Doctrine\ORM\Tools\SchemaTool::_gatherColumn PHP Method

    private function _gatherColumn($class, array $mapping, $table)
    {
        $columnName = $class->getQuotedColumnName($mapping['fieldName'], $this->_platform);
        $columnType = $mapping['type'];

        $options = array();
        $options['length'] = isset($mapping['length']) ? $mapping['length'] : null;
        $options['notnull'] = isset($mapping['nullable']) ? ! $mapping['nullable'] : true;
        if ($class->isInheritanceTypeSingleTable() && count($class->parentClasses) > 0) {
            $options['notnull'] = false;
        }

        $options['platformOptions'] = array();
        $options['platformOptions']['version'] = $class->isVersioned && $class->versionField == $mapping['fieldName'] ? true : false;

        if(strtolower($columnType) == 'string' && $options['length'] === null) {
            $options['length'] = 255;
        }

        if (isset($mapping['precision'])) {
            $options['precision'] = $mapping['precision'];
        }

        if (isset($mapping['scale'])) {
            $options['scale'] = $mapping['scale'];
        }

        if (isset($mapping['default'])) {
            $options['default'] = $mapping['default'];
        }

        if (isset($mapping['columnDefinition'])) {
            $options['columnDefinition'] = $mapping['columnDefinition'];
        }

        if ($class->isIdGeneratorIdentity() && $class->getIdentifierFieldNames() == array($mapping['fieldName'])) {
            $options['autoincrement'] = true;
        }

        if ($table->hasColumn($columnName)) {
            // required in some inheritance scenarios
            $table->changeColumn($columnName, $options);
        } else {
            $table->addColumn($columnName, $columnType, $options);
        }

        $isUnique = isset($mapping['unique']) ? $mapping['unique'] : false;
        if ($isUnique) {
            $table->addUniqueIndex(array($columnName));
        }
    }