Tutorial: Create an Azure Digital Twins graph using a sample client app

In this tutorial, you'll build a graph in Azure Digital Twins using models, twins, and relationships. The tool for this tutorial is the sample command-line client application for interacting with an Azure Digital Twins instance. The client app is similar to the one written in Code a client app.

You can use this sample to perform essential Azure Digital Twins actions such as uploading models, creating and modifying twins, and creating relationships. You can also look at the code of the sample to learn about the Azure Digital Twins APIs, and practice implementing your own commands by modifying the sample project however you want.

In this tutorial, you will...

Prerequisites

To complete the steps in this tutorial, you'll need to first complete the following prerequisites.

If you don't have an Azure subscription, create a free account before you begin.

Get required resources

To complete this tutorial, install Visual Studio 2019, version 16.5 or later on your development machine. If you have an older version installed already, you can open the Visual Studio Installer app on your machine and follow the prompts to update your installation.

The tutorial is driven by an Azure Digital Twins end-to-end sample project written in C#. Get the sample project on your machine by navigating to the sample link, and selecting the Browse code button underneath the title. This will take you to the GitHub repo for the samples, which you can download as a .zip by selecting the Code button followed by Download ZIP.

This will download a .zip folder to your machine as digital-twins-samples-master.zip. Unzip the folder and extract the files.

Prepare an Azure Digital Twins instance

To work with Azure Digital Twins in this article, you first need to set up an Azure Digital Twins instance. You also need the required permissions for using it. If you already have an Azure Digital Twins instance set up, you can use it instead.

Otherwise, follow the instructions in Set up an instance and authentication. The instructions contain information to help you verify that you've completed each step successfully.

After you set up your instance, make a note of the following values. You'll need these values to connect to the instance later:

• The instance's host name. You can find the host name in the Azure portal.
• The Azure subscription that you used to create the instance. Either its name or its ID will work. You can find the subscription on your instance's Overview page in the Azure portal.

Configure the sample project

Next, set up a sample client application that will interact with your Azure Digital Twins instance.

Navigate on your machine to the file you downloaded earlier from Azure Digital Twins end-to-end samples (and unzip it if you haven't already).

Once inside the folder, navigate into AdtSampleApp. Open AdtE2ESample.sln in Visual Studio 2019.

In Visual Studio, select the SampleClientApp > appsettings.json file to open it in the editing window. This will serve as a pre-set JSON file with the necessary configuration variables to run the project.

In the file body, change the instanceUrl to your Azure Digital Twins instance host name URL (by adding https:// in front of the host name, as shown below).

{
  "instanceUrl": "https://<your-Azure-Digital-Twins-instance-host-name>"
}

Save and close the file.

Next, configure the appsettings.json file to be copied to the output directory when you build the SampleClientApp. To do this, right-select the appsettings.json file, and choose Properties. In the Properties inspector, look for the Copy to Output Directory property. Change the value to Copy if newer if it is not set to that already.

Keep the AdtE2ESample project open in Visual Studio to continue using it in the tutorial.

Set up local Azure credentials

This sample uses DefaultAzureCredential (part of the Azure.Identity library) to authenticate users with the Azure Digital Twins instance when you run it on your local machine. For more information on different ways a client app can authenticate with Azure Digital Twins, see Write app authentication code.

With DefaultAzureCredential, the sample will search for credentials in your local environment, like an Azure sign-in in a local Azure CLI or in Visual Studio or Visual Studio Code. For this reason, you should sign in to Azure locally through one of these mechanisms to set up credentials for the sample.

If you're using Visual Studio or Visual Studio Code to run the code sample, make sure you're signed in to that editor with the same Azure credentials that you want to use to access your Azure Digital Twins instance.

Otherwise, you can install the local Azure CLI, start a command prompt on your machine, and run the az login command to sign in to your Azure account. After you sign in, when you run your code sample, it should log you in automatically.

Run the sample project

Now that the app and authentication are set up, run the project with this button in the toolbar:

A console window will open, carry out authentication, and wait for a command.

Here's a screenshot of what the project console looks like:

Once you've confirmed the app is running successfully, close the console window to stop running the app for now. You'll run it again later in the article.

Model a physical environment with DTDL

Now that the Azure Digital Twins instance and sample app are set up, you can begin building a graph of a scenario.

The first step in creating an Azure Digital Twins solution is defining twin models for your environment.

Models are similar to classes in object-oriented programming languages; they provide user-defined templates for digital twins to follow and instantiate later. They're written in a JSON-like language called Digital Twins Definition Language (DTDL), and can define a twin's properties, telemetry, relationships, and components.

In your Visual Studio window where the AdtE2ESample project is open, use the Solution Explorer pane to navigate to the AdtSampleApp\SampleClientApp\Models folder. This folder contains sample models.

Select Room.json to open it in the editing window, and change it in the following ways:

1. Update the version number, to indicate that you are providing a more-updated version of this model. Do this by changing the 1 at the end of the @id value to a 2. Any number greater than the current version number will also work.

