Hangfire大家都很熟了，在.net 下用处很多，最近在asp.net core 3.1 使用hangfire的过程中,遇到很多问题，现在记录下来，分享给下一位。
1.现在的开发环境：
asp.net core 3.1
hangfire.aspnetcore 1.7.9
mysql 8.0.12
hangfire.mysql.core 2.2.5
2.遇到的第一个异常解决：
{"code":401,"data":"","message":"Parameter '@rownum' must be defined. To use this as a variable, set 'Allow User Variables=true' in the connection string."}
这个我查了一些资料，解决办法是在连接字符串添加AllowUserVariables=True;得以解决
你的连接字符串看起来应该像这样：
Server=myServerAddress;Database=myDataBase;Uid=myUsername;Pwd=myPassword;
AllowUserVariables=True;
网上搜索到的，有提示变量为Allow User Variables=true（注意中间有空格），经我实践是不行的，需要使用AllowUserVariables=True;（中间没有空格） 这样的方式。
3.遇到下面的类似的异常：
{"code":401,"data":"","message":"You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'rank\r\n\t from `Hangfire_Set`,\r\n (select @rownum := 0) r \r\n w' at line 3"}
经查，原来我们是引用：Hangfire.MySqlStorage
这个库来实现mysql版本下的hangfire数据持久化。这个库现在已经不实用了。
建议换成：
Hangfire.MySql.Core
这个库
4.换成以上库以后，使用方式如下：
services.AddHangfire(x => x.UseStorage(new MySqlStorage(Configuration.GetConnectionString("Hangfire"),new MySqlStorageOptions(){TablePrefix = "Custom"})));
支持表前缀为custom,不需要添加下划线，表会自动创建custom_的表。
5.以下异常：
MySqlException: Table ' custom__distributedlock' doesn't exist
要注意，表脚本要跟着修改一下：
从原来12张表新增了一张表，变为13张表，
增加了表：DistributedLock
github上有脚本，为了方便大家，我把脚本贴一下，直接用这个修改就可以了：
-- ----------------------------
-- Table structure for `Job`
-- ----------------------------
CREATE TABLE `_Job` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`StateId` int(11) DEFAULT NULL,
`StateName` varchar(20) DEFAULT NULL,
`InvocationData` longtext NOT NULL,
`Arguments` longtext NOT NULL,
`CreatedAt` datetime NOT NULL,
`ExpireAt` datetime DEFAULT NULL,
PRIMARY KEY (`Id`),
KEY `IX_Job_StateName` (`StateName`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Table structure for `Counter`
-- ----------------------------
CREATE TABLE `_Counter` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`Key` varchar(100) NOT NULL,
`Value` int(11) NOT NULL,
`ExpireAt` datetime DEFAULT NULL,
PRIMARY KEY (`Id`),
KEY `IX_Counter_Key` (`Key`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
CREATE TABLE `_AggregatedCounter` (
Id int(11) NOT NULL AUTO_INCREMENT,
`Key` varchar(100) NOT NULL,
`Value` int(11) NOT NULL,
ExpireAt datetime DEFAULT NULL,
PRIMARY KEY (`Id`),
UNIQUE KEY `IX_CounterAggregated_Key` (`Key`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Table structure for `DistributedLock`
-- ----------------------------
CREATE TABLE `_DistributedLock` (
`Resource` varchar(100) NOT NULL,
`CreatedAt` datetime NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Table structure for `Hash`
-- ----------------------------
CREATE TABLE `_Hash` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`Key` varchar(100) NOT NULL,
`Field` varchar(40) NOT NULL,
`Value` longtext,
`ExpireAt` datetime DEFAULT NULL,
PRIMARY KEY (`Id`),
UNIQUE KEY `IX_Hash_Key_Field` (`Key`,`Field`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Table structure for `JobParameter`
-- ----------------------------
CREATE TABLE `_JobParameter` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`JobId` int(11) NOT NULL,
`Name` varchar(40) NOT NULL,
`Value` longtext,
PRIMARY KEY (`Id`),
CONSTRAINT `IX_JobParameter_JobId_Name` UNIQUE (`JobId`,`Name`),
KEY `FK_JobParameter_Job` (`JobId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Table structure for `JobQueue`
-- ----------------------------
CREATE TABLE `_JobQueue` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`JobId` int(11) NOT NULL,
`Queue` varchar(50) NOT NULL,
`FetchedAt` datetime DEFAULT NULL,
`FetchToken` varchar(36) DEFAULT NULL,
PRIMARY KEY (`Id`),
INDEX `IX_JobQueue_QueueAndFetchedAt` (`Queue`,`FetchedAt`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Table structure for `JobState`
-- ----------------------------
CREATE TABLE `_JobState` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`JobId` int(11) NOT NULL,
`Name` varchar(20) NOT NULL,
`Reason` varchar(100) DEFAULT NULL,
`CreatedAt` datetime NOT NULL,
`Data` longtext,
PRIMARY KEY (`Id`),
KEY `FK_JobState_Job` (`JobId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Table structure for `Server`
-- ----------------------------
CREATE TABLE `_Server` (
`Id` varchar(100) NOT NULL,
`Data` longtext NOT NULL,
`LastHeartbeat` datetime DEFAULT NULL,
PRIMARY KEY (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Table structure for `Set`
-- ----------------------------
CREATE TABLE `_Set` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`Key` varchar(100) NOT NULL,
`Value` varchar(256) NOT NULL,
`Score` float NOT NULL,
`ExpireAt` datetime DEFAULT NULL,
PRIMARY KEY (`Id`),
UNIQUE KEY `IX_Set_Key_Value` (`Key`,`Value`)
) ENGINE=InnoDB CHARSET=utf8mb4;
CREATE TABLE `_State`
(
Id int(11) NOT NULL AUTO_INCREMENT,
JobId int(11) NOT NULL,
Name varchar(20) NOT NULL,
Reason varchar(100) NULL,
CreatedAt datetime NOT NULL,
Data longtext NULL,
PRIMARY KEY (`Id`),
KEY `FK_HangFire_State_Job` (`JobId`)
) ENGINE=InnoDB CHARSET=utf8mb4;
CREATE TABLE `_List`
(
`Id` int(11) NOT NULL AUTO_INCREMENT,
`Key` varchar(100) NOT NULL,
`Value` longtext NULL,
`ExpireAt` datetime NULL,
PRIMARY KEY (`Id`)
) ENGINE=InnoDB CHARSET=utf8mb4;