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Twin Property
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Twin Property Tutorial

This tutorial provides information on how to use the TwinProperty module of SDK to subscribe to changes in Desired properties and write the Reported properties. It uses Redis as the data store. The properties must be associated to a Group Name.

This module allows more than 1 Edge application to access the same Group Name and Desired property with Redis acting as the shared repository for information.

Namespace: Agora.Edge

A singleton member of Agora.SDK called Twin is used by applications to interact with twin properties.

Configuration

The module uses Redis as the data store, hence, has dependency on the SDK's Redis module. The Edge application must have the following configuration in its primary configuration file

{
    "AEA2":{
        "RedisClient": {
            "Server": "localhost",
            "Port": 6379,
        }
    }
}

Additionally, the application should connect to Redis using Redis.Connect() method.

NET

Properties:

  • Instance: TwinProperty - Used to access the singleton instance and is the same as using the Agora.SDK.TwinProperty.

Event

  • ChangeEvent - Used to subscribe/unsubscribe to a Desired property or a Group Name

Methods:

  • public bool SetReportedProperty(string propName, string propValue, string tpId) - Method to set reported property of name propName associated to group name tpId with value propValue. The method uses redis key pattern as mentioned below. :-
twin_properties/{tpId}/reported/{propName}
twin_properties/{tpId}/reported/__appname
  • public string GetDesiredProperty(string propName, string tpId) - Method to read the value of a desired property i.e. propName associated to a GroupName tpId. The method uses the key pattern as mentioned below.:-
twin_properties/{tpId}/desired/{propName}
  • public string GetReportedProperty(string propName, string tpId) - Method to read the value of a reported property propName assoicated to group name tpId. The method uses key pattern as mentioned below:-
twin_properties/{tpId}/reported/{propName}

Python

  • def observe(app_callback:Any, tp_group_id:str, property_name:str=None) - Method to add observable for tp_group_id and property_name. If property_name set to None, observable is set for Redis Key pattern:
twin_properties/{tp_group_id}/desired/*
  • def stop_observe(tp_group_id:str,property_name:str=None) - Method to remove observable for tp_group_id and property_name if it exists. If property_name set to None, observable is removed for the pattern:
twin_properties/{tp_group_id}/desired/*
  • def set_reported_property(prop_name:str, prop_value:any, tp_group_id:str): - Method to set reported property. The method uses redis key as mentioned below. :-
twin_properties/{tp_group_id}/reported/
twin_properties/{tp_group_id}/reported/__appname
  • def get_desired_property(prop_name:str, tp_group_id:str): - Method to read the value of a desired property i.e. prop_name. The method uses the key pattern as mentioned below. :-
twin_properties/{tp_group_id}/desired/
  • def get_reported_property(prop_name:str, tp_group_id): - Method to read the value of a reported property prop_name. The method uses key pattern as mentioned below:-
twin_properties/{tp_group_id}/reported/

For Local Development and Testing

NET

Create a Simple Console .NET Application

using System.Text.Json;
using static Agora.SDK;

namespace redis_sdk_project
{
   public class Program
   {
       public static void appCallback(string groupId, Dictionary<string, string> data)
       {
           foreach (var kvp in data)
           {
               $"AppCallback called for group {groupId} and the Key: {kvp.Key}, and Value: {kvp.Value}\n".LogInfo();
           }
       }

       public static void Main(string[] args)
       {
           Redis.Connect(30);
           var propName = "TwinPropName";
           var tpGroupId = "Group2";
           //Add subscription to all desired properties associated to a GroupName
           Twin["Group1"].ChangeEvent += appCallback;        
           //Add subscription to a particular desired property associated to a GroupName
           Twin["Group2"][propName].ChangeEvent += appCallback2;            
           //Set reported Property
           Twin.SetReportedProperty(propName, "30", tpGroupId);
           //Get desired property value
           $"Desired Property:{propName}- {Twin.GetDesiredProperty(propName, tpGroupId)}".LogInfo();
           //Get reported property
           $"Reported Property:{propName}- {Twin.GetReportedProperty(propName, tpGroupId)}".LogInfo();
           //Remove subscription
           Twin["Group2"][propName].ChangeEvent -= appCallback2;
           Console.ReadLine();
       }
   }
}

Python

Create a Simple Console Application in Python

from agora_twin_property import Twin
from agora_logging import * 


def callback(twin:any):
    logger.info(f"callback {twin.tp_id}: {twin.key}: {twin.value}")

def callback1(twin:any):
    logger.info(f"callback 1 {twin.tp_id}: {twin.key} :{twin.value}")
    
#Subscribe to all desired properties under a GroupName
Twin.observe(callback, "Group1")
#Subscribe to a desired property under a GroupName
Twin.observe(callback1,"Group2","TwinPropName")

# Set reported property 
logger.info(f"Set property {Twin.set_reported_property("TwinPropName",30,"Group1")}")
# Get reported property
logger.info(f"Reported property: TwinPropName- {Twin.get_reported_property("TwinPropName","Group1")}")
# Get desired property
logger.info(f"Desired Property: TwinPropName- {Twin.get_desired_property("TwinPropName","Group1")}")
#Stop Observable
Twin.stop_observe("Group1")

On running the application locally, application should connect and print the below output.

TwinProperty

Redis Client

Configuration