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Workflow message passing - .NET SDK feature guide

This page shows how to do the following:

Signals​

How to develop with Signals using the Temporal .NET SDK

A Signal is a message sent to a running Workflow Execution.

Signals are defined in your code and handled in your Workflow Definition. Signals can be sent to Workflow Executions from a Temporal Client or from another Workflow Execution.

Define Signal​

How to define a Signal using the Temporal .NET SDK

A Signal has a name and can have arguments.

  • The name, also called a Signal type, is a string.
  • The arguments must be serializable. To define a Signal, set the [WorkflowSignal](https://dotnet.temporal.io/api/Temporalio.Workflows.WorkflowSignalAttribute.html) attribute on the Signal method inside your Workflow. A string name can be provided to the attribute, otherwise the Signal's name defaults to the unqualified method name (sans an "Async" suffix if it is async).

Temporal suggests taking a single argument that is an object that can be added to as needed.

[WorkflowSignal]
public async Task DoSomethingAsync(DoSomethingParam input) => pendingThings.Add(input);

Send a Signal from a Temporal Client​

How to send a Signal from a Temporal Client using the Temporal .NET SDK

When a Signal is sent successfully from the Temporal Client, the WorkflowExecutionSignaled Event appears in the Event History of the Workflow that receives the Signal.

To send a Signal from the Client, use the SignalAsync() method on the Workflow handle. The Workflow handle can be obtained via StartWorkflowAsync() or GetWorkflowHandle() methods on the client.

var client = await TemporalClient.ConnectAsync(new("localhost:7233"));
var handle = await client.StartWorkflowAsync(
    (MyWorkflow wf) => wf.RunAsync(),
    new(id: "my-workflow-id", taskQueue: "my-task-queue"));
var param = new DoSomethingParam("something");
await handle.SignalAsync(wf => wf.DoSomethingAsync(param));

Send a Signal from a Workflow​

How to send a Signal from a Workflow using the Temporal .NET SDK

A Workflow can send a Signal to another Workflow, in which case it's called an External Signal.

When an External Signal is sent:

Use GetExternalWorkflowHandle to get a Workflow handle to an existing Workflow by its identifier.

var handle = Workflow.GetExternalWorkflowHandle<OtherWorkflow>("other-workflow-id");
var param = new DoSomethingParam("something");
await handle.SignalAsync(wf => wf.DoSomethingAsync(param));

Signal-With-Start​

How to Signal-With-Start using the Temporal .NET SDK

Signal-With-Start is used from the Client. It takes a Workflow Id, Workflow arguments, a Signal name, and Signal arguments.

If there's a Workflow running with the given Workflow Id, it will be signaled. If there isn't, a new Workflow will be started and immediately signaled.

To send a Signal-With-Start in .NET, set the StartSignal property in WorkflowOptions for StartWorkflowAsync or ExecuteWorkflowAsync with the name of your Signal. Arguments for the signal can be set with the StartSignalArgs. A SignalWithStart helper exists on the options for type-safe invocation.

var client = await TemporalClient.ConnectAsync(new("localhost:7233"));

// Create options for signal-with-start
var options = new WorkflowOptions(id: "my-workflow-id", taskQueue: "my-task-queue");
var param = new DoSomethingParam("something");
options.SignalWithStart((MyWorkflow wf) => wf.DoSomethingAsync(param));
await client.StartWorkflowAsync((MyWorkflow wf) => wf.RunAsync(), options);

Dynamic Handler​

How to set a Dynamic Handler

Temporal supports Dynamic Signals, Queries, Workflows, and Activities, These are unnamed handlers that are invoked if no other statically defined handler with the given name exists.

Dynamic Handlers provide flexibility to handle cases where the names of Signals, Queries, Workflows, or Activities, aren't known at run time.

caution

Dynamic Handlers should be used judiciously as a fallback mechanism rather than the primary approach. Overusing them can lead to maintainability and debugging issues down the line.

Instead, Signals, Queries, Workflows, or Activities should be defined statically whenever possible, with clear names that indicate their purpose. Use static definitions as the primary way of structuring your Workflows.

Reserve Dynamic Handlers for cases where the handler names are not known at compile time and need to be looked up dynamically at runtime. They are meant to handle edge cases and act as a catch-all, not as the main way of invoking logic.

