Yesod 数据库迁移循环答案

【问题标题】：Yesod database migration loopYesod 数据库迁移循环
【发布时间】：2017-04-12 21:07:37
【问题描述】：

我正在运行 Yesod 并访问 MySQL 数据库。

我的模型是：

User
    ident Text
    password Text Maybe
    UniqueUser ident
    deriving Typeable
Email
    email Text
    userId UserId Maybe
    verkey Text Maybe
    UniqueEmail email
Comment json -- Adding "json" causes ToJSON and FromJSON instances to be derived.
    message Text
    userId UserId Maybe
    deriving Eq
    deriving Show

 -- By default this file is used in Model.hs (which is imported by Foundation.hs)

当我运行 Yesod 应用程序时，它会重复以下内容：

Starting devel application
Migrating: ALTER TABLE `user` ALTER COLUMN `password` DROP DEFAULT
28/Mar/2017:23:46:44 +0200 [Debug#SQL] ALTER TABLE `user` ALTER COLUMN `password` DROP DEFAULT; []
devel.hs: ConnectionError {errFunction = "query", errNumber = 1101, errMessage = "BLOB/TEXT column 'password' can't have a default value"}
Unexpected: child process exited with ExitFailure 1
Trying again
Starting devel application
Migrating: ALTER TABLE `user` ALTER COLUMN `password` DROP DEFAULT
28/Mar/2017:23:46:46 +0200 [Debug#SQL] ALTER TABLE `user` ALTER COLUMN `password` DROP DEFAULT; []
devel.hs: ConnectionError {errFunction = "query", errNumber = 1101, errMessage = "BLOB/TEXT column 'password' can't have a default value"}
Unexpected: child process exited with ExitFailure 1
Trying again

它进入一个永无止境的循环。

解决方法是在Application.hs 中注释以下行，这意味着禁用数据库迁移：

runLoggingT (runSqlPool (runMigration migrateAll) pool) logFunc

但如果我使用解决方法，我会收到另一个错误：

28/Mar/2017:23:56:28 +0200 [Error#yesod-core] Foundation.hs:(137,5)-(144,45): Non-exhaustive patterns in function isAuthorized
 @(yesod-core-1.4.32-6HthMZNCl0sEMRz6GJ4QO1:Yesod.Core.Class.Yesod ./Yesod/Core/Class/Yesod.hs:693:5)
28/Mar/2017:23:56:28 +0200 [Debug#SQL] SELECT `ident`,`password` FROM `user` WHERE `id`=? ; [PersistInt64 1]
GET /test
  Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
  Status: 500 Internal Server Error 0.006514s

【问题讨论】：

标签： haskell database-migration yesod

【解决方案1】：

将default=NULL 添加到每个Text Maybe 列可解决此问题。在某些 MySQL 版本中，您还需要通过添加 sqltype=varchar(255) 来更改列类型。在您的情况下，模型应如下所示：

User
    ident Text
    password Text Maybe sqltype=varchar(255) default=NULL
    UniqueUser ident
    deriving Typeable
Email
    email Text
    userId UserId Maybe
    verkey Text Maybe sqltype=varchar(255) default=NULL
    UniqueEmail email
Comment json -- Adding "json" causes ToJSON and FromJSON instances to be derived.
    message Text
    userId UserId Maybe
    deriving Eq
    deriving Show

 -- By default this file is used in Model.hs (which is imported by Foundation.hs)

【讨论】：

【解决方案2】：

似乎this bug 与迁移和默认值有关。

您可以尝试this workaround 在默认值中更改MySQL 的行为，或者尝试将列的类型从text 更改为varchar？

【讨论】：

谢谢！使用：alter table user modify column password varchar(255) default ' '; 解决了它