Is it possible to specify a single children for more jobs using FlowProducer?

[paologf-mb]

Hello, using FlowProducer is it possible to specify a single children for more jobs?
For example (taking from the doc) instead of having this:

import { FlowProducer } from 'bullmq';
const flowProducer = new FlowProducer();

const queueName = 'assembly-line';
const chain = await flowProducer.add({
  name: 'car_engine',
  data: { },  // Some data
  queueName: 'engine',
  children: [{
      name: 'car_wheels',
      data: { },  // Some data
      queueName: 'wheels',
      children: [{ 
        name: 'car_chassis', 
        data: { },  // Some data
        queueName: 'chassis' 
       }],
    }],
});

, split the "wheels" step in 4 "wheel" steps that should start only after the "chassis" step and trigger the "engine" step.
So make chassis -> mount each wheel (separately but in parallel) -> add engine.
Something like this pseudo-code:

import { FlowProducer } from 'bullmq';
const flowProducer = new FlowProducer();

const queueName = 'assembly-line';

// Define a job that should be trigger just one time
const chassisJob =  new FlowJob({
  name: 'car_chassis',
  queueName: 'chassis',
  data: { },  // Some data
})
const chain = await flowProducer.add({
  name: 'car_engine',
  data: { },  // Some data
  queueName: 'engine',
  children: [
    { 
      name: 'car_wheel_1',
      queueName: 'wheels',
      data: { },  // Some data
      children: [ chassisJob ]
    },
    { 
      name: 'car_wheel_2',
      queueName: 'wheels',
      data: { },  // Some data
      children: [ chassisJob ]
    },
    { 
      name: 'car_wheel_3',
      queueName: 'wheels',
      data: { },  // Some data
      children: [ chassisJob ]
    },
    { 
      name: 'car_wheel_4',
      queueName: 'wheels',
      data: { },  // Some data
      children: [ chassisJob ]
    }],
});

, where is important that the chassisJob is launched only once and trigger each "wheels" queue.

Thanks

[manast]

What you are proposing is not possible, as one job cannot have more than 1 parent, however I am not sure why need this. In any case you could have a chassisJob that as last step in its processor function what it does is create a new Flow, something like this:

import { FlowProducer } from 'bullmq';
const flowProducer = new FlowProducer();

const queueName = 'assembly-line';

// Define a job that should be trigger just one time
const chassisJob =  new FlowJob({
  name: 'car_chassis',
  queueName: 'chassis',
  data: { },  // Some data
})

const chassisQueue = new Queue('chassis', ...);

const chassisWorker = new Worker('chassis', async (job) => {
  // Do something

  const chain = await flowProducer.add({
    name: 'car_engine',
    data: { },  // Some data
    queueName: 'engine',
    children: [
      { 
        name: 'car_wheel_1',
        queueName: 'wheels',
        data: { },  // Some data
      },
      { 
        name: 'car_wheel_2',
        queueName: 'wheels',
        data: { },  // Some data
      },
      { 
        name: 'car_wheel_3',
        queueName: 'wheels',
        data: { },  // Some data
      },
      { 
        name: 'car_wheel_4',
        queueName: 'wheels',
        data: { },  // Some data
      }],
  });
})

});