Set a Dynamic Signal​

How to set a Dynamic Signal using the Temporal .NET SDK

A Dynamic Signal in Temporal is a Signal that is invoked dynamically at runtime if no other Signal with the same input is registered. A Signal can be made dynamic by setting Dynamic to true on the [WorkflowSignal] attribute. Only one Dynamic Signal can be present on a Workflow.

The Signal Handler parameters must accept a string name and Temporalio.Converters.IRawValue[] for the arguments. The Workflow.PayloadConverter property is used to convert an IRawValue object to the desired type using extension methods in the Temporalio.Converters namespace.

[WorkflowSignal(Dynamic = true)]
public async Task DynamicSignalAsync(string signalName, IRawValue[] args)
{
    var input = Workflow.PayloadConverter.ToValue<DoSomethingParam>(args.Single());
    pendingThings.Add(input);
}

Queries​

A Query is a synchronous operation that is used to get the state of a Workflow Execution.

Define a Query​

How to define a Query using the Temporal .NET SDK

A Query has a name and can have arguments.

  • The name, also called a Query type, is a string.
  • The arguments must be serializable.

Queries may be methods or properties (only the getter is used). Queries must be synchronous and must not mutate workflow state in any way or issue any Commands. To define a Query, set the [WorkflowQuery](https://dotnet.temporal.io/api/Temporalio.Workflows.WorkflowQueryAttribute.html) attribute on the Query method or property inside your Workflow. A string name can be provided to the attribute, otherwise the Query's name defaults to the unqualified method/property name.

Queries can be methods that can accept arguments:

[WorkflowQuery]
public string GetMyStatus(MyStatusParam input) => statuses[input.Type];

Or properties:

[WorkflowQuery]
public string MyStatus { get; private set; }

Send a Query from a Temporal Client​

How to send a Query using the Temporal .NET SDK

Queries are sent from a Temporal Client.

To send a Query to a Workflow Execution from Client code, use the QueryAsync() method on the Workflow handle.

var client = await TemporalClient.ConnectAsync(new("localhost:7233"));
var handle = await client.StartWorkflowAsync(
    (MyWorkflow wf) => wf.RunAsync(),
    new(id: "my-workflow-id", taskQueue: "my-task-queue"));
var status = await handle.QueryAsync(wf => wf.MyStatus);

Set a Dynamic Query​

How to set a Dynamic Query using the Temporal .NET SDK

A Dynamic Query in Temporal is a Query method that is invoked dynamically at runtime if no other Query with the same name is registered. A Query can be made dynamic by setting Dynamic to true on the [WorkflowQuery] attribute. Only one Dynamic Query can be present on a Workflow.

The Query Handler parameters must accept a string name and Temporalio.Converters.IRawValue[] for the arguments. The Workflow.PayloadConverter property is used to convert an IRawValue object to the desired type using extension methods in the Temporalio.Converters namespace.

[WorkflowQuery(Dynamic = true)]
public string DynamicQueryAsync(string queryName, IRawValue[] args)
{
    var input = Workflow.PayloadConverter.ToValue<MyStatusParam>(args.Single());
    return statuses[input.Type];
}

Updates​

How to develop with Updates using the Temporal .NET SDK

An Update is an operation that can mutate the state of a Workflow Execution and return a response.

Define an Update​

How to define an Update using the Temporal .NET SDK

Workflow Updates handlers are methods in your Workflow Definition designed to handle updates. These updates can be triggered during the lifecycle of a Workflow Execution.

Define an Update Handler

To define an update handler, use the [WorkflowUpdate] attribute on a method within your Workflow.

  • Attribute Usage: Apply [WorkflowUpdate] to the method intended to handle updates.
  • Overriding: If a method with this attribute is overridden, the overriding method should also have the [WorkflowUpdate] attribute.
  • Validator Method: Optionally, you can define a validator method for the update handler. This validator is specified using [WorkflowUpdateValidator] attribute with the argument of the update method (e.g. [WorkflowUpdateValidator(nameof(MyUpdateMethod))]) and is invoked before the update handler.
  • Return Values: The update handler can return a serializable value. This value is sent back to the caller of the update.
[WorkflowUpdate]
public async Task<string> UpdateStatusAsync(Status status)
{
    this.status = status;
    return "Status updated";
}

Send an Update from a Temporal Client​

How to send an Update from a Temporal Client using the Temporal .NET SDK

To send a Workflow Update from a Temporal Client, call the ExecuteUpdateAsync method on the WorkflowHandle class.

var result = await handle.ExecuteUpdateAsync(wf => wf.UpdateStatusAsync(newStatus));