Yii2 设计模式——工厂方法模式

//获取数据表元数据
public function getTableSchema($name, $refresh = false)
{
    if (array_key_exists($name, $this->_tables) && !$refresh) {
        return $this->_tables[$name];
    }

    $db = $this->db;
    $realName = $this->getRawTableName($name);

    if ($db->enableSchemaCache && !in_array($name, $db->schemaCacheExclude, true)) {
        /* @var $cache Cache */
        $cache = is_string($db->schemaCache) ? Yii::$app->get($db->schemaCache, false) : $db->schemaCache;
        if ($cache instanceof Cache) {
            $key = $this->getCacheKey($name);
            if ($refresh || ($table = $cache->get($key)) === false) {
                //通过工厂方法loadTableSchema()去获取TableSchema实例
                $this->_tables[$name] = $table = $this->loadTableSchema($realName);
                if ($table !== null) {
                    $cache->set($key, $table, $db->schemaCacheDuration, new TagDependency([
                        ‘tags‘ => $this->getCacheTag(),
                    ]));
                }
            } else {
                $this->_tables[$name] = $table;
            }

            return $this->_tables[$name];
        }
    }
    //通过工厂方法loadTableSchema()去获取TableSchema实例
    return $this->_tables[$name] = $this->loadTableSchema($realName);
}

//获取TableSchema实例，让子类去实现
abstract protected function loadTableSchema($name);