Poll Trigger

Records (tickets, leads, items etc.) are called events in a poll. A poll trigger constantly executes a poll block for new events at fixed time intervals. This time interval depends on a user's subscription (5 or 10 minutes). At the same time, it is also able to support pagination. This is useful to prevent request timeouts when making requests with large response results. A trigger can execute immediate consecutive polls to retrieve events from successive pages.

There are two types of trigger. The classic trigger type is used by default if type is not specified. The other type is called the "paging_desc" trigger, which can be used only for endpoints that provide events sorted in descending order. This trigger type has an auto-paging mechanism that lets you build a simple and efficient trigger. (described in detail below)

A ruby hash is returned in each poll. This hash should contain a few keys. The array of events, or data, should be passed into the events key. At the same time, a cursor is saved in next_page/next_poll (depending on the trigger type). This cursor provides information about where the current poll stopped, and used in the next poll. A classic type trigger has an additional key can_poll_more, which can be defined to conditionally fire immediate polls for multi-page results.

Classic Trigger

No need to define any type to use the classic trigger. This type is usually used for APIs that only return responses sorted in ascending order.

updated_ticket: {
  input_fields: lambda do
    [
      {
        name: 'since',
        type: :timestamp,
        optional: false
      }
    ]
  end,

  poll: lambda do |connection, input, last_updated_since|
    page_size = 100
    updated_since = (last_updated_since || input['since']).to_time.utc.iso8601

    tickets = get("https://#{connection['helpdesk']}.freshdesk.com/api/v2/tickets.json").
              params(order_by: 'updated_at',
                     order_type: 'asc',
                     per_page: page_size,
                     updated_since: updated_since)

    next_updated_since = tickets.last['updated_at'] unless tickets.blank?

    {
      events: tickets,
      next_poll: next_updated_since,
      can_poll_more: tickets.length >= page_size
    }
  end,

  dedup: lambda do |ticket|
    ticket['id']
  end,

  output_fields: lambda do |object_definitions|
    object_definitions['ticket']
  end
}

poll

Arguments

A poll block is given 3 arguments.

The first argument is connection, used to access inputs from connection field values. This is frequently used to access domain or subdomain information from the user.

input provides access to trigger input field values from the recipe. Inputs like "created_since" a particular date is usually used in a trigger to allow filtering historic records. In this case, Knack does not provide filtering by record created dates, input is given an empty array.

The last argument, usually given the name last_updated_since or last_created_since, is the cursor "stored" from a previous poll. This is crucial to a good trigger design. It is used to determine where the last poll stopped and where to begin next. As an example, it is usually given the last (latest) "updated"/"created" time. When the trigger is first started, this value is nil.

Output
poll: lambda do |connection, input, last_updated_since|
  page_size = 100
  updated_since = (last_updated_since || input['since']).to_time.utc.iso8601

  tickets = get("https://#{connection['helpdesk']}.freshdesk.com/api/v2/tickets.json").
            params(order_by: 'updated_at',
                   order_type: 'asc',
                   per_page: page_size,
                   updated_since: updated_since)

  next_updated_since = tickets.last['updated_at'] unless tickets.blank?

  {
    events: tickets,
    next_poll: next_updated_since,
    can_poll_more: tickets.length >= page_size
  }
end

In a classic type trigger, the expected output contains events, next_poll and can_poll_more.

events expects an array of individual results to be processed through the recipe as individual events.

next_poll is a cursor that will be passed on to the successive poll (third argument of poll block.

Important: This trigger type does not have automatic-immediate polling. Immediate polling is determined by can_poll_more, which is a boolean value for whether an immediate poll should be made.

Example JSON response:

[
  {
    "id": 1,
    "updated_at": "2016-08-13T00:53:44Z"
  },
  {
    "id": 2,
    "updated_at": "2016-09-14T02:25:00Z"
  },
  ...
]

When a get request receives this JSON response, it looks up the array for the last record (latest record) and passes it as the cursor for the next poll. It also checks the response array size. If it is equal to the size limit, it is likely that there are more records matching this request in consequtive pages. Hence the expression given to can_poll_more evaluates to true and invokes an immediate successive poll. This loop continues until response array size is smaller than page limit.

At the end of the loop. The last (latest) created date is passed as next_poll. This value will be used in the next poll cycle to pick up new records.

dedup

Dedup block is used to identify individual events. It is given a single argument "event", which corresponds to individual elements in the records array passed into "events".