2. Edit a property. Change the name of the Humidity property to HumidityLevel (or something different if you want. If you use something different than HumidityLevel, remember what you used and continue using that instead of HumidityLevel throughout the tutorial).

3. Add a property. Underneath the HumidityLevel property that ends on line 15, paste the following code to add a RoomName property to the room:

   ,{
     "@type": "Property",
     "name": "RoomName",
     "schema": "string"
   }
   

4. Add a relationship. Underneath the RoomName property that you just added, paste the following code to add the ability for this type of twin to form contains relationships with other twins:

   ,{
     "@type": "Relationship",
     "name": "contains"
   }
   

When you are finished, the updated model should match this:

{
    "@id": "dtmi:example:Room;2",
    "@type": "Interface",
    "displayName": "Room",
    "contents": [
      {
        "@type": "Property",
        "name": "Temperature",
        "schema": "double"
      },
      {
        "@type": "Property",
        "name": "HumidityLevel",
        "schema": "double"
      }
      ,{
        "@type": "Property",
        "name": "RoomName",
        "schema": "string"
      }
      ,{
        "@type": "Relationship",
        "name": "contains"
      }
    ],
    "@context": "dtmi:dtdl:context;2"
  }

Make sure to save the file before moving on.

Upload models to Azure Digital Twins

After designing models, you need to upload them to your Azure Digital Twins instance. Doing so configures your Azure Digital Twins service instance with your own custom domain vocabulary. Once you've uploaded the models, you can create twin instances that use them.

1. After editing the Room.json file in the previous section, start running the console app again.

2. In the project console window, run the following command to upload your updated Room model along with a Floor model that you'll also use in the next section to create different types of twins.

   CreateModels Room Floor
   

   The output should indicate the models were created successfully.

3. Verify the models were created by running the command GetModels true. This command will print the full information for all the models that have been uploaded to your Azure Digital Twins instance. Look for the edited Room model in the results:

   

Errors

The sample application also handles errors from the service.

Rerun the CreateModels command to try re-uploading one of the same models you uploaded, for a second time:

CreateModels Room

As models cannot be overwritten, this command will now return a service error. For the details on how to delete existing models, see Manage DTDL models.

Response 409: Service request failed.
Status: 409 (Conflict)

Content:
{"error":{"code":"ModelAlreadyExists","message":"Could not add model dtmi:example:Room;2 as it already exists. Use Model_List API to view models that already exist. See the Swagger example.(http://aka.ms/ModelListSwSmpl)"}}

Headers:
Strict-Transport-Security: REDACTED
Date: Wed, 20 May 2020 00:53:49 GMT
Content-Length: 223
Content-Type: application/json; charset=utf-8

Create digital twins

Now that some models have been uploaded to your Azure Digital Twins instance, you can create digital twins based on the model definitions. Digital twins represent the entities within your business environment—things like sensors on a farm, rooms in a building, or lights in a car.

To create a digital twin, you use the CreateDigitalTwin command. You must reference the model that the twin is based on, and can optionally define initial values for any properties in the model. You don't have to pass any relationship information at this stage.

1. Run this code in the running project console to create several twins, based on the Room model you updated earlier and another model, Floor. Recall that Room has three properties, so you can provide arguments with the initial values for these properties. (Initializing property values is optional in general, but they're needed for this tutorial.)

   CreateDigitalTwin dtmi:example:Room;2 room0 RoomName string Room0 Temperature double 70 HumidityLevel double 30
   CreateDigitalTwin dtmi:example:Room;2 room1 RoomName string Room1 Temperature double 80 HumidityLevel double 60
   CreateDigitalTwin dtmi:example:Floor;1 floor0
   CreateDigitalTwin dtmi:example:Floor;1 floor1
   

   The output from these commands should indicate the twins were created successfully.

   

2. You can verify that the twins were created by running the Query command. This command queries your Azure Digital Twins instance for all the digital twins it contains. Look for the room0, room1, floor0, and floor1 twins in the results.

Modify a digital twin

You can also modify the properties of a twin you've created.

1. Run this command to change room0's RoomName from "Room0" to "PresidentialSuite":

   UpdateDigitalTwin room0 add /RoomName string PresidentialSuite
   

   The output should indicate the twin was updated successfully.

2. You can verify the update succeeded by running this command to see room0's information:

   GetDigitalTwin room0
   

   The output should reflect the updated name.

Create a graph by adding relationships

Next, you can create some relationships between these twins, to connect them into a twin graph. Twin graphs are used to represent an entire environment.

The types of relationships that you can create from one twin to another are defined within the models that you uploaded earlier. The model definition for Floor specifies that floors can have a type of relationship called contains, which makes it possible to create a contains-type relationship from each Floor twin to the corresponding room that it contains.

To add a relationship, use the CreateRelationship command. Specify the twin that the relationship is coming from, the type of relationship, and the twin that the relationship is connecting to. Lastly, give the relationship a unique ID.

