我创建了一个带有自定义实例存储的简单工作流服务（以支持 oracle）。自定义实例存储，我遵循 MSDN 的演示：[http://msdn.microsoft.com/en-us/library/ee829481.aspx][1] 但是当我调用服务 api 时，引发异常：
从实例存储中检索到错误类型的值。需要一个类型为 {/Default Web Site/}OrderService.svc 的值，但是却遇到了 null。
我尝试使用SqlWorkflowInstanceStore，没问题。服务没有问题。我再次使用自定义实例存储并调试，我发现LoadWorkflowCommand在SaveWorkflowCommand之前执行。我认为这是一个问题。需要你的帮助！
以下是我的代码片段：
1. Web Config:
<extensions>
<behaviorExtensions>
<add name="databaseWorkflowInstanceStore" type="Practices.Framework.Workflow.Configuration.DatabaseInstanceStoreElement, Practices.Framework" />
</behaviorExtensions>
</extensions>
<behaviors>
<serviceBehaviors>
<behavior>
<!--<sqlWorkflowInstanceStore connectionStringName="practicesDatabase" instanceCompletionAction="DeleteAll" instanceEncodingOption="GZip" />-->
<databaseWorkflowInstanceStore database="practicesDatabase" />
<serviceDebug includeExceptionDetailInFaults="true" />
</behavior>
</serviceBehaviors>
</behaviors>
2. DatabaseInstanceStore
public class DatabaseInstanceStore : InstanceStore
{
protected override IAsyncResult BeginTryCommand(InstancePersistenceContext context, InstancePersistenceCommand command, TimeSpan timeout, AsyncCallback callback, object state)
{
if (command is CreateWorkflowOwnerCommand)
{
var instanceOwnerId = Guid.NewGuid();
context.BindInstanceOwner(instanceOwnerId, instanceOwnerId);
}
else if (command is LoadWorkflowCommand)
{
var instanceData = this.LoadInstanceData();
context.LoadedInstance(InstanceState.Initialized, instanceData, null, null, null);
}
else if (command is SaveWorkflowCommand)
{
var saveCommand = (SaveWorkflowCommand)command;
var instanceData = saveCommand.InstanceData;
this.SaveInstanceData(instanceData);
}
return new CompletedAsyncResult<bool>(true, callback, state);
}
......
}