c# - 在策略设计模式的情况下，Hangfire 服务器无法选择工作

Question

我有以下申请:

1) Mvc app : Hangfire 客户端，我将从那里排队作业和主机 仪表板。此应用程序将包含我的类库的引用。

2) Console App : Hangfire 服务器将存在于这个控制台应用程序中。

3) 类库:hangfire 服务器(控制台应用程序)和 hangfire 客户端(asp.net mvc)之间的共享库，我的长期运行代码将驻留在其中。Hangfire 服务器 将执行该库的代码。

我在类库中的结构如下 strategy design pattern.

代码取自:Reference:

接口(interface):

public interface IOperation
{
    Output Process(Input input);
    bool AppliesTo(Type type);
}

public interface IOperationStrategy
{
    Output Process(Type type,Input input);
}

操作:

public class Add : IOperation
{
    public bool AppliesTo(Type type)
        {
            return typeof(Add).Equals(type);
        }

    public Output Process(Input input)
    {
        // Implementation
        return new Output();
    }
}

public class Multiply : IOperation
{
     public bool AppliesTo(Type type)
        {
            return typeof(Multiply).Equals(type);
        }

    public Output Process(Input input)
    {
        // Implementation
        return new Output();
    }
}

策略:

public class OperationStrategy : IOperationStrategy
{
    private readonly IOperation[] operations;

    public OperationStrategy(params IOperation[] operations)
    {
        if (operations == null)
            throw new ArgumentNullException(nameof(operations));
        this.operations = operations;
    }

    public Output Process(Type type, Input input)
    {
        var op = operations.FirstOrDefault(o => o.AppliesTo(type));
        if (op == null)
            throw new InvalidOperationException($"{operation} not registered.");

        return op.Process(input);
    }
}

用法:

// Do this with your DI container in your composition 
// root, and the instance would be created by injecting 
// it somewhere.
var strategy = new OperationStrategy(
    new Add(), // Inject any dependencies for operation here
    new Multiply()); // Inject any dependencies for operation here

// And then once it is injected, you would simply do this.
var input = new Input { Value1 = 2, Value2 = 3 };
BackgroundJob.Enqueue(() => strategy.Process(typeof(Add), input));

但是 hangfire 服务器无法选择作业，当我检查 state table 时，我看到如下错误:

"FailedAt": "2018-03-21T13:14:46.0172303Z", "ExceptionType": "System.MissingMethodException", "ExceptionMessage": "No parameterless constructor defined for this object.", "ExceptionDetails": "System.MissingMethodException: No parameterless constructor defined for this object.\r\n at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)\r\n at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)\r\n at System.Activator.CreateInstance(Type type, Boolean nonPublic)\r\n at System.Activator.CreateInstance(Type type)\r\n at Hangfire.JobActivator.SimpleJobActivatorScope.Resolve(Type type)\r\n at Hangfire.Server.CoreBackgroundJobPerformer.Perform(PerformContext context)\r\n at Hangfire.Server.BackgroundJobPerformer.<>c__DisplayClass8_0.b__0()\r\n at Hangfire.Server.BackgroundJobPerformer.InvokePerformFilter(IServerFilter filter, PerformingContext preContext, Func 1 continuation)\r\n at Hangfire.Server.BackgroundJobPerformer.PerformJobWithFilters(PerformContext context, IEnumerable`1 filters)\r\n at Hangfire.Server.BackgroundJobPerformer.Perform(PerformContext context)\r\n at Hangfire.Server.Worker.PerformJob(BackgroundProcessContext context, IStorageConnection connection, String jobId)"

我不知道应该为这个结构设置什么 hangfire，因为我这里没有涉及任何 IOC 容器。

有人可以帮我解决这个问题吗？

演示项目:https://www.dropbox.com/s/bfjr58y6azgmm3w/HFDemo.zip?dl=0

Answer 1

答案就在异常中

没有为此对象定义无参数构造函数。

您的 OperationStrategy 没有无参数构造函数，因此当 Hangfire 尝试创建此对象时，它不能 - 它通过反射来创建。Hangfire 无法访问您在安排作业时使用的实例，它会尝试重新创建它。这是它做不到的。

您可以添加一个无参数的构造函数，并使 Operations 成为一个公共(public)集合。

这将使您能够像当前一样使用您的 ctor，但也允许对象被序列化，由 Hangfire 存储，然后在它尝试运行时反序列化和创建。

public class OperationStrategy : IOperationStrategy
{
    // paramaterless ctor
    public OperationStrategy()
    {
        Operations = new List<Operation>(); 
    }

    public OperationStrategy(params IOperation[] operations)
    {
        if (operations == null)
            throw new ArgumentNullException(nameof(operations));

        Operations = operations;
    }

    public Output Process(Type type, Input input)
    {
        var op = Operations.FirstOrDefault(o => o.AppliesTo(type));

        if (op == null)
            throw new InvalidOperationException($"{operation} not registered.");

        return op.Process(input);
    }

    //property - this can be deserialized by Hangfire
    public List<IOperation> Operations {get; set;}
}