Extract EdgeX Message Bus Metadata Using the Meta Function

When EdgeX Foundry publishes device readings to the message bus, events include metadata such as creation timestamps, device identifiers, and correlation tags. This guide describes how to extract event and reading metadata using the rekuiper meta() function.

EdgeX Message Bus Data Model

EdgeX Foundry packages device data into hierarchical Event structures containing metadata and an array of Reading objects:

• Event Structure:
  • ID: Event identifier.
  • DeviceName: Name of the originating device.
  • ProfileName: Associated device profile name.
  • SourceName: Source command or event name.
  • Origin: Nanosecond timestamp recorded at creation.
  • Tags: Key-value metadata tags.
  • Readings: Array of sensor values:
    • Id: Reading identifier.
    • Origin: Reading timestamp.
    • DeviceName: Sensor device name.
    • ResourceName: Sensor metric name (for example: temperature).
    • ProfileName: Metric profile name.
    • ValueType: Data type identifier.
    • Value: Sensor reading value.

Schema Changes in EdgeX v2

When migrating from EdgeX v1:

1. EdgeX v2 removes the Pushed, Created, and Modified metadata fields.
2. The Device field is renamed to DeviceName in both events and readings.
3. The Name field of readings is renamed to ResourceName.

EdgeX Metadata Resolution in rekuiper

rekuiper ingests EdgeX bus events and maps top-level sensor values directly to stream columns. The engine preserves event and reading metadata inside an internal tuple accessible through meta().

1. Define an EdgeX stream named events:

2. When devices publish events to the message bus:
   • Metric values (temperature, humidity) become queryable columns.
   • Event and reading headers become metadata attributes.

3. Query columns and extract metadata attributes in SQL:

Extracting Event-Level Metadata

Pass the field name directly into meta():

• meta(deviceName): Returns DeviceName from the Event header.
• meta(origin): Returns Origin creation timestamp from the Event header.

Extracting Reading-Level Metadata

Extract reading metadata using the arrow syntax: reading_name -> property:

• meta(temperature -> origin): Returns Origin for the temperature reading.
• meta(humidity -> id): Returns reading Id for the humidity reading.

Assigning Column Aliases in SELECT Clauses

When extracting multiple metadata fields in the SELECT clause, assign explicit column aliases using AS to prevent field name collisions:

SELECT
  temperature,
  humidity,
  meta(id) AS eid,
  meta(origin) AS eo,
  meta(temperature->id) AS tid,
  meta(temperature->origin) AS torigin,
  meta(Humidity->deviceName) AS hdevice,
  meta(Humidity->profileName) AS hprofile
FROM demo
WHERE meta(deviceName) = "demo2"

Available Metadata Keys

Event Metadata Fields

id, deviceName, profileName, sourceName, origin, tags, correlationid.

Reading Metadata Fields

id, deviceName, profileName, origin, valueType.