How To Notify Clients of Cosmos DB Changes with Azure SignalR and Azure Functions

This is the fourth part in a series of articles.

The Cosmos DB Azure Functions trigger can be used in conjunction with the Azure SignalR Service to create real-time notifications of changes made to data in Cosmos DB, all in a serverless way.

Azure Cosmos DB Change Notifications with Azure Functions and SignalR

If you want to learn more about how to setup the SignalR Service, check out this previous article.

In this series we’ve been using the domain of pizza delivery. In this article we’ll see how  updates in Cosmos DB can trigger a notification on an HTML client – you may have seen this if you’ve ordered pizza online where the delivery driver is tracked by GPS on a map.

The first thing to do is set up an Azure SignalR Service in Azure and add the SignalR Service connection string in the local.settings.json file which was covered in this article.

We can now add the negotiate function:

[FunctionName("negotiate")]
public static SignalRConnectionInfo GetDriverLocationUpdatesSignalRInfo(
    [HttpTrigger(AuthorizationLevel.Anonymous, "post")] HttpRequest req,
    [SignalRConnectionInfo(HubName = "driverlocationnotifications")] SignalRConnectionInfo connectionInfo)
{
    return connectionInfo;
}

The preceding code sets the SignalR hub to be used in this example as “driverlocationnotifications”, we’ll use the same hub name in the function that actually sends updates to clients.

The next thing to do is add a function that is triggered when changes are made to the location of pizza delivery drivers (note the trigger will also fire for new documents that are added):

[FunctionName("PizzaDriverLocationUpdated")]
public static async Task Run([CosmosDBTrigger(
    databaseName: "pizza",
    collectionName: "driver",
    ConnectionStringSetting = "pizzaConnection")] IReadOnlyList<Document> modifiedDrivers,
    [SignalR(HubName = "driverlocationnotifications")] IAsyncCollector<SignalRMessage> signalRMessages,
    ILogger log)
{
    if (modifiedDrivers != null)
    {
        log.LogInformation($"Total modified drivers: {modifiedDrivers.Count}");

        foreach (var modifiedDriver in modifiedDrivers)
        {
            var driverName = modifiedDriver.GetPropertyValue<string>("Name");
            var driverLat = modifiedDriver.GetPropertyValue<double>("Latitude");
            var driverLong = modifiedDriver.GetPropertyValue<double>("Longitude");

            log.LogInformation($"Driver {modifiedDriver.Id} {driverName} was updated (lat,long) {driverLat}, {driverLong}");

            var message = new DriverLocationUpdatedMessage
            {
                DriverId = modifiedDriver.Id,
                DriverName = driverName,
                Latitude = driverLat,
                Longitude = driverLong
            };

            await signalRMessages.AddAsync(new SignalRMessage
            {
                Target = "driverLocationUpdated",
                Arguments = new[] { message }
            });
        }
    }
}

The preceding code uses the [CosmosDBTrigger] to fire the function when there are changes made to the “driver” collection in the “pizza” database.

The [SignalR] binding attribute allows outgoing SignalR messages to be sent to connected clients by adding messages to the IAsyncCollector<SignalRMessage> signalRMessages object. Notice that the type of the Cosmos DB trigger is IReadOnlyList<Document>, to get the actual data items of the document we use the GetPropertyValue method, for example to get the driver name: modifiedDriver.GetPropertyValue<string>("Name").

In the HTML, we can connect to the “driverlocationnotifications” SignalR hub, and then get notifications when any driver location changes, in reality we would probably only want to get messages for the driver that is delivering our pizza but for simplicity we won’t worry about it in this demo code.

The following is the HTML to make this work:

<html>

<head>
     <!--Adapted from: https://azure-samples.github.io/signalr-service-quickstart-serverless-chat/demo/chat-v2/ -->

    <title>SignalR Demo</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.1.3/dist/css/bootstrap.min.css">

    <style>
        .slide-fade-enter-active, .slide-fade-leave-active {
            transition: all 1s ease;
        }

        .slide-fade-enter, .slide-fade-leave-to {
            height: 0px;
            overflow-y: hidden;
            opacity: 0;
        }
    </style>
</head>

<body>
    <p>&nbsp;</p>
    <div id="app" class="container">
        <h3>Your Pizza Is On Its Way!!</h3>

        <div class="row" v-if="!ready">
            <div class="col-sm">
                <div>Loading...</div>
            </div>
        </div>
        <div v-if="ready">
            <transition-group name="slide-fade" tag="div">
                <div class="row" v-for="driver in drivers" v-bind:key="driver.DriverId">
                    <div class="col-sm">
                        <hr />
                        <div>
                            <div style="display: inline-block; padding-left: 12px;">
                                <div>
                                    <span class="text-info small"><strong>{{ driver.DriverName }}</strong> just changed location:</span>
                                </div>
                                <div>
                                    {{driver.Latitude}},{{driver.Longitude}}
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </transition-group>
        </div>
    </div>

