Symfony 4 MSSQL sqlsrv:找不到驱动程序

我想将我的项目升级到symfony 4,但条令似乎找不到查找数据库所需的mssql驱动程序。

$ php bin/console doctrine:database:create --env=dev

 In AbstractMySQLDriver.php line 125:

 An exception occurred in driver: could not find driver  

最突出的是,错误发生在MySQLDriver中。php,而我明确告诉symfony我想使用sqlsrv驱动程序。

这是我的信条。yaml设置:

parameters:
    # Adds a fallback DATABASE_URL if the env var is not set.
    # This allows you to run cache:warmup even if your
    # environment variables are not available yet.
    # You should not need to change this value.
    env(DATABASE_URL): 'sqlsrv://my_user:my_password@my_host/my_dbname'

doctrine:
    dbal:
        # configure these for your database server
        driver: 'sqlsrv'
        host: 'my_host'
        user: 'my_user'
        password: 'my_password'
        dbname: 'my_dbname'
        port: 'null'

        #server_version: '5.7'
        #charset: utf8mb4
        default_table_options:
            charset: utf8mb4
            collate: utf8mb4_unicode_ci

        url: '%env(resolve:DATABASE_URL)%'

phpinfo显示可以找到驱动程序

[更新]

webapp显示了一个更清楚的错误。出于某种原因,它正在加载某种默认设置。