错误：ALTER TYPE ... ADD 不能在事务块内运行

Question

我正在尝试向 PostgreSQL 中的现有类型添加新类型值。但我收到以下错误

错误：ALTER TYPE ... ADD 无法在事务块内运行

我用来为类型添加新值的查询是

ALTER TYPE public.request_type ADD VALUE "Check";

我实际上是在使用 node-pg-migrate 创建的迁移文件中运行上面的查询

public 是我的架构。

知道为什么会失败吗？

编辑：

以下查询在pgadmin中执行时执行良好

ALTER TYPE public.request_type ADD VALUE "Check";

但是当我通过 node-pg-migrate 迁移运行上述命令时，它会失败并抛出上述错误

Answer 1

具体如何使用node-pg-migrate 执行此操作是禁用迁移事务：

exports.up = (pgm) => {
  pgm.noTransaction()
  pgm.addTypeValue('foo', 'BAR', { ifNotExists: true })
}

Answer 2

如上所述，您不能在事务块内编辑枚举。但是您可以创建新的。步骤如下：

1. 将所有使用此类型的列/表的类型从 request_type 更改为 varchar：

ALTER TABLE table_name
    ALTER COLUMN column_name TYPE VARCHAR(255);

1. 删除并再次创建 request_type 枚举：

DROP TYPE IF EXISTS request_type;
CREATE TYPE request_type AS ENUM (
    'OLD_VALUE_1',
    'OLD_VALUE_2',
    'NEW_VALUE_1',
    'NEW_VALUE_2'
);

1. 将所有列/表的类型从 varchar 恢复为 request_type（恢复第一步）：

ALTER TABLE table_name
    ALTER COLUMN column_name TYPE request_type
    USING (column_name::request_type);

Answer 3

您可以将查询更改为

COMMIT;
ALTER TYPE public.request_type ADD VALUE "Check";

Answer 4

PostgreSQL 早期版本的解决方法shown here：

请注意，这需要特殊权限，因为它会更改系统表。

• 将'NEW_ENUM_VALUE' 替换为您想要的值。
• 将'type_egais_units' 替换为您要更改的枚举的oid。 （使用SELECT * FROM pg_enum 查找要更新的枚举，在我的例子中是一个5 位数字，例如'19969'）

声明：

INSERT INTO pg_enum (
    enumtypid, 
    enumlabel, 
    enumsortorder
)
SELECT 
    'type_egais_units'::regtype::oid, 
    'NEW_ENUM_VALUE', 
    (SELECT MAX(enumsortorder) + 1 FROM pg_enum WHERE enumtypid = 'type_egais_units'::regtype)

当然，按照公认答案中的建议升级 PostgreSQL 可能是最好的。

有谁知道从 pgAdmin 版本 3.5 运行查询时如何避免使用事务？ （即使用 F5 执行时？）

Answer 5

原因在AlterEnumsrc/backend/commands/typecmds.c中的以下评论中给出：

/*
 * Ordinarily we disallow adding values within transaction blocks,
 * because we can't cope with enum OID values getting into indexes and
 * then having their defining pg_enum entries go away.  However, it's
 * okay if the enum type was created in the current transaction, since
 * then there can be no such indexes that wouldn't themselves go away
 * on rollback.  (We support this case because pg_dump
 * --binary-upgrade needs it.)

请注意，此限制已在 commit 212fab99 中删除；提交信息如下：

To prevent possibly breaking indexes on enum columns, we must keep
uncommitted enum values from getting stored in tables, unless we
can be sure that any such column is new in the current transaction.

Formerly, we enforced this by disallowing ALTER TYPE ... ADD VALUE
from being executed at all in a transaction block, unless the target
enum type had been created in the current transaction.  This patch
removes that restriction, and instead insists that an uncommitted enum
value can't be referenced unless it belongs to an enum type created
in the same transaction as the value.  Per discussion, this should be
a bit less onerous.  It does require each function that could possibly
return a new enum value to SQL operations to check this restriction,
but there aren't so many of those that this seems unmaintainable.

所以您可能想尽快升级到 PostgreSQL v12 :^)