azure - Azure IoT 中心 - 如何在设备孪生中获取更新的所需属性和报告属性？

Azure IoT 中心查询语言仅支持 SQL 语句的子集，因此以下示例（device1和双属性color）显示了缺少 CASE 语句的解决方法：

查询字符串以获取所需的属性作为 lastUpdated：

querystring = $"SELECT devices.properties.desired.color FROM devices WHERE deviceId = 'device1' and devices.properties.desired.$metadata.color.$lastUpdated > devices.properties.reported.$metadata.color.$lastUpdated";

如果返回值为空，我们必须进行第二次查询以获取报告的属性，例如：

 querystring = $"SELECT devices.properties.reported.color FROM devices WHERE deviceId = 'device1' and devices.properties.reported.$metadata.color.$lastUpdated > devices.properties.desired.$metadata.color.$lastUpdated";

如果返回值仍然为空，则设备孪生中缺少我们想要的和/或报告的属性，或者 deviceId 错误。

以下代码片段显示了上述用法的示例：

using Microsoft.Azure.Devices;
using System.Linq;
using System;
using System.Threading.Tasks;

namespace ConsoleApp3
{
    class Program
    {
        static string connectionString = "*****";

        static async Task Main(string[] args)
        {
            RegistryManager registryManager = RegistryManager.CreateFromConnectionString(connectionString);

            string deviceId = "device1";
            string propertyName = "color";
            string querystring = $"SELECT devices.properties.desired.{propertyName} FROM devices WHERE deviceId = '{deviceId}' and devices.properties.desired.$metadata.{propertyName}.$lastUpdated > devices.properties.reported.$metadata.{propertyName}.$lastUpdated";

            dynamic prop = null;
            for (int ii = 0; ii < 2; ii++)
            {
                var query = registryManager.CreateQuery(querystring);
                {
                    prop = (await query.GetNextAsJsonAsync())?.FirstOrDefault();
                    if (prop == null)
                        querystring = $"SELECT devices.properties.reported.{propertyName} FROM devices WHERE deviceId = '{deviceId}' and devices.properties.reported.$metadata.{propertyName}.$lastUpdated > devices.properties.desired.$metadata.{propertyName}.$lastUpdated";
                    else
                        break;
                }
            }
            Console.WriteLine(prop ?? $"Not found property '{propertyName}' or device '{deviceId}'");
        }
    }
}

更新：

在多个属性的情况下，我们必须通过获取的设备孪生实体中的代码单独检查每个属性。以下代码片段显示了此检查的示例：

// multiple properties
querystring = $"SELECT devices.properties FROM devices WHERE deviceId='{deviceId}'";
var query2 = registryManager.CreateQuery(querystring);
JObject prop2 = JObject.Parse((await query2.GetNextAsJsonAsync())?.FirstOrDefault());

JToken desired = prop2.SelectToken("properties.desired");
JToken reported = prop2.SelectToken("properties.reported");

string pathLastUpdated = $"$metadata.{propertyName}.$lastUpdated";          

var color = (DateTime)desired.SelectToken(pathLastUpdated) > (DateTime)reported.SelectToken(pathLastUpdated) ?
            (string)desired[propertyName] : (string)reported[propertyName];

// more properties

Console.WriteLine(color);

另外，您可以创建一个扩展类来简化代码，请参见以下示例：

public static class JObjectExtensions
{
    public static T GetLastUpdated<T>(this JObject properties, string propertyName)
    {
        JToken desired = properties.SelectToken("properties.desired");
        JToken reported = properties.SelectToken("properties.reported");
        string pathLastUpdated = $"$metadata.{propertyName}.$lastUpdated";

        return (DateTime)desired.SelectToken(pathLastUpdated) > (DateTime)reported.SelectToken(pathLastUpdated) ?
            desired.SelectToken(propertyName).ToObject<T>() : reported.SelectToken(propertyName).ToObject<T>();
    }

    public static string GetLastUpdated(this JObject properties, string propertyName)
    {
        return GetLastUpdated<string>(properties, propertyName);
    }
}

上述扩展的以下用法显示了如何根据 lastUpdated 时间戳获得任何所需的与报告的属性：

color = prop2.GetLastUpdated(propertyName);

string color2 = prop2.GetLastUpdated("test.color");

var test = prop2.GetLastUpdated<JObject>("test");

string jsontext = prop2.GetLastUpdated<JObject>("test").ToString(Formatting.None);

var test2 = prop2.GetLastUpdated<Test>("test");

int counter = prop2.GetLastUpdated<int>("counter");

请注意，在缺少属性的情况下会引发异常。

azure - Azure IoT 中心 - 如何在设备孪生中获取更新的所需属性和报告属性？

问题描述

解决方案

推荐阅读