A typical dedup input is event[‘id’] where the event argument name can be replaced to make the code more readable. This should be used only in classic triggers.

dedup: lambda do |ticket|
  ticket["id"]
end

In some instances, a record needs to be proccessed as separate events. A typical scenario is updated records. To do this, append updated timestamp field to the dedup expression like so.

dedup: lambda do |ticket|
  ticket["id"] + "@" + ticket["updated_at"]
end

With this, 2 occurence of a record with the same "ID" but with different "updated_at" values will be recorded as separate events.

Descending Trigger

new_alert: {
  type: :paging_desc,

  input_fields: lambda do
    [
      {
        name: 'since',
        type: :timestamp,
        optional: false
      }
    ]
  end,

  poll: lambda do |connection, input, page|
    limit = 100
    page ||= 0
    created_since = (input['since'] || Time.now).to_i
    offset = (limit * page)

    response = get("https://api.pingdom.com/api/2.0/actions").
                 params(from: created_since,
                        limit: limit,
                        offset: offset)

    {
      events: response,
      next_page: (response.length >= limit) ? page + 1 : nil
    }
  end,

  document_id: lambda do |response|
    response['checkid']
  end,

  sort_by: lambda do |response|
    response['time']
  end,

  output_fields: lambda do |object_definitions|
    object_definitions['alert']
  end
}

type

type: :paging_desc - This type should be used only if results are in descending order. A paging_desc trigger works by assuming a descending order and continuously poll for all unique records. If the API is unable to return records in descending order, ignore this key to use the classic trigger.

A record of all event IDs (defined in document_id ) is recorded for each recipe. Each recipe will "remember" all event IDs that is processed through a trigger.

Based on assumption of order, the trigger can stop the polling cycle once a similar event IDs is observed. This is because further polls will return events "before" and would have already been processed by the trigger. At this point, the trigger stops polling and wait for the new poll cycle for new events. The Workato trigger framework handles deduplication in the background.

poll

Poll block is where you define how events are obtained. Typically, a GET request is used to retrieve a list of records to be processed as trigger events.

Arguments

Descending trigger polls have the exact same argument structure. connection, input and cursor. The one difference is that the last argument is usually given the name page. In a descending trigger, this argument is usually used to pass the page number instead of record timestamp.

Output

Similar to a classic trigger, the events in output here expects an array of results.

poll: lambda do |connection, input, page|
  limit = 100
  page ||= 0
  created_since = (input['since'] || Time.now).to_i
  offset = (limit * page)

  response = get("https://api.pingdom.com/api/2.0/actions").
               params(from: created_since,
                      limit: limit,
                      offset: offset)

  {
    events: response,
    next_page: (response.length >= limit) ? page + 1 : nil
  }
end

Instead of next_poll, paging_desc type trigger should be given next_page as cursor. It is used for passing the next page to be polled.

A typical response looks like this.

{
  "current": "https://api.sample.com/records?order=desc&from=2016-12-09T22%3A57%3A13Z&page=1",
  "next": "https://api.sample.com/records?order=desc&from=2016-12-09T22%3A57%3A13Z&page=2",
  "data": [
    {
      "checkid": 123,
      "time": "2016-12-13T19:09:01Z",
      ...
    },
    {
      "checkid": 124,
      "time": "2016-12-10T06:20:00Z",
      ...
    }
  ]
}

response["data"] is an array of results from the request, which should be passed to events. While it varies between APIs, most will provide some form of pointer to the next page of results. In this example,response["next"] is an API generated url to be used to retrieve the next page of results matching the request. Hence we can simply pass it to next_page. In the successive poll, this value is passed to the poll block and the next set of records is retrieved.

On the last page, response["next"] is usually null. In that case, it will cause the successive poll to make the same request as in the first page. When this happens, the trigger framework detects a duplicate event (mechanism for detection explained in detail later) and halts all immediate polls. At this point, the trigger goes to "sleep" until the next poll cycle.

New records being added in the cloud instance will appear in the first page of requests since records are returned in descending order. The trigger picks up new records and processes them until a duplicate event is detected, at which point it "sleeps". This trigger type depends on a descending order to retrieve only "new" records and stops upon detection of "old" records.

This way, the trigger polls for new records efficiently, without making any repeated requests to retrieve the entire set of records in each poll cycle.

document_id

Similar to dedup, paging_desc type triggers uses document_id to identify unique records. Write an expression that can uniquely identify the "ID" of records.

document_id: lambda do |event|
  event["checkid"]
end

Unlike classic triggers, there is no need to include timestamp fields into the document_id expression to deduplicate updated records. Descending triggers have an additional block sort_by to process this.

sort_by

In addition to document_id, this block is used to define the field that is used to sort records (in descending order). It could be "created_at" or "updated_at" or similar fields.

sort_by: lambda do |event|
  event["time"]
end

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