Recipes

Append to a List

Submit-and-review flows are everywhere: place an order, see it in the history; send an event, see it in the feed. This recipe accepts items with POST and returns everything submitted so far with GET, using flags as an append-only store.

The recipe

mock "POST /purchases" {
  format = "json"
  body = <<-EOF
    {{= $id (uuid)}}
    {{setFlag (append 'purchases:' $id) request.body}}
    {{= $ids (getFlag 'purchases:ids')}}
    {{#if $ids}}
      {{setFlag 'purchases:ids' (append $ids ',' $id)}}
    {{else}}
      {{setFlag 'purchases:ids' $id}}
    {{/if}}
    {
      "id": "{{$id}}",
      "status": "created"
    }
  EOF
}

mock "GET /purchases" {
  format = "json"
  body = <<-EOF
    {{= $ids (getFlag 'purchases:ids')}}
    [
      {{#if $ids}}
        {{#forEach (split $ids ',')}}
          {{json (getFlag (append 'purchases:' item))}}{{^isLast}},{{/isLast}}
        {{/forEach}}
      {{/if}}
    ]
  EOF
}

Try it

$curl -X POST http://localhost:8080/purchases -H 'Content-Type: application/json' -d '{"product": "Widget", "qty": 2}'

{ "id": "7d4c2f2e-9b1a-4f7e-8a3d-5e6f7a8b9c0d", "status": "created" }

$curl http://localhost:8080/purchases

[ { "product": "Widget", "qty": 2 } ]

How it works

Every submission gets a fresh id from the uuid helper, and the whole request body is stored as an object under purchases:<id>.
purchases:ids accumulates the ids as a comma-separated string. The first submission is the special case: appending to a missing flag would start the list with a comma, so the if branch sets it directly.
The GET splits the id list back into an array, looks each record up, and renders it with the json helper. The surrounding if keeps the response a valid empty array before anything is submitted.
POST mocks default to status 201, so no status field is needed.

Since nothing is ever removed, {{^isLast}},{{/isLast}} is safe here. If you add deletion, switch the list to the accumulator pattern from Stateful CRUD, which tolerates missing records.

Variations

Add a reset mock for test isolation: DELETE /purchases with {{delFlag 'purchases:ids'}} in the body.
Give entries a TTL by passing a third argument to both setFlag calls, and the feed cleans itself up after a while (combine with the accumulator pattern so expired records do not break commas).
Echo the stored item back with an id in each list entry by storing a composed object instead of the raw body; see the id note in Stateful CRUD.