Exercise - Retrieve a message from the queue - Learn

10 minutes

Let's complete the application by writing code to read the next message in the queue, process it, and then delete it from the queue.

We're going to place the code into the application and run it when a user selects the appropriate menu items. In a real-world scenario, this code should be put in its own application dedicated to receiving and processing messages.

Peeking at the next message

Let's add a new method that peeks at the next message from the queue.

Open Program.cs source file in your editor.
Find the PeekMessageAsync method in the application and delete the line throwing a NotImplementedException.

Add the following code to the method. This code peeks at the next message on the queue and prints out some information about the message.

        Response<PeekedMessage> response = await queueClient.PeekMessageAsync();
        PeekedMessage message = response.Value;

        Console.WriteLine($"Message id  : {message.MessageId}");
        Console.WriteLine($"Inserted on : {message.InsertedOn}");
        Console.WriteLine("We are only peeking at the message, so another consumer could dequeue this message");

Receiving and processing messages

Add code to receive and process a message in the application.

Find the ReceiveMessageAsync method in the application and delete the line throwing a NotImplementedException.

At the top of the ReceiveMessageAsync method, add the following lines of code to get a message from the queue.

Response<QueueMessage> response = await queueClient.ReceiveMessageAsync();
QueueMessage message = response.Value;

Add the following lines of code below the two lines you just added to the method. This code prints out some properties about the received message, including the body of the raw message which will be in JSON format.
```
Console.WriteLine($"Message id    : {message.MessageId}");
Console.WriteLine($"Inserted on   : {message.InsertedOn}");
Console.WriteLine($"Message (raw) : {message.Body}");
```

To deserialize the message content into an object that we can work with in our code, add the ToObjectFromJson method on the Body property of the QueueMessage object. Add the following lines to the method.

NewsArticle article = message.Body.ToObjectFromJson<NewsArticle>();
Console.WriteLine("News Article");
Console.WriteLine($"-  Headline : {article.Headline}");
Console.WriteLine($"-  Location : {article.Location}");

Finally, when we have processed the message, we need to delete the message from the queue so no other consumers process it. Add the following code to the end of the ReceiveMessageAsync method.

Console.WriteLine("The processing for this message is just printing it out, so now it will be deleted");
await queueClient.DeleteMessageAsync(message.MessageId, message.PopReceipt);
Console.WriteLine($"Message deleted");

The complete method should look like this:

static async Task ReceiveMessageAsync(QueueClient queueClient)
{
    Response<QueueMessage> response = await queueClient.ReceiveMessageAsync();
    QueueMessage message = response.Value;

    Console.WriteLine($"Message id    : {message.MessageId}");
    Console.WriteLine($"Inserted on   : {message.InsertedOn}");
    Console.WriteLine($"Message (raw) : {message.Body}");

    NewsArticle article = message.Body.ToObjectFromJson<NewsArticle>();
    Console.WriteLine("News Article");
    Console.WriteLine($"-  Headline : {article.Headline}");
    Console.WriteLine($"-  Location : {article.Location}");

    Console.WriteLine("The processing for this message is just printing it out, so now it will be deleted");
    await queueClient.DeleteMessageAsync(message.MessageId, message.PopReceipt);
    Console.WriteLine($"Message deleted");
}

Execute the application

The code is now complete. It can now send and retrieve messages.

First, build the application.
```
dotnet build
```
Run the application
```
dotnet run
```

Use the menu to experiment with adding messages to, peeking at, and receiving messages on the queue. Your sample output should look similar to the following.

What operation would you like to perform?
  1 - Send message
  2 - Peek at the next message
  3 - Receive message
  X - Exit program
1

Enter headline:
World leaders to meet at economic summit
Enter location:
Paris, France
Message sent.  Message id=8f5b9bc7-3e7f-448b-9787-508636963938  Expiration time=10/14/2021 9:01:58 PM +00:00

What operation would you like to perform?
  1 - Send message
  2 - Peek at the next message
  3 - Receive message
  X - Exit program
2

Message id  : 8f5b9bc7-3e7f-448b-9787-508636963938
Inserted on : 10/7/2021 9:01:58 PM +00:00
We are only peeking at the message, so another consumer could dequeue this message
What operation would you like to perform?
  1 - Send message
  2 - Peek at the next message
  3 - Receive message
  X - Exit program
3

Message id    : 8f5b9bc7-3e7f-448b-9787-508636963938
Inserted on   : 10/7/2021 9:01:58 PM +00:00
Message (raw) : {"Headline":"World leaders to meet at economic summit","Location":"Paris, France"}
News Article
-  Headline : World leaders to meet at economic summit
-  Location : Paris, France
The processing for this message is just printing it out, so now it will be deleted
Message deleted
What operation would you like to perform?
  1 - Send message
  2 - Peek at the next message
  3 - Receive message
  X - Exit program
X

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