    <script src="https://cdn.jsdelivr.net/npm/vue@2.5.17/dist/vue.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/@aspnet/signalr@1.1.2/dist/browser/signalr.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/axios@0.18.0/dist/axios.min.js"></script>

    <script>
        const data = {
          drivers: [],
          ready: false
        };

        const app = new Vue({
          el: '#app',
          data: data,
          methods: {
          }
        });

        const connection = new signalR.HubConnectionBuilder()
          .withUrl('http://localhost:7071/api')
          .configureLogging(signalR.LogLevel.Information)
          .build();

        connection.on('driverLocationUpdated', driverLocationUpdated);
        connection.onclose(() => console.log('disconnected'));

        console.log('connecting...');
        connection.start()
            .then(() => data.ready = true)
            .catch(console.error);

        let counter = 0;

        function driverLocationUpdated(driverLocationUpdatedMessage) {
        driverLocationUpdatedMessage.id = counter++; // vue transitions need an id
        data.drivers.unshift(driverLocationUpdatedMessage);
    }
    </script>
</body>

</html>

Now when changes are made to the documents in the driver collection, the Azure Function will execute and send out Azure SignalR Service messages to clients. In this example we’re just writing out the messages in the page, but you can image the latitude and longitude being used to draw a little car image on top of a map, etc.

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Writing Azure Cosmos DB Data from Azure Functions

This is the third part in a series of articles.

In part 2 of this series we saw how to read data from Cosmos DB, in this article we’ll see how to write data to Cosmos DB from an Azure Function.

As with input, output is achieved by the use of the [CosmosDB] binding attribute and as before, the database name, collection name, id, partition, and connection string can be defined.

In part 2 we saw how to use binding expressions to take data from the HTTP querystring and use that to select a document to read in (e.g. by Id). In this article we’ll see how we can do a similar thing when the trigger type is for a storage queue.

The following function is triggered when a message is written to the “update-pizza-driver-location” queue:

[FunctionName("UpdatePizzaDriverLocation")]
[return: CosmosDB(databaseName: "pizza", collectionName: "driver", ConnectionStringSetting = "pizzaConnection", Id = "{Id}", PartitionKey = "{StoreId}")]
public static Driver Run(
    [QueueTrigger("update-pizza-driver-location")] PizzaDriverLocationUpdate locationUpdate,
    [CosmosDB(databaseName: "pizza", collectionName: "driver", ConnectionStringSetting = "pizzaConnection", Id = "{Id}", PartitionKey = "{StoreId}")] Driver driver,            
    ILogger log)
{
    if (driver is null)
    {
        log.LogError($"Driver Id/partition {locationUpdate.Id}/{locationUpdate.StoreId} not found in database.");
        return null;
    }

    driver.Latitude = locationUpdate.NewLat;
    driver.Longitude = locationUpdate.NewLong;

    return driver;
}

The first thing to notice in the preceding function that there are 2 instances of the [CosmosDB] binding attribute, one as the return binding for the method (the output binding to perform the update) and the input binding in the Run method parameter (the input binding to read the current state of the Driver).

Another thing to notice is the use of the {Id} and {StoreId} binding expressions. These expressions assume that the incoming queue message contains JSON properties that match these expressions, for example:

{
    "Id" : "1",
    "StoreId" : "101",
    "NewLat" : 111.2,
    "NewLong" : 3110.3
}

The Driver and PizzaDriverLocationUpdate classes look like the following:

public class PizzaDriverLocationUpdate
{
    public string Id { get; set; }
    public string StoreId { get; set; }
    public double NewLat { get; set; }
    public double NewLong { get; set; }
}

 

public class Driver
{
    [JsonProperty(PropertyName = "id")]
    public string Id { get; set; }
    public string StoreId { get; set; }
    public string Name { get; set; }
    public double Latitude { get; set; }
    public double Longitude { get; set; }
}

Note in the Driver class, the [JsonProperty(PropertyName = "id")] attribute is mapping Id to id in Cosmos DB.

If you want to write multiple documents from a single function invocation you make use of an IAsyncCollector, for example IAsyncCollector<Driver> drivers and then use drivers.AddAsync(newDriver) method to write multiple documents.

In the next part of this series we’ll see how we can combine Azure Cosmos DB triggers with SignalR to create notifications to clients when data changes.

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Reading Azure Cosmos DB Data In Azure Functions

This is the second part in a series of articles.

In addition to triggering a function when Cosmos DB data changes (as we saw in part one) you can also read data in from Cosmos DB when a function executes. The simplest way to do this is to use an input binding.

The [CosmosDB] binding attribute can be used both as an input binding and an output binding. When used as an input binding it allows one or more documents to be retrieved from the database.