1. Run the following code to add a "contains" relationship from each of the Floor twins you created earlier to a corresponding Room twin. The relationships are named relationship0 and relationship1.

   CreateRelationship floor0 contains room0 relationship0
   CreateRelationship floor1 contains room1 relationship1
   

   Tip

   The contains relationship in the Floor model was also defined with two string properties, ownershipUser and ownershipDepartment, so you can also provide arguments with the initial values for these when you create the relationships. Here's an alternate version of the command above to create relationship0 that also specifies initial values for these properties:

   CreateRelationship floor0 contains room0 relationship0 ownershipUser string MyUser ownershipDepartment string myDepartment
   

   The output from these commands confirms that the relationships were created successfully:

   

2. You can verify the relationships with any of the following commands, which will print the relationships in your Azure Digital Twins instance.

   • To see all relationships coming off of each floor (viewing the relationships from one side):

     GetRelationships floor0
     GetRelationships floor1
     

   • To see all relationships arriving at each room (viewing the relationship from the "other" side):

     GetIncomingRelationships room0
     GetIncomingRelationships room1
     

   • To look for these relationships individually, by ID:

     GetRelationship floor0 relationship0
     GetRelationship floor1 relationship1
     

The twins and relationships you have set up in this tutorial form the following conceptual graph:

Query the twin graph to answer environment questions

A main feature of Azure Digital Twins is the ability to query your twin graph easily and efficiently to answer questions about your environment.

Run the following commands in the running project console to answer some questions about the sample environment.

1. What are all the entities from my environment represented in Azure Digital Twins? (query all)

   Query
   

   This command allows you to take stock of your environment at a glance, and make sure everything is represented as you want it to be within Azure Digital Twins. The result of this command is an output containing each digital twin with its details. Here's an excerpt:

   

   Tip

   In the sample project, the command Query without any additional arguments is the equivalent of Query SELECT * FROM DIGITALTWINS. To query all the twins in your instance using the Query APIs or the CLI commands, use the longer (complete) query.

2. What are all the rooms in my environment? (query by model)

   Query SELECT * FROM DIGITALTWINS T WHERE IS_OF_MODEL(T, 'dtmi:example:Room;2')
   

   You can restrict your query to twins of a certain type, to get more specific information about what's represented. The result of this shows room0 and room1, but does not show floor0 or floor1 (since they're floors, not rooms).

   

3. What are all the rooms on floor0? (query by relationship)

   Query SELECT room FROM DIGITALTWINS floor JOIN room RELATED floor.contains where floor.$dtId = 'floor0'
   

   You can query based on relationships in your graph, to get information about how twins are connected or to restrict your query to a certain area. Only room0 is on floor0, so it's the only room in the result.

   

4. What are all the twins in my environment with a temperature above 75? (query by property)

   Query SELECT * FROM DigitalTwins T WHERE T.Temperature > 75
   

   You can query the graph based on properties to answer various questions, including finding outliers in your environment that might need attention. Other comparison operators (<,>, =, or !=) are also supported. room1 shows up in the results here, because it has a temperature of 80.

   

5. What are all the rooms on floor0 with a temperature above 75? (compound query)

   Query SELECT room FROM DIGITALTWINS floor JOIN room RELATED floor.contains where floor.$dtId = 'floor0' AND IS_OF_MODEL(room, 'dtmi:example:Room;2') AND room.Temperature > 75
   

   You can also combine the earlier queries like you would in SQL, using combination operators such as AND, OR, NOT. This query uses AND to make the previous query about twin temperatures more specific. The result now only includes rooms with temperatures above 75 that are on floor0—which in this case, is none of them. The result set is empty.

   

Clean up resources

After completing this tutorial, you can choose which resources you want to remove, depending on what you want to do next.

• If you plan to continue to the next tutorial, you can keep the resources you set up here to continue using this Azure Digital Twins instance and configured sample app for the next tutorial

• If you want to continue using the Azure Digital Twins instance, but clear out all of its models, twins, and relationships, you can use the sample app's DeleteAllTwins and DeleteAllModels commands to clear the twins and models in your instance, respectively.

• If you do not need any of the resources you created in this tutorial, you can delete the Azure Digital Twins instance and all other resources from this article with the az group delete command. This deletes all Azure resources in a resource group, as well as the resource group itself.

  Important

  Deleting a resource group is irreversible. The resource group and all the resources contained in it are permanently deleted. Make sure that you don't accidentally delete the wrong resource group or resources.

  Open Azure Cloud Shell, and run the following command to delete the resource group and everything it contains.

  az group delete --name <your-resource-group>
  

You may also want to delete the project folder from your local machine.

Next steps

In this tutorial, you got started with Azure Digital Twins by building a graph in your instance using a sample client application. You created models, digital twins, and relationships to form a graph. You also ran some queries on the graph, to get an idea of what kinds of questions Azure Digital Twins can answer about an environment.

Continue to the next tutorial to combine Azure Digital Twins with other Azure services to complete a data-driven, end-to-end scenario: