-          end
-
-          sql
+        def visit_AddColumn(o)
+          sql_type = type_to_sql(o.type.to_sym, o.limit, o.precision, o.scale)
+          sql = "ADD #{quote_column_name(o.name)} #{sql_type}"
+          add_column_options!(sql, column_options(o))
         end
 
         def visit_ColumnDefinition(o)
@@ -162,6 +161,7 @@ def type_to_sql(type, limit, precision, scale)
 
         def add_column_options!(column_sql, column_options)
           @conn.add_column_options! column_sql, column_options
+          column_sql
         end
       end
 

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -3,6 +3,27 @@
 module ActiveRecord
   module ConnectionAdapters
     class AbstractMysqlAdapter < AbstractAdapter
+      class SchemaCreation < AbstractAdapter::SchemaCreation
+        private
+
+        def visit_AddColumn(o)
+          add_column_position!(super, o)
+        end
+
+        def add_column_position!(sql, column)
+          if column.first
+            sql << " FIRST"
+          elsif column.after
+            sql << " AFTER #{quote_column_name(column.after)}"
+          end
+          sql
+        end
+      end
+
+      def schema_creation
+        SchemaCreation.new self
+      end
+
       class Column < ConnectionAdapters::Column # :nodoc:
         attr_reader :collation, :strict
 
@@ -459,10 +480,6 @@ def rename_table(table_name, new_name)
         rename_table_indexes(table_name, new_name)
       end
 
-      def add_column(table_name, column_name, type, options = {})
-        execute("ALTER TABLE #{quote_table_name(table_name)} #{add_column_sql(table_name, column_name, type, options)}")
-      end
-
       def change_column_default(table_name, column_name, default)
         column = column_for(table_name, column_name)
         change_column table_name, column_name, column.sql_type, :default => default

activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb

@@ -4,16 +4,10 @@ class PostgreSQLAdapter < AbstractAdapter
       class SchemaCreation < AbstractAdapter::SchemaCreation
         private
 
-        def visit_AlterTable(o)
-          sql = "ALTER TABLE #{quote_table_name(o.name)} "
-
-          o.adds.each do |col|
-            sql_type = type_to_sql(col.type.to_sym, col.limit, col.precision, col.scale)
-            sql << "ADD COLUMN #{quote_column_name(col.name)} #{sql_type}"
-            add_column_options!(sql, column_options(col))
-          end
-
-          sql
+        def visit_AddColumn(o)
+          sql_type = type_to_sql(o.type.to_sym, o.limit, o.precision, o.scale)
+          sql = "ADD COLUMN #{quote_column_name(o.name)} #{sql_type}"
+          add_column_options!(sql, column_options(o))
         end
 
         def add_column_options!(sql, options)