When using the attribute there are a number of ways to configure it including:

  • The Cosmos DB database name
  • The collection name
  • The document Id to retrieve
  • The partition key
  • And the connection string app setting

Reading a Single Cosmos DB Document in an Azure Function

The following code shows an Azure Function that is triggered from an HTTP GET request:

[FunctionName("GetDriver")]
public static async Task<IActionResult> Run(
    [HttpTrigger(AuthorizationLevel.Function, "get", Route = null)] HttpRequest req,
    [CosmosDB(databaseName: "pizza",collectionName: "driver", Id = "{Query.id}", PartitionKey = "{Query.storeId}", ConnectionStringSetting = "pizzaConnection")] Driver driver,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    if (driver is null)
    {
        return new NotFoundResult();
    }

    return new OkObjectResult(driver);
}

Notice first the [CosmosDB] binding attribute. The combination of the Id and PartitionKey will determine the Driver object (if any) that will be retrieved. Note the format of these two: {Query.id} and {Query.storeId}.This will look for query string parameters in the incoming HTTP GET called id and storeId, for example: http://localhost:7071/api/GetDriver?id=1&storeId=101

If no document is found, driver will be null.

If the document was found it will be returned as JSON to the caller.

Reading Multiple Cosmos DB Documents in an Azure Function Using SqlQuery

The following function will get the latest 100 drivers (as sorted by the built in timestamp _ts property):

[FunctionName("GetDrivers")]
public static async Task<IActionResult> GetDrivers(
    [HttpTrigger(AuthorizationLevel.Function, "get", Route = null)] HttpRequest req,
    [CosmosDB(databaseName: "pizza", collectionName: "driver", SqlQuery = "SELECT top 100 * FROM driver order by driver._ts desc", ConnectionStringSetting = "pizzaConnection")] IEnumerable<Driver> drivers,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    if (drivers is null)
    {
        return new NotFoundResult();
    }

    foreach (var driver in drivers)
    {
        log.LogInformation(driver.Name);
    }

    return new OkObjectResult(drivers);
}

There’s a couple of things to notice in the preceding code. The first is that instead of a single Driver, the binding now returns IEnumerable<Driver> drivers. Also notice that the binding no longer has Id and PartitionKey.

Reading Multiple Cosmos DB Documents Based on Query String Parameter

A more advanced technique is to bind to an instance of DocumentClient. This allows more fine grained/low level/more specific access of data, such as using a LINQ query to perform the search:

[FunctionName("GetDriversForStore")]
public static async Task<IActionResult> GetDriversForStore(
    [HttpTrigger(AuthorizationLevel.Function, "get", Route = null)] HttpRequest req,
    [CosmosDB( ConnectionStringSetting = "pizzaConnection")] DocumentClient client,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");
    
    // Validation and error checking omitted for demo purposes
               
    string storeId = req.Query["storeId"]; // read storeId to get driver for from querystring

    Uri driverCollectionUri = UriFactory.CreateDocumentCollectionUri(databaseId: "pizza", collectionId: "driver");

    var options = new FeedOptions { EnableCrossPartitionQuery = true }; // Enable cross partition query

    IDocumentQuery<Driver> query = client.CreateDocumentQuery<Driver>(driverCollectionUri, options)
                                         .Where(driver => driver.StoreId == storeId)
                                         .AsDocumentQuery();

    var driversForStore = new List<Driver>();

    while (query.HasMoreResults)
    {
        foreach (Driver driver in await query.ExecuteNextAsync())
        {
            driversForStore.Add(driver);
        }
    }                       

    return new OkObjectResult(driversForStore);
}

The preceding code returns all drivers that belong to a specific store passed in as a querystring storeId parameter.

In the next part of this series we’ll see how to write data out to Cosmos DB when a function executes.

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Getting Started with Azure Cosmos DB and Azure Functions

This is the first part in a series of articles.

Azure Cosmos DB is a “globally distributed, multi-model database service. With a click of a button, Cosmos DB enables you to elastically and independently scale throughput and storage across any number of Azure regions worldwide. You can elastically scale throughput and storage, and take advantage of fast, single-digit-millisecond data access using your favorite API including SQL, MongoDB, Cassandra, Tables, or Gremlin” [Microsoft]

One way to respond to changes in Cosmos is to use Azure Functions. When changes occur (currently limited to inserts and updates, e.g. not deletions ) the Function can be notified and executes.

Azure Function Cosmos DB triggers under the hood make use of the Azure Cosmos DB change feed to know when to execute functions.

Installing the Azure Cosmos Emulator

You can use the Azure Cosmos Emulator to get started locally without even needing an Azure subscription.

Once the emulator is downloaded and installed on your development PC (a Docker version is also available) you can start the  emulator from the start menu.

When running you can see the icon in the Windows taskbar notification area and it will pop up a browser window pointing to https://localhost:8081/_explorer/index.html as the following screenshot shows:

Azure Cosmos Emulator portal

Notice in the preceding screenshot the Primary Connection String, you will need to copy this for use in the local app settings later.

Creating an Azure Function Triggered from Cosmos DB

Once you have created an Azure Function project in Visual Studio, you need to add the Microsoft.Azure.WebJobs.Extensions.CosmosDB NuGet package to get access to the .NET C# bindings.

Now the package is installed (and with an up to date installation of Visual Studio) you can right click the Azure Functions project and choose Add –> New Azure Function…

Give the function a name and for the trigger type choose Cosmos - this will create a boiler plate function like the following:

public static class PizzaDriverLocationUpdated
{
    [FunctionName("PizzaDriverLocationUpdated")]
    public static void Run([CosmosDBTrigger(
        databaseName: "databaseName",
        collectionName: "collectionName",
        ConnectionStringSetting = "",
        LeaseCollectionName = "leases")]IReadOnlyList<Document> input, ILogger log)
    {
        if (input != null && input.Count > 0)
        {
            log.LogInformation("Documents modified " + input.Count);
            log.LogInformation("First document Id " + input[0].Id);
        }
    }
}

The preceding code uses the [CosmosDBTrigger] attribute to tell this function to execute when there are changes as specified by the following attribute parameters/properties:

  • databaseName - Azure Cosmos DB database with the monitored collection
  • collectionName – Collection being monitored for changes
  • ConnectionStringSetting – App setting name containing the connection string to the Azure Cosmos DB being monitored
  • LeaseCollectionName - name of the collection used to store leases, defaults to “leases” if not specified

The LeaseCollectionName is required by the trigger to store leases over Cosmos DB partitions, one thing to note: “If multiple functions are configured to use a Cosmos DB trigger for the same collection, each of the functions should use a dedicated lease collection or specify a different LeaseCollectionPrefix for each function. Otherwise, only one of the functions will be triggered” [Microsoft]

How to Create a Database and Collection in the Azure Cosmos Emulator

In the emulator portal in the browser, click Explorer.This will allow you to create collections in the emulator.

Click the New Collection button and enter the following:

  • Database id: pizza
  • Collection Id: driverLocation
  • Partition key: /storeId

Creating a new collection in the Azure Cosmos DB Emulator

Save this new collection.

Configuring an Azure Function Cosmos DB Trigger

Modify the function that was created earlier to be as follows:

public static class PizzaDriverLocationUpdated
{
    [FunctionName("PizzaDriverLocationUpdated")]
    public static void Run([CosmosDBTrigger(
        databaseName: "pizza",
        collectionName: "driverLocation",
        ConnectionStringSetting = "pizzaConnection")] IReadOnlyList<Document> input,
        ILogger log)
    {
        if (input != null && input.Count > 0)
        {
            log.LogInformation("Documents modified " + input.Count);
            log.LogInformation("First document Id " + input[0].Id);
        }
    }
}

Notice in the preceding code that the databaseName and collectionName settings match what we just created in the emulator.

The ConnectionStringSetting is set to “pizzaConnection” – this needs to be in the function settings, in the case of local development in the local.settings.json file:

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet",
    "pizzaConnection": "AccountEndpoint=https://localhost:8081/;AccountKey=C2y6yDjf5/R+ob0N8A7Cgv30VRDJIWEHLM+4QDU5DE2nQ9nDuVTqobD4b8mGGyPMbIZnqyMsEcaGQy67XIw/Jw=="
  },
  "Host": {
    "LocalHttpPort": 7071,
    "CORS": "http://localhost:3872",
    "CORSCredentials": true
  }
}

Notice in the preceding settings, the value for the pizzaConnection item is the Primary Connection String copied from the Azure Cosmos Emulator.

Testing the Function Locally

Now that the function code is configured and the database and collection exist in the emulator, hit F5 in Visual Studio (or click Run) and the local functions runtime will start.

Once the runtime has started, head back to the Cosmos Emulator in the browser, click on Pizza –> driverLocation –> Documents and click the New Document button.

Creating a new document in the Cosmos DB emulator

Add the following:

{
    "id": "1",
    "storeId": 42,
    "name": "Sarah",
    "lat" : 52,
    "long": 2
}

And click Save.

Head back to the locally running functions runtime window and you will see the function has noticed this new document and executed:

Executing 'PizzaDriverLocationUpdated' (Reason='New changes on collection driverLocation at 2019-05-10T04:10:29.9913171Z', Id=203ae791-c7d4-4270-ac6b-501f313c3805)
Documents modified 1
First document Id 1
Executed 'PizzaDriverLocationUpdated' (Succeeded, Id=203ae791-c7d4-4270-ac6b-501f313c3805)

If you head back to the emulator, modify the document (e.g. change the name to “Amrit”) and click Update, the function will trigger a second time:

Executing 'PizzaDriverLocationUpdated' (Reason='New changes on collection driverLocation at 2019-05-10T04:13:00.8233214Z', Id=778caddd-9f19-42fa-9d9d-6c5dd5892a25)
Documents modified 1
First document Id 1
Executed 'PizzaDriverLocationUpdated' (Succeeded, Id=778caddd-9f19-42fa-9d9d-6c5dd5892a25)

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Diagnosing Failing Tests More Easily and Improving Test Code Readability

Sometimes the assertions that come bundled with a testing framework are suboptimal in that they do not provide test failure messages that allow easier understanding of why/where the test failed.

If the test failure message does not provide enough information, it may be necessary to run the test in debug mode just to find out what went wrong before fixing it. This test debugging step is wasted time.

