Relationships

Random customer ids are not useful if they point to people who were never generated. ref() lets one generator select a real event from another generator.

The result we want

The id and name on an order must come from the same earlier customer:

{"customerId":"CUST-00","name":"Paul Considine"}
{"orderId":"ORD-00","customerId":"CUST-00","customerName":"Paul Considine","item":"Wireless headphones"}

Select a generated customer

Each order selects a customer event that already exists. You do not need a schedule for this: ref(customers) tells Synthtraffic that orders depends on customers, so it creates source history before the first order is evaluated.

Orders that belong to existing customers

defaults:
  seed: 42

generators:
  - name: customers
    config:
      maxEvents: 2
    value:
      customerId: =seq(format=CUST-%02d)
      name: =faker(person.fullName)

  - name: orders
    config:
      maxEvents: 2
    vars:
      customer: =ref(customers)
    value:
      orderId: =seq(format=ORD-%02d)
      customerId: $customer.customerId
      customerName: $customer.name
      item: Wireless headphones

Press Try it. A customer appears before the first order. The streams can then continue together, and every order uses a customerId and customerName from a customer generated earlier.

How the relationship is built

1. ref(customers) tells Synthtraffic that customer events must exist first.
2. Synthtraffic generates and retains a customer before evaluating the first order.
3. ref(customers) selects one complete retained customer event.
4. vars.customer keeps that selected record available while the order is built.
5. $customer.customerId and $customer.name copy matching fields into the order.

Keeping the complete customer in vars matters: the id and name always come from the same person.

The scenario uses seed: 42, so the generated names and customer selections repeat on another run.

ref versus previous

• Use ref(customers) for an event from another generator.
• Use previous() for the earlier event from the same generator.

ref() cannot point at its own generator. ref and previous covers field paths, selection options, and same-stream examples.

You only need a schedule when you want stronger ordering—for example, finishing all customers before the first order. The automatic ordering from ref() is enough when each order only needs an existing customer.

Next: control generator order with schedules.