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Event Trigger Payload

Introduction

Whenever data-driven events invoke an Event Trigger, the payload of the event is delivered to the webhook endpoint you provide. The payload contains information about the event that was triggered, including the new or updated data, and — when used with PostgreSQL — the session variables of the user who triggered the event.

HTTP request method

Event Triggers are invoked using an HTTP POST request with the following headers:

Content-Type: application/json

JSON payload

In the request object, the payload makes up the majority of the content. The payload is a JSON object with the following structure:

{
  // Headers above are not shown
  "payload": {
    "created_at": "<TIMESTAMP>",
    "delivery_info": {
      "current_retry": "<RETRY_NUMBER>",
      "max_retries": "<MAX_RETRIES>"
    },
    "event": {
      "data": {
        "new": "<OBJECT_OF_COLUMNS_AND_VALUES>",
        "old": "<OBJECT_OF_COLUMNS_AND_VALUES|NULL>"
      },
      "op": "<INSERT|UPDATE|DELETE|MANUAL>",
      "session_variables": {
        "x-hasura-role": "<ROLE_NAME>"
      },
      "trace_context": {
        "span_id": "<SPAN_ID>",
        "trace_id": "<TRACE_ID>"
      }
    },
    "id": "<UUID_FOR_INVOCATION>",
    "table": {
      "name": "<TABLE_NAME>",
      "schema": "<SCHEMA_NAME>"
    },
    "trigger": {
      "name": "<TRIGGER_NAME>"
    }
  }
  // Version below is not shown
}

Below, you'll find examples of the new and old objects for each operation type.

• INSERT
  • event.data.old will be null
  • event.data.new will contain the insert row
• UPDATE
  • event.data.old will be values before the update
  • event.data.new will contain the values after the update
• DELETE
  • event.data.old will contain the row that is deleted
  • event.data.new will be null
• MANUAL
  • event.data.old will be null
  • event.data.new will contain the current row

:::info Note

• In case of UPDATE, the events are delivered only if new data is distinct from old data. The composite type comparison is used to compare the old and new rows. If rows contain columns, which cannot be compared using <> operator, then internal binary representation of rows by Postgres is compared.
• Table computed fields are not included in the Event Trigger payload data

:::

Below, you'll find examples of the new and old objects for each operation type.

• INSERT
  • event.data.old will be null
  • event.data.new will contain the insert row
• UPDATE
  • If a row is updated and the primary key is also updated
    • event.data.old will be null
    • event.data.new will contain the values after the update
  • If a row is updated and the primary key is unchanged
    • event.data.old will be values before the update
    • event.data.new will contain the values after the update
• DELETE
  • event.data.old will contain the row that is deleted
  • event.data.new will be null
• MANUAL
  • event.data.old will be null
  • event.data.new will contain the current row

:::info Note

• In case of UPDATE, the events are delivered only if new data is distinct from old data. We use the primary keys to join the temporary tables inserted and deleted tables to correlate the old and new data.
• UPDATE event triggers will only work on tables which have primary keys.
• Since we use the primary key to co-relate DELETED and INSERTED table, if the primary key is updated then it is not possible to correlate the old and new data. Hence, only new data is sent in this case.

:::

Example

Below, we have an example of the payload for an INSERT operation.

{
  "payload": {
    "created_at": "2020-07-29T10:00:00.000Z",
    "delivery_info": {
      "current_retry": 0,
      "max_retries": 0
    },
    "event": {
      "data": {
        "new": {
          "id": 1,
          "name": "John"
        },
        "old": null
      },
      "op": "INSERT",
      "session_variables": {
        "x-hasura-role": "admin"
      },
      "trace_context": {
        "span_id": "123",
        "trace_id": "456"
      }
    },
    "id": "123e4567-e89b-12d3-a456-426614174000",
    "table": {
      "name": "users",
      "schema": "public"
    },
    "trigger": {
      "name": "insert_user"
    }
  }
}

:::info Parsing the payload

You can access data from the request by parsing the JSON payload. For example, to access the new user's id, you can use req.body.event.data.new.id to get the value 1.

:::

Webhook response structure

A 2xx response status code is deemed to be a successful invocation of the webhook. Any other response status will be deemed as an unsuccessful invocation which will cause retries as per the retry configuration.

After executing your business logic in the webhook, it's recommended that you return a JSON object in your webhook's response.

Retry-After header

If the webhook response contains a Retry-After header, then the event will be redelivered once more after the duration (in seconds) found in the header. Note that the header will be respected only if the response status code is non-2xx.

The Retry-After header can be used for retrying/rate-limiting/debouncing your webhook triggers.