Using the built-in assertions can also be suboptimal from a code readability point of view, though this can be a matter of personal preference.

The Fluent Assertions library aims to solve these two problems by:

  • Providing better, more descriptive test failure messages; and
  • Providing a more fluent, readable  syntax for assertions

Let’s take a look at some examples. Note that Fluent Assertions is an “add on” to whatever testing framework you are using (NUnit, xUnit.net, etc.).

The following test (using NUnit) shows a simple case:

public class CreditCardApplication
{
    public string Name { get; set; }
    public int Age { get; set; }
    public decimal AnnualGrossIncome { get; set; }

    public int CalculateCreditScore()
    {
        int score = 0;

        if (Age > 30)
        {
            score += 10;
        }

        if (AnnualGrossIncome < 50_000)
        {
            score += 30;
        }
        else
        {
            score += 30;
        }

        return score;
    }
}

 

[Test]
public void NUnitExample()
{
    var application = new CreditCardApplication
    {
        Name = "Sarah",
        Age = 31,
        AnnualGrossIncome = 50_001
    };

    Assert.That(application.CalculateCreditScore(), Is.EqualTo(50));
}

When this test fails using the built-in NUnit asserts, the failure message is:

Test Outcome:    Failed

Result Message:    
Expected: 50
  But was:  40

Notice in the preceding test failure message we don’t have any context about what is failing or what the number 50 and 40 represent. While well-named tests can help with this, it can be helpful to have additional information, especially when there are multiple asserts in a single test method.

The same test in xUnit.net:

[Fact]
public void XUnitExample()
{
    var application = new CreditCardApplication
    {
        Name = "Sarah",
        Age = 31,
        AnnualGrossIncome = 50_001
    };

    Assert.Equal(50, application.CalculateCreditScore());
}

Produces the message:

Test Outcome:    Failed

Result Message:    
Assert.Equal() Failure
Expected: 50
Actual:   40

Once again there is no additional context about the failure.

The same test written using Fluent Assertions would look like the following:

[Fact]
public void XUnitExample_WithFluentAssertions()
{
    var application = new CreditCardApplication
    {
        Name = "Sarah",
        Age = 31,
        AnnualGrossIncome = 50_001
    };


    application.CalculateCreditScore().Should().Be(50);
}

Now when the test fails, the message looks like the following:

Test Outcome:    Failed
Result Message:
Expected application.CalculateCreditScore() to be 50, but found 40.

Notice the failure is telling us the method (or variable) name that is being asserted on – in this example the CalculateCreditScore method.

Optionally you can also add a “because” to further clarify failures:

[Fact]
public void XUnitExample_WithFluentAssertions_Because()
{
    var application = new CreditCardApplication
    {
        Name = "Sarah",
        Age = 31,
        AnnualGrossIncome = 50_001
    };


    application.CalculateCreditScore().Should().Be(50, because: "an age of {0} should be worth 20 points and an income of {1} should be worth 30 points.", application.Age, application.AnnualGrossIncome);
}

This would now produce the following failure message:

Test Outcome:    Failed
Result Message:    
Expected application.CalculateCreditScore() to be 50 because an age of 31 should be worth 20 points and an income of 50001 should be worth 30 points., but found 40.

Notice the “because” not only gives a richer failure message but also helps describe the test. While you probably wouldn’t use the because feature on every assert, you could use it to clarify tests that may not be obvious at first sight or that represent complex domain logic or algorithms. You should also be aware that the because text may need modifying if the business logic changes and this may introduce an additional maintenance cost.

If you want to learn more about Fluent Assertions, check out my express Pluralsight course Improving Unit Tests with Fluent Assertions which you can get access to with a Pluralsight free trial by clicking the banner below.

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Returning HTTP Status Codes from Azure Functions

(This post refers to Azure Functions v2)

When creating HTTP-triggered Azure Functions there are a number of ways to indicate results back to the calling client.

Returning HTTP Status Codes Manually

To return a specific status code to the client you can create an instance of one of the …Result classes and return that from the function body.

The following example returns an instance of an OkResult or a BadRequestResult:

[FunctionName("AddActor1")]
public static async Task<IActionResult> AddActor1(
    [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    dynamic data = JsonConvert.DeserializeObject(requestBody);

    string name = data.actorName; // get name from dynamic/JSON object

    if (name == null)
    {
        // Return a 400 bad request  result to the client
        return new BadRequestResult();
    }

    // Do some processing
    char firstLetter = name[0];

    // Return a 200 OK to the client
    return new OkResult();                
}

If you wanted to provide additional success/failure information you could use the OkObjectResult and BadRequestObjectResult classes instead, these allow you to provide additional contextual information to the client:

[FunctionName("AddActor2")]
public static async Task<IActionResult> AddActor2(
    [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    dynamic data = JsonConvert.DeserializeObject(requestBody);

    string name = data.actorName; // get name from dynamic/JSON object

    if (name == null)
    {
        // Return a 400 bad request result to the client with additional information
        return new BadRequestObjectResult("Please pass an actorName in the request body");
    }

    // Do some processing
    char firstLetter = name[0];

    // Return a 200 OK to the client with additional information
    return new OkObjectResult($"Actor {name} was added");
}

Automatically Returning Status Codes

In addition to manually returning status code instances, you can let the functions runtime take care of this for you.

For example, the following code will automatically return a “204 no content” if the function executes without throwing an exception, or a “500 internal server error” if an exception was thrown:

[FunctionName("AddActor3")]
public static async Task AddActor3(
    [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    dynamic data = JsonConvert.DeserializeObject(requestBody);

    string name = data.actorName; // get name from dynamic/JSON object

    // Do some processing
    char firstLetter = name[0]; // 500 internal server error if name is null

    // Auto return a 204 no content if no exception was thrown
}

In the preceding code, if the client fails to provide a actorName in the JSON, rather then getting a more helpful “400 bad request” (with optional additional message), they instead get a less useful “500 internal server error” status code and they have no idea what may have gone wrong or how to resolve it.

In this way, automatic status codes can be helpful if you want to write less code or perhaps use the return value of the function in a binding as in the following example:

[FunctionName("AddActor4")]
[return: Queue("new-actor-first-letter")]
public static async Task<string> AddActor4(
    [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    dynamic data = JsonConvert.DeserializeObject(requestBody);

    string name = data.actorName;

    return name.Substring(0,1); // add a new message to the queue containing the first letter of the name
}

Once again, the preceding function will return a 500 if there is an exception (e.g. actorName not provided in JSON) but will return a “200 OK” if no exception occurs (rather than the “204 no content” in the earlier example).

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Different Ways to Parse Http Request Data in Http-triggered Azure Functions

(This post refers to Azure Functions v2)

There are different ways to access both the request data and also request metadata when a HTTP-triggered Azure Function is executed.

Getting Query String Data in Azure Functions

Suppose we have the following class (e.g. in table storage):

public class PhotoMetadata
{
    public string PartitionKey { get; set; }
    public string RowKey { get; set; }
    public string FileName { get; set; }
    public string Keywords { get; set; }
}

We could write an Azure Function triggered by a HTTP GET that returns an item from a database by a querystring parameter called “id”:

[FunctionName("GetPhotoMetadata")]
public static IActionResult GetPhotoMetadata(
    [HttpTrigger(AuthorizationLevel.Function, "get")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    string id = req.Query["id"];

    if (string.IsNullOrWhiteSpace(id))
    {
        return new NotFoundResult();
    }

    PhotoMetadata metadata = LoadFromDatabase(id);

    return new OkObjectResult(metadata);
}

In the preceding code, to access querystring parameters use req.Query and specify the key you are looking for, in this example “id”.

If there is no value in the incoming request, id will be null and we return a NotFoundResult (404).

Getting HTTP POST JSON Request Data in Azure Functions

When it comes to accessing POSTed data, there are a number of options.

Manually Convert JSON Request Strings

The first option is to take control of the process at a lower level and read the posted data from the request body and parse the JSON into a dynamic C# object. [If you’re not familiar with dynamic C# check out my Dynamic C# Fundamentals Pluralsight course]

First we define a model that will represent the posted data (we don’t want to use the PhotoMetadata class as we don’t want clients specifying partition and row keys):

public class PhotoMetadataAdditionRequest
{
    public string FileName { get; set; }
    public string Keywords { get; set; }
}

Next we can write a function that will parse this incoming data:

[FunctionName("AddPhotoMetadata")]
public static async Task<IActionResult> AddPhotoMetadata(
    [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");


    log.LogInformation("You can get additional information about the request such as:");
    log.LogInformation($" length : {req.ContentLength}");
    log.LogInformation($" type   : {req.ContentType}");
    log.LogInformation($" https  : {req.IsHttps}");
    log.LogInformation($" host   : {req.Host}");


    // read the contents of the posted data into a string
    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();

    // use Json.NET to deserialize the posted JSON into a C# dynamic object
    dynamic data = JsonConvert.DeserializeObject(requestBody);

    // data validation omitted for demo purposes

    // extract data from the dynamic object into strongly typed object
    PhotoMetadata metadata = new PhotoMetadata
    {
        FileName = data.fileName, // notice the camel case (lowercase f)
        PartitionKey = "landscapes",
        RowKey = Guid.NewGuid().ToString(),
        Keywords = data.keywords // notice the camel case (lowercase k)
    };

    SaveToDatabase(metadata);

    return new OkObjectResult(metadata.RowKey);
}

Notice in the preceding code that you can also access information about the request such as req.ContentLength. Also note the lowercase f and k in data.fileName and data.keywords.

We can post the following JSON to the function:

{
    "fileName": "IMG0382435.jpg",
    "keywords": "landscape, sky, sunset"
}

Automatically Bind to Strongly Types POCOs in Azure HTTP Functions

You can also let the runtime auto-convert the POSTed JSON into a specified C# type:

[FunctionName("AddPhotoMetadata")]
public static IActionResult AddPhotoMetadata(
    [HttpTrigger(AuthorizationLevel.Function, "post")] PhotoMetadataAdditionRequest metadataAdditionRequest,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    log.LogInformation($" FileName : {metadataAdditionRequest.FileName}");
    log.LogInformation($" Keywords : { metadataAdditionRequest.Keywords}");

    PhotoMetadata metadata = new PhotoMetadata
    {
        FileName = metadataAdditionRequest.FileName,
        PartitionKey = "landscapes",
        RowKey = Guid.NewGuid().ToString(),
        Keywords = metadataAdditionRequest.Keywords
    };

    SaveToDatabase(metadata);

    return new OkObjectResult(metadata.RowKey);
}

In the preceding code, instead of binding to a HttpRequest object,  we bind to the PhotoMetadataAdditionRequest. Behind the scenes the JSON will be automatically deserialized into a PhotoMetadataAdditionRequest object.

Note that if you have malformed JSON you may get errors. For example if the “fileName” item in the JSON was misspelt as “file” then the FileName property of the PhotoMetadata would end up being set to null but the function body would still execute. If you had an int in the POCO but the POSTed JSON had a string (e.g. “hello”) instead of a number, then the runtime cannot bind a “hello” to an int – in this case your function body code will not even execute and you get an error from the runtime such as: “System.Private.CoreLib: Exception while executing function: AddPhotoMetadata. Microsoft.Azure.WebJobs.Host: Exception binding parameter 'metadataAdditionRequest'. System.Private.CoreLib: Input string was not in a correct format.” (and a 500 will status be returned to the client).

If you were handling things at a lower level (e.g. with the dynamic approach) you could perhaps provide a default value, do some extra logging, etc.

Accessing HTTP Request Metadata When Auto-binding to POCOs

If you want to do automatic binding and also want to get request metadata, you can simply add an extra parameter of type HttpRequest:

[FunctionName("AddPhotoMetadata")]
public static IActionResult AddPhotoMetadata(
    [HttpTrigger(AuthorizationLevel.Function, "post")] PhotoMetadataAdditionRequest metadataAdditionRequest,
    HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    log.LogInformation("You can get additional information about the request such as:");
    log.LogInformation($" length : {req.ContentLength}");
    log.LogInformation($" type   : {req.ContentType}");
    log.LogInformation($" https  : {req.IsHttps}");
    log.LogInformation($" host   : {req.Host}");

    log.LogInformation($" FileName : {metadataAdditionRequest.FileName}");
    log.LogInformation($" Keywords : { metadataAdditionRequest.Keywords}");

    PhotoMetadata metadata = new PhotoMetadata
    {
        FileName = metadataAdditionRequest.FileName,
        PartitionKey = "landscapes",
        RowKey = Guid.NewGuid().ToString(),
        Keywords = metadataAdditionRequest.Keywords
    };

    SaveToDatabase(metadata);

    return new OkObjectResult(metadata.RowKey);
}

Posting Form Data to Azure Functions

In addition to POSTing JSON content to an Azure Function, you can also POST form data and access the HttpRequest.Form property:

[FunctionName("AddPhotoMetadata")]
public static IActionResult AddPhotoMetadata(
    [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    log.LogInformation("You can get additional information about the request such as:");
    log.LogInformation($" length : {req.ContentLength}");
    log.LogInformation($" type   : {req.ContentType}");
    log.LogInformation($" https  : {req.IsHttps}");
    log.LogInformation($" host   : {req.Host}");

    PhotoMetadata metadata = new PhotoMetadata
    {
        FileName = req.Form["fileName"], // access form data
        PartitionKey = "landscapes",
        RowKey = Guid.NewGuid().ToString(),
        Keywords = req.Form["keywords"]  // access form data
    };

    SaveToDatabase(metadata);

    return new OkObjectResult(metadata.RowKey);
}

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Customizing C# Object Member Display During Debugging

In a previous post I wrote about Customising the Appearance of Debug Information in Visual Studio with the DebuggerDisplay Attribute. In addition to controlling the high level  debugger appearance of an object we can also exert a lot more control over how the object appears in the debugger by using the DebuggerTypeProxy attribute.

For example, suppose we have the following (somewhat arbitrary) class:

class DataTransfer
{
    public string Name { get; set; }
    public string ValueInHex { get; set; }
}

By default, in the debugger it would look like the following:

Default Debugger View

To customize the display of the object members, the DebuggerTypeProxy attribute can be applied.

The first step is to create a class to act as a display proxy. This class takes the original object as part of the constructor and then exposes the custom view via public properties.

