Quartz.Net数据库作业仅单例添加可用，动态添加触发空引用异常求助

我开发了一个将作业存入数据库并按需调度的程序。此前在Program.cs中以单例方式添加作业可正常运行，但每个调度器仅能添加一个作业，且无法检查作业是否已存在。因此我将作业添加逻辑移至调度器中，先检查数据库中是否存在目标作业，不存在则添加。

作业可成功添加，但完全无法运行，调用时会触发来自JobRunShell.Run()的NullReferenceException。作业在数据库中的状态看起来完全正常，代码也未发现错误。这种添加作业的方式是否不正确？

以单例添加作业的Program.cs代码 #

builder.Services.AddSingleton<IJobFactory, JobFactory>();
builder.Services.AddSingleton<ISchedulerFactory, StdSchedulerFactory>();
builder.Services.AddSingleton<MailHRNewEmployee>();
builder.Services.AddSingleton(new JobMetadata(Guid.NewGuid(), typeof(MailHRNewEmployee), "HR First Contact", "job blueprint"));
builder.Services.AddHostedService<MyScheduler>();

MyScheduler.cs代码 #

public async Task StartAsync(CancellationToken cancellationToken)
{
    //Creating Scheduler
    Scheduler = await schedulerFactory.GetScheduler();
    Scheduler.JobFactory = jobFactory;

    //Start Scheduler
    await Scheduler.Start(cancellationToken);

    //Create Jobs
    var istrue = await Scheduler.CheckExists(new JobKey("HR First Contact", "DEFAULT"));
    if (!(bool)istrue)
    {
        jobMetaData = new JobMetadata(Guid.NewGuid(), typeof(MailHRNewEmployee), "HR First Contact", "job blueprint");
        IJobDetail jobDetail = CreateJob(jobMetaData);
        await Scheduler.AddJob(jobDetail, true);
    }

...(checking all the other jobs)

private IJobDetail CreateJob(JobMetadata jobMetadata)
{
    return JobBuilder.Create(jobMetaData.JobType).WithIdentity(jobMetaData.JobName.ToString()).StoreDurably(true).WithDescription(jobMetaData.JobDescription).Build();
}

NullReferenceException异常栈 #

[10:43:31 ERR] Job DEFAULT.HR First Contact threw an unhandled Exception: 
System.NullReferenceException: Object reference not set to an instance of an object.
   at Quartz.Core.JobRunShell.Run(CancellationToken cancellationToken)
[10:43:32 ERR] Job DEFAULT.HR First Contact threw an exception.
Quartz.SchedulerException: Job threw an unhandled exception.
 ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Quartz.Core.JobRunShell.Run(CancellationToken cancellationToken)
   --- End of inner exception stack trace --- [See nested exception: System.NullReferenceException: Object reference not set to an instance of an object.
   at Quartz.Core.JobRunShell.Run(CancellationToken cancellationToken)]

补充说明：
我尝试使用MS DI集成库配合Quartz托管服务，但无法使其与持久化作业存储及MySQL配合工作。

builder.Services.Configure<QuartzOptions>(builder.Configuration.GetSection("Quartz"));
builder.Services.Configure<QuartzOptions>(options =>
{
    options.Scheduling.IgnoreDuplicates = true;
    options.Scheduling.OverWriteExistingData = true;
});

builder.Services.AddQuartz(q =>
{
    q.SchedulerId = "Job Creator";
    q.UseMicrosoftDependencyInjectionJobFactory();


    var jobKey = new JobKey("HR First Contact", "DEFAULT");
    q.AddJob<MailHRNewEmployee>(jobKey, j => j
        .StoreDurably()
        .WithDescription("job blueprint"));

    q.UsePersistentStore(s =>
    {
        s.PerformSchemaValidation = true;
        s.UseProperties = true;
        s.RetryInterval = TimeSpan.FromSeconds(15);
        //Neither .UseMySql nor UseMySqlConnector work
        //MySqlConnector should be the one I want though
        s.UseMySqlConnector(MySql =>
        {
            //I am loading the configuration above but don't know how to use the connection string here?
            //I thought it would maybe be Configuration.GetConnectionString("xyz");
            MySql.ConnectionString = "MyConnectionString";
            MySql.TablePrefix = "QRTZ_";
        });
        s.UseJsonSerializer();
    });
});
builder.Services.AddTransient<MailHRNewEmployee>();

builder.Services.AddQuartzHostedService(options =>
{
    options.WaitForJobsToComplete = true;
});

一、调度器内添加作业导致空引用的修复 #

1. 修正CreateJob方法的参数错误 #

你的CreateJob方法参数是jobMetadata，但方法内误用了类成员jobMetaData（大小写不一致），如果类成员未初始化，会导致JobDetail关联错误的类型信息，直接引发空引用。修复代码：

private IJobDetail CreateJob(JobMetadata jobMetadata)
{
    return JobBuilder.Create(jobMetadata.JobType)
        .WithIdentity(jobMetadata.JobName)
        .StoreDurably(true)
        .WithDescription(jobMetadata.JobDescription)
        .Build();
}

2. 确保作业实例能被DI容器正确解析 #

动态添加作业时，必须保证作业类型（如MailHRNewEmployee）已注册到DI容器，且自定义JobFactory能正确从容器获取实例：

• 注册作业：使用AddTransient或AddScoped（单例仅适用于无状态作业）：

  builder.Services.AddTransient<MailHRNewEmployee>();
  

• 检查自定义JobFactory实现，确保正确解析实例：

  public class JobFactory : IJobFactory
  {
      private readonly IServiceProvider _serviceProvider;
  
      public JobFactory(IServiceProvider serviceProvider)
      {
          _serviceProvider = serviceProvider;
      }
  
      public IJob NewJob(TriggerFiredBundle bundle, IScheduler scheduler)
      {
          return _serviceProvider.GetRequiredService(bundle.JobDetail.JobType) as IJob;
      }
  
      public void ReturnJob(IJob job)
      {
          if (job is IDisposable disposable)
          {
              disposable.Dispose();
          }
      }
  }
  

二、MS DI集成库配合MySQL持久化的配置修复 #

1. 安装正确的NuGet包 #

确保已安装：

• Quartz.Extensions.DependencyInjection
• Quartz.Persistence.MySqlConnector（使用官方MySqlConnector驱动，而非旧版MySql.Data）

2. 正确读取连接字符串 #

通过配置文件读取连接字符串，避免硬编码：

q.UsePersistentStore(s =>
{
    s.PerformSchemaValidation = true;
    s.UseProperties = true;
    s.RetryInterval = TimeSpan.FromSeconds(15);
    s.UseMySqlConnector(MySql =>
    {
        MySql.ConnectionString = builder.Configuration.GetConnectionString("QuartzMySQL");
        MySql.TablePrefix = "QRTZ_";
        MySql.MySqlVersion = new Version(8, 0, 28); // 指定MySQL版本避免兼容性问题
    });
    s.UseJsonSerializer();
});

在appsettings.json中添加连接字符串配置：

"ConnectionStrings": {
    "QuartzMySQL": "server=localhost;database=quartz;user=root;password=你的密码;SslMode=None;"
}

3. 动态添加作业的适配 #

如果需要动态检查并添加作业，不要在AddQuartz中硬编码作业注册，而是通过IScheduler在托管服务中动态处理，避免重复注册冲突。

内容的提问来源于stack exchange，提问作者Jat