Using change_column will leave default if the type does not change or a new default is not included. Fixes issue #22.

Author: metaskills

CHANGELOG

@@ -1,6 +1,9 @@
 
 MASTER
 
+* Using change_column will leave default if the type does not change or a new default
+  is not included. Fixes issue #22. [Ransom Briggs]
+
 * Use correct SP name for sp_MSforeachtable so any collation can get to it. [7to3]
 
 * Qualify INFORMATION_SCHEMA.COLUMNS with a correct period DB name if present.

lib/active_record/connection_adapters/sqlserver_adapter.rb

@@ -653,10 +653,13 @@ def remove_column(table_name, *column_names)
 
       def change_column(table_name, column_name, type, options = {})
         sql_commands = []
-        remove_default_constraint(table_name, column_name)
+        column_object = columns(table_name).detect { |c| c.name.to_s == column_name.to_s }
         change_column_sql = "ALTER TABLE #{quote_table_name(table_name)} ALTER COLUMN #{quote_column_name(column_name)} #{type_to_sql(type, options[:limit], options[:precision], options[:scale])}"
         change_column_sql << " NOT NULL" if options[:null] == false
         sql_commands << change_column_sql
+        if options_include_default?(options) || (column_object && column_object.type != type.to_sym)
+         	remove_default_constraint(table_name,column_name)
+        end
         if options_include_default?(options)
           remove_sqlserver_columns_cache_for(table_name)
           sql_commands << "ALTER TABLE #{quote_table_name(table_name)} ADD CONSTRAINT #{default_name(table_name,column_name)} DEFAULT #{quote(options[:default])} FOR #{quote_column_name(column_name)}"

test/cases/migration_test_sqlserver.rb

@@ -46,9 +46,21 @@ def setup
       assert lock_version_column.default.nil?
     end
 
+    should 'not drop the default contraint if just renaming' do
+      find_default = lambda do 
+        @connection.select_all("EXEC sp_helpconstraint 'defaults','nomsg'").select do |row|     
+          row['constraint_type'] == "DEFAULT on column decimal_number"
+        end.last
+      end
+      default_before = find_default.call
+      @connection.change_column :defaults, :decimal_number, :decimal, :precision => 4
+      default_after = find_default.call
+      assert default_after
+      assert_equal default_before['constraint_keys'], default_after['constraint_keys']
+    end
+    
   end
 
-  
 end