Event Trigger Payload | Hasura GraphQL Docs (original) (raw)

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
}

• Postgres
• MSSQL

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

Note

• In case of UPDATE, the events are delivered only if new data is distinct from old data. Thecomposite type comparisonis 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

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"
    }
  }
}

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 usereq.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.

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.