# Temporal

# Feature

Temporal (opens new window) lets you write complex asynchronous distributed workflows using easy to read linear code. For more information about Temporal take a look at the documentation here (opens new window).

The @tsed/temporal module allows you to decorate classes with @Temporal and corresponding methods with @Activity to write and start asynchronous workflows.

Inject the TemporalClient to start/schedule and query workflows or to send signals to them.

Use the bootstrapWorker helper to start a queue that executes your workflows and activities.

# Installation

To begin, install the Temporal module for Ts.ED:

npm install --save @tsed/temporal
npm install --save @temporalio/client @temporalio/worker

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# Configure your server

Import @tsed/temporal in your Server:

import {Configuration} from "@tsed/common";
import "@tsed/temporal"; // import temporal ts.ed module

@Configuration({
  temporal: {
    enabled: true,
    connection: {
      /* optional: see ConnectionOptions of @temporalio/client */
    },
    client: {
      /* optional: see ClientOptions of @temporalio/client */
    }
  }
})
export class Server {}

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# Create a new Service

Decorate the class with @Temporal.

Use the @Activity decorator to define activities.

import {Temporal, Activity} from "@tsed/agenda";

@Temporal()
export class UserOnboardingActivities {
  constructor(private userService: UserService, private emailService: EmailService) {}

  @Activity()
  async sendVerificationEmail(email: string) {
    return this.emailService.sendVerificationEmail(email);
  }

  @Activity()
  async activateUser(email: string) {
    return this.userService.activateUser(email);
  }

  @Activity()
  async sendWelcomeEmail(email: string) {
    return this.emailService.sendWelcomeEmail(email);
  }

  @Activity()
  async sendFollowUpEmail(email: string) {
    return this.emailService.sendFollowUpEmail(email);
  }

  @Activity()
  async deleteUser(email: string) {
    return this.userService.deleteUser(email);
  }
}

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Optional, create an interface for your activities to use it later for your workflows (opens new window).

interface IUserOnboardingActivities {
  sendVerificationEmail(email: string): Promise<void>;
  activateUser(email: string): Promise<void>;
  sendWelcomeEmail(email: string): Promise<void>;
  sendFollowUpEmail(email: string): Promise<void>;
  deleteUser(email: string): Promise<void>;
}

export type Activities = IGreetingActivity;

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# Write Workflows

Workflows are regular functions that cannot interact directly with Ts.ED or other packages. Just the earlier created interface is used for type-safety.

WARNING

Do not import any non temporal packages here. The workflows are bundled internally by the worker and won't have access to anything else.

import {proxyActivities, defineSignal, setHandler, condition, sleep} from "@temporalio/workflow";
import {Activities} from "../activities";

export const isVerifiedSignal = defineSignal("verificationSignal");

export async function onboardUser(email: string): Promise<string> {
  const {sendVerificationEmail, activateUser, sendWelcomeEmail, sendFollowUpEmail, deleteUser} = proxyActivities<Activities>({
    startToCloseTimeout: "1 minute"
  });

  let isVerified = false;
  setHandler(isVerifiedSignal, () => {
    isVerified = true;
  });

  // 1. Send verification email
  await sendVerificationEmail(email);

  // 2. Wait for verification ...
  const verifiedInTime = await condition(() => isVerified, "1w" /* or for a timeout */);
  if (!verifiedInTime) {
    // 3a. If not verified in time, delete user
    await deleteUserAndTenant(email);
    return false;
  }

  // 3b. If verified in time, send welcome email
  await sendWelcomeEmail(email);

  // 4. Send follow up email after one day
  await sleep("1d"); // special sleep function by temporal
  await sendFollowUpEmail(email);
}

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# Inject TemporalClient

Inject the TemporalClient instance to interact with it directly, e.g. to start a workflow.

import {Service, AfterRoutesInit} from "@tsed/common";
import {TemporalClient} from "@tsed/temporal";
import {onboardUser} from "../workflows";

@Service()
export class UsersService implements AfterRoutesInit {
  @Inject()
  private temporalClient: TemporalClient;

  async create(user: User): Promise<User> {
    // ...
    await this.temporalClient.workflow.start(onboardUser, {
      args: [user.email],
      taskQueue: "onboarding",
      workflowId: `onboarding-${user.id}`
    });
  }
}

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# Start a worker

The workflows and activities won't get executed until you start a worker. This module provides a helper function to bootstrap a worker based on your Ts.ED server class that is aware of all your activities.

The most tricky part is the workflowsPath parameter. This is the path of the file/folder where the workflows are exported. The file is automatically loaded when the worker is started and internally bundled with webpack. The path is highly dependent on your project structure and build process.

Read more about it here (opens new window).

import {bootstrapWorker} from "@tsed/temporal";
import {Server} from "./app/Server";

const worker = await bootstrapWorker(Server, {
  worker: {
    taskQueue: "onboarding",
    workflowsPath: require.resolve("./temporal") // other example: path.join(process.cwd(), 'dist/apps/api/temporal/index.ts');
  },
  connection: {
    /* optional: see NativeConnectionOptions of @temporalio/worker */
  },
  platform: {
    /* optional: see PlatformBuilderSettings of @tsed/common */
    componentsScan: false,
    logger: {
      level: "info"
    }
  }
});
await worker.run();

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