For example, suppose that we wanted a decimal display of the hex number that originally is stored in a string property in the original DataTransfer object:

class DataTransferDebugView
{
    private readonly DataTransfer _data;

    public DataTransferDebugView(DataTransfer data)
    {
        _data = data;
    }

    public string NameUpper => _data.Name.ToUpperInvariant();
    public string ValueDecimal
    {
        get
        {
            bool isValidHex = int.TryParse(_data.ValueInHex, System.Globalization.NumberStyles.HexNumber, null, out var value);

            if (isValidHex)
            {
                return value.ToString();
            }

            return "INVALID HEX STRING";
        }
    }
}

Once this view object is defined, it can be selected by decorating the DataTransfer class with the DebuggerTypeProxy attribute as follows:

[DebuggerTypeProxy(typeof(DataTransferDebugView))]
class DataTransfer
{
    public string Name { get; set; }
    public string ValueInHex { get; set; }
}

Now in the debugger, the following can be seen:

Custom debug view showing hex value as a decimal

Also notice in the preceding image, that the original object view is available by expanding the Raw View section.

To learn more about C# attributes and even how to create your own custom ones, check out my C# Attributes: Power and Flexibility for Your Code course at Pluralsight.

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MSTest V2

In the (relatively) distant past, MSTest was often used by organizations because it was provided by Microsoft “in the box” with Visual Studio/.NET. Because of this, some organizations trusted MSTest over open source testing frameworks such as NUnit. This was at a time when the .NET open source ecosystem was not as advanced as it is today and before Microsoft began open sourcing some of their own products.

Nowadays MSTest is cross-platform and open source and is known as MSTest V2, and as the documentation states: “is a fully supported, open source and cross-platform implementation of the MSTest test framework with which to write tests targeting .NET Framework, .NET Core and ASP.NET Core on Windows, Linux, and Mac.”.

MSTest V2 provides typical assert functionality such as asserting on the values of: strings, numbers, collections, thrown exceptions, etc. Also like other testing frameworks, MSTest V2 allows the customization of the test execution lifecycle such as the running of additional setup code before each test executes. The framework also allows the creation of data driven tests (a single test method executing  multiple times with different input test data) and the ability to extend the framework with custom asserts and custom test attributes.

You can find out more about MSTest V2 at the GitHub repository, the documentation, or check out my Pluralsight course: Automated Testing with MSTest V2.

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Prevent Secrets From Accidentally Being Committed to Source Control in ASP.NET Core Apps

One problem when dealing with developer “secrets” in development is accidentally checking them into source control. These secrets could be connection strings to dev resources, user IDs, product keys, etc.

To help prevent this from accidentally happening, the secrets can be stored outside of the project tree/source control repository. This means that when the code is checked in, there will be no secrets in the repository.

Each developer will have their secrets stored outside of the project code. When the app is run, these secrets can be retrieved at runtime from outside the project structure.

One way to accomplish this in ASP.NET Core  projects is to make use of the Microsoft.Extensions.SecretManager.Tools NuGet package to allow use of the command line tool. (also if you are targeting .NET Core 1.x , install the Microsoft.Extensions.Configuration.UserSecrets NuGet package).

Setting Up User Secrets

After creating a new ASP.NET Core project, add a tools reference to the NuGet package to the project, this will add the following item in the project file:

<DotNetCliToolReference Include="Microsoft.Extensions.SecretManager.Tools" Version="2.0.0" />

Build the project and then right click the project and you will see a new item called “Manage User Secrets” as the following screenshot shows:

Managing user secrets in Visual Studio

Clicking menu item will open a secrets.json file and also add an element named UserSecretsId to the project file. The content of this element is a GUID, the GUID is arbitrary but should be unique for each and every project.

<UserSecretsId>c83d8f04-8dba-4be4-8635-b5364f54e444</UserSecretsId>

User secrets will be stored in the secrets.json file which will be in %APPDATA%\Microsoft\UserSecrets\<user_secrets_id>\secrets.json on Windows or ~/.microsoft/usersecrets/<user_secrets_id>/secrets.json on Linux and macOS. Notice these paths contain the user_secrets_id that matches the GUID in the project file. In this way each project has a separate set of user secrets.

The secrets.json file contains key value pairs.

Managing User Secrets

User secrets can be added by editing the json file or by using the command line (from the project directory).

To list user secrets type: dotnet user-secrets list At the moment his will return “No secrets configured for this application.”

To set (add) a secret: dotnet user-secrets set "Id" "42"

The secrets.json file now contains the following:

{
  "Id": "42"
}

Other dotnet user-secrets  commands include:

  • clear - Deletes all the application secrets
  • list - Lists all the application secrets
  • remove - Removes the specified user secret
  • set - Sets the user secret to the specified value

Accessing User Secrets in Code

To retrieve users secrets, in the startup class, access the item by key, for example:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    var secretId = Configuration["Id"]; // returns 42
}

One thing to bear in mind is that secrets are not encrypted in the secrets.json file, as the documentation states: “The Secret Manager tool doesn't encrypt the stored secrets and shouldn't be treated as a trusted store. It's for development purposes only. The keys and values are stored in a JSON configuration file in the user profile directory.” & “You can store and protect Azure test and production secrets with the Azure Key Vault configuration provider.”

There’s a lot more information in the documentation and if you plan to use this tool you should read through it.

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