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Using Typescript Objects

You can use class instance methods as workflows and steps. Any class instance method can be freely used as a step using the DBOS.step decorator or DBOS.runStep; there are no special requirements. To use a class instance method as a workflow, you must use the DBOS.workflow decorator and the class must inherit from ConfiguredInstance. For example:

class MyClass extends ConfiguredInstance {
  cfg: MyConfig;
  constructor(name: string, config: MyConfig) {
    super(name);
    this.cfg = cfg;
  }

  override async initialize() : Promise<void> {
    // ... Validate this.cfg; will be called at DBOS.launch()
  }

  @DBOS.workflow()
  async testWorkflow(p: string): Promise<void> {
    // ... Operations that use this.cfg
  }
}

const myClassInstance = new MyClass('instanceA');

When you create a new instance of such a class, the constructor for the base ConfiguredInstance must be called with a name. This name must be unique among instances of the same class. Additionally, all ConfiguredInstance classes must be instantiated before DBOS.launch() is called.

The reason for these requirements is to enable workflow recovery. When you create a new instance of, DBOS stores it in a global registry indexed by name. When DBOS needs to recover a workflow belonging to that class, it looks up the name so it can run the workflow using the right class instance. While names are used by DBOS Transact internally to find the correct object instance across system restarts, they are also potentially useful for monitoring, tracing, and debugging.

Using Configured Class Instances​

Configured class instances should be created and named when the application starts, before any workflows run. This ensures that they will all be initialized before any processing begins.

Writing New Configured Classes​

All configured classes:

  • Extend from the ConfiguredInstance base class
  • Provide a constructor, which can take any arguments, but must provide a name to the base ConfiguredInstance constructor
  • May have an initialize() method that will be called after all objects have been created, but before request handling commences

initialize() Method​

The initialize() method will be called during application initialization, after the code modules have been loaded, but before request and workflow processing commences. DBOS is available during initialize. Any validation of connection information (complete with diagnostic logging and reporting of any problems) should be performed in initialize().

Notes​

Event registration decorators such as @DBOS.scheduled cannot be applied to instance methods.