Ensure uniqueness of workflows by instance Id

[rosca-sabina]

Hello,

Is there a way to ensure that only one workflow with a given InstanceId is ever created?

Currently if I call workflowRuntime.StartWorkflowAsync(definitionId, new StartWorkflowRuntimeParams { InstanceId = myUniqueInstanceId }), allow it to finish running the workflow, and then make the same call with the same arguments, it starts running the workflow again from the beginning, even though a finished workflow with InstanceId myUniqueInstanceId already exists.

Is there a way to prevent the DefaultWorkflowRuntime from starting a new workflow if a wokflow with the same InstanceId already exists?

[glime-ai[bot]]

To ensure that only one workflow with a given InstanceId is ever created, you can use the IWorkflowInstanceStore to check if a workflow instance with the specified InstanceId already exists before attempting to start a new workflow. You can create a specification that checks for the existence of a workflow instance with the given InstanceId and use the CountAsync method to determine if an instance already exists.

Here's an example of how you might implement this check:

var instanceId = "myUniqueInstanceId"; // The unique instance ID you want to check for
var workflowDefinitionId = "yourWorkflowDefinitionId"; // The definition ID of the workflow

// Get the IWorkflowInstanceStore service
var workflowInstanceStore = serviceProvider.GetRequiredService<IWorkflowInstanceStore>();

// Setup query specification
var specification = new WorkflowInstanceSpecification().WithWorkflowDefinitionId(workflowDefinitionId).WithWorkflowInstanceId(instanceId);

// Count matching results
var existingInstanceCount = await workflowInstanceStore.CountAsync(specification);

if (existingInstanceCount == 0)
{
    // No existing workflow instance found, safe to start a new one
    var workflowRuntime = serviceProvider.GetRequiredService<IWorkflowRuntime>();
    await workflowRuntime.StartWorkflowAsync(definitionId, new StartWorkflowRuntimeOptions { InstanceId = myUniqueInstanceId });
}
else
{
    // A workflow with the specified InstanceId already exists
    // Handle this case as needed (e.g., return an error, do nothing, etc.)
}

Please note that the WorkflowInstanceSpecification class used in the example is a hypothetical class that you would need to implement based on your application's requirements and the Elsa Workflow version you are using. The actual class name and methods may differ.

If you are using Elsa 2.x or later, you can also consider using the IWorkflowLaunchpad service, which is responsible for executing workflows in response to triggers. It provides methods to start or resume workflows, and you can extend its behavior to include the uniqueness check as described above.

Remember to handle concurrency issues that may arise if multiple requests try to start a workflow with the same InstanceId simultaneously.

This comment was generated by Glime.

[rosca-sabina]

Can I use an IActivationStrategy in my workflow definition to achieve this?

[rosca-sabina]

You can implement interface IWorkflowActivationStrategy, and then use your custom implementation in your workflow by calling builder.WithActivationStrategyType<MyCustomActivationStrategy>() when you override method WorkflowBase.Build(IWorkflowBuilder builder).

This way, when calling IWorkflowRuntime.CanStartWorkflowAsync(string definitionId, StartWorkflowRuntimeParams? options = default), the activation strategy you configured will be used to determine whether the workflow can be started or not.