Component Configuration Variables

In certain scenarios, it’s necessary to uniformly modify component configurations or dynamically replace them during component runtime. You can achieve this by using built-in variables to substitute component configurations. The syntax is as follows: ${key} or ${key.subKey}.

Global Variables

Global variables are executed for replacement logic during component initialization (when the component's Init method is executed), including the following variables:

• global variable: Access values from config.Properties, for example, ${global.key}.
• vars variable: Access values from rule chain vars, for example, ${vars.key}.

Global Variables: All component configuration fields support variable substitution.

Runtime Variables

Runtime Variables are executed for replacement logic during component runtime (when the component's OnMsg method is executed), including the following variables:

• id variable: Access the message ID.
• ts variable: Access the message timestamp.
• data variable: Access the original message content.
• msg variable: Access the transformed message data. If the message's dataType is JSON, you can access fields using ${msg.key}.
• metadata variable: Access message metadata, e.g., ${metadata.key}.
• msgType variable: Access the message type.
• dataType variable: Access the data type.
• nodeId variable: v0.33.0+ Cross-node variable for accessing output data from specified nodes. Examples: ${node1.msg.temperature}, ${node1.metadata.deviceId}, ${node1.msgType}, etc.

Runtime Variables: Only specific component configuration fields, as indicated, support variable substitution.

Cross-Node Variables Details

Cross-node variables allow accessing output data from any previously executed node in the rule chain within component configurations. The syntax format is: ${nodeId.field}

Supported fields include:

• ${nodeId.msg}: Access the message content of the specified node
• ${nodeId.msg.fieldName}: Access specific fields in the specified node's message (when message is in JSON format)
• ${nodeId.metadata}: Access the metadata of the specified node
• ${nodeId.metadata.key}: Access specific key-value pairs in the specified node's metadata
• ${nodeId.msgType}: Access the message type of the specified node
• ${nodeId.dataType}: Access the data type of the specified node
• ${nodeId.id}: Access the message ID of the specified node
• ${nodeId.ts}: Access the message timestamp of the specified node

Note: Cross-node variables require the target node to have completed execution and produced output. During rule chain initialization, if cross-node variables in the format ${nodeId.xx.xx} are detected in component configurations, corresponding dependency relationships will be automatically established to ensure data availability.

Examples

Basic Variables Example

{
  "ruleChain": {
	"id":"rule01",
    "name": "test",
    "configuration": {
      "vars": {
        "topicPrefix":"/device/msg"
      }
    }
  },
  "metadata": {
    "nodes": [
      {
        "id": "s2",
        "type": "mqttClient",
        "name": "push data",
        "configuration": {
          "server": "${global.mqttServer}",
          "topic": "${vars.topicPrefix}/${metadata.deviceId}"
        }
      }
    ],
    "connections": [
      {
      }
    ]
  }
}

Cross-Node Variables Example

Note: Cross-node variables can only be used in component configuration fields that support runtime variable substitution, such as mqttClient's topic, restApiCall's url, dbClient's sql, functions's functionName, etc. The jsScript field of jsTransform/jsFilter/log nodes does not support ${...} runtime variable substitution.

{
  "ruleChain": {
    "id": "rule02",
    "name": "cross-node-example"
  },
  "metadata": {
    "nodes": [
      {
        "id": "sensor1",
        "type": "jsTransform",
        "name": "Sensor Data Processing",
        "configuration": {
          "jsScript": "msg.temperature = 25.5; msg.humidity = 60; return {msg: msg, metadata: metadata, msgType: msgType};"
        }
      },
      {
        "id": "sensor2",
        "type": "jsTransform",
        "name": "Another Sensor",
        "configuration": {
          "jsScript": "msg.pressure = 1013.25; return {msg: msg, metadata: metadata, msgType: msgType};"
        }
      },
      {
        "id": "publisher",
        "type": "mqttClient",
        "name": "Publish Combined Data",
        "configuration": {
          "server": "${global.mqttServer}",
          "topic": "/sensor/combined/${sensor1.msg.temperature}/${sensor2.msg.pressure}"
        }
      }
    ],
    "connections": [
      {
        "fromId": "sensor1",
        "toId": "publisher",
        "type": "Success"
      },
      {
        "fromId": "sensor2",
        "toId": "publisher",
        "type": "Success"
      }
    ]
  }
}