在 Laravel 6 的数据库迁移中，修改字段的类型

1、现在表 theme_asset 的字段 theme_id，其类型为 varchar(255)。之前的迁移代码如下 。如图1

$table->string('theme_id')->nullable(false)->comment('主题Id');

2、现在计划新增加一个迁移文件，以修改字段 theme_id 的类型为：uuid，即 char(36)。

$table->uuid('theme_id')->change();

3、报错：Doctrine\DBAL\Exception : Unknown column type “uuid” requested. 如图2

PS E:\wwwroot\object> php artisan module:migrate ThemeStoreDB
Migrating: 2022_05_20_160818_update_theme_asset_table

   Doctrine\DBAL\Exception  : Unknown column type "uuid" requested. Any Doctrine type that you use has to be registered with \Doctrine\DBAL\Types\Type::addType(). You can get a list of all the known types with \Doctrine\DBAL\Types\Type::getTypesMap(). If this error occurs during database introspection then you might have forgotten to register all database types for a Doctrine Type. Use AbstractPlatform#registerDoctrineTypeMapping() or have your custom types implement Type#getMappedDatabaseTypes(). If the type name is empty you might have a problem with the cache or forgot some mapping information.

  at E:\wwwroot\object\vendor\doctrine\dbal\lib\Doctrine\DBAL\DBALException.php:282
    278|      * @return Exception
    279|      */    280|     public static function unknownColumnType($name)
    281|     {
  > 282|         return new Exception('Unknown column type "' . $name . '" requested. Any Doctrine type that you use has ' .
    283|             'to be registered with \Doctrine\DBAL\Types\Type::addType(). You can get a list of all the ' .
    284|             'known types with \Doctrine\DBAL\Types\Type::getTypesMap(). If this error occurs during database ' .
    285|             'introspection then you might have forgotten to register all database types for a Doctrine Type. Use ' .
    286|             'AbstractPlatform#registerDoctrineTypeMapping() or have your custom types implement ' .

  Exception trace:

  1   Doctrine\DBAL\DBALException::unknownColumnType("uuid")
      E:\wwwroot\object\vendor\doctrine\dbal\lib\Doctrine\DBAL\Types\TypeRegistry.php:37

  2   Doctrine\DBAL\Types\TypeRegistry::get("uuid")
      E:\wwwroot\object\vendor\doctrine\dbal\lib\Doctrine\DBAL\Types\Type.php:237

  Please use the argument -v to see more details.

4、调整为 char 后，仍然报错：Unknown column type “char” requested.

$table->char('theme_id', 36)->change();

5、最终决定使用 DB::statement，代码如下

DB::statement('ALTER TABLE ' . DB::connection()->getTablePrefix() . 'theme_asset MODIFY theme_id char(36) NOT NULL COMMENT \'文件内容\'');

6、查看 生成表的 SQL 对比，符合预期。如图3

`theme_id` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL COMMENT '主题Id',

`theme_id` char(36) COLLATE utf8mb4_unicode_ci NOT NULL COMMENT '主题Id',