How generate a workflow in runtime with elsa workflow - asp.net-core

Question

With Elsa workflow designer possible to define a workflow and publish it, also can make a workflow programmatically by implementing the IWorkflow interface.
I need to make programmatically workflow at runtime, save it on the database and run it sometimes.
in the asp.net core project controller, I resolve IWorkflowBuilder as a dependency and make a workflow with WorkflowBuilder and return a WorkFlowblueprint object, but I don't know how I can store it and how to run it?
I also have Elsa dashboard on my project and I use EntityFramework Persistence for it.
Is there a way to convert a WorkflowBluePrint to WorkFlowDefination or generate WorkflowDefination from scratch programmatically?
Does everyone have any idea?

Answer 1

Although it might theoretically be possible to store an IWorkflow implementation in the database, there are some caveats that make this tricky to say the least. Here is why:
A workflow definition created by the designer consists purely of a list of activities and connections between them. Because of that, everything is easily serialized into JSON and stored in the database.
However, when you write a C# class, you can do more fancy things, such as configuring activities using C# lambda expressions and implement "inline" activity code. When you try to serialize this to JSON, these C# expressions will be serialized using just their type names.
Although there might be ways to somehow store a programmatic workflow into the database, perhaps even by storing a compiled assembly in the DB, I don't think it's worth the trouble because there are better ways.
You said that you need a programmatic workflow that you only run sometimes.
To achieve that, you do not need to store a workflow in the database.
The way Elsa works is that all workflow sources are converted into a thing called a Workflow Blueprint.
A workflow blueprint is what represents an executable workflow where all the necessary details are dehydrated that the workflow invoker can use.
There are different "sources" to establish these workflow blueprints by means of classes that implement IWorkflowProvider, of which there are three:
Programmatic Workflow Provider
Database Workflow Provider
Blob Storage Workflow Provider
The programmatic provider is what turns IWorkflow implementations into workflow blueprints, while the database provider turns workflow definitions into blueprints. The blob storage provider is similar, except it turns JSON files into blueprints.
The bottom line is that the origin of a workflow blueprint doesn't matter for the workflow engine.
All workflow blueprints are accessed through a service called the workflow registry, which you can use to load & execute a given workflow.
For example, if you have a programmatic workflow called MyWorkflow, you can execute it whenever you want like this:
public class MyWorkflow : IWorkflow
{
public void Build(IWorkflowBuilder builder)
{
builder.WriteLine("Hello World!");
}
}
[ApiController]
[Route("my-workflow")]
public class MyWorkflowController : Controller
{
private readonly IWorkflowRegistry _workflowRegistry;
private readonly IStartsWorkflow _workflowStarter;
public MyWorkflowController(IWorkflowRegistry workflowRegistry, IStartsWorkflow workflowStarter)
{
_workflowRegistry = workflowRegistry;
_workflowStarter = workflowStarter;
}
[HttpGet("run")]
public async Task<IActionResult> RunMyWorkflow(CancellationToken cancellationToken)
{
// 1. Get my workflow blueprint.
var myWorkflowBlueprint = (await _workflowRegistry.GetWorkflowAsync<MyWorkflow>(cancellationToken))!;
// 2. Run the workflow.
await _workflowStarter.StartWorkflowAsync(myWorkflowBlueprint, cancellationToken: cancellationToken);
return Ok();
}
}
Invoking this controller will execute MyWorkflow.
As you can see, there is no need to store the workflow in the database in order to be able to execute it on demand. Even if you did store the workflow in the database, the code would be the same, provided that the name of the workflow remains "MyWorkflow". Under the covers, the GetWorkflowAsync<TWorkflow> is simply an extension method that uses the type name to find the workflow by name. If you wanted to load a workflow by name for which there's no workflow class defined, you would simply use FindByNameAsync, or FindAsync if all you had is a workflow definition ID.