This provides an example REST backend built in C# using .NET Core 2.1 for use with the Getting Started with Astra UI.

Contributors:

Objectives

  • How to connect to Astra via the Secure Connect Bundle
  • How to manage a Cassandra Session within a .NET web application

Project Layout

This sample also contains several interesting files that worth noting specifically:

  • Services/AstraService.cs - This file contains all the logic for connecting to the Astra database using the secure connect bundle.
  • Startup.cs - This file contains the logic for adding a singleton for the Session object for reuse across our application.

See here for additional details on how the session object in Cassandra works and why it is best practice to only have a single Session object per application

  • schema.cql - The database schema required for the Astra keyspace

  • Controllers/InstrumentController.cs - If you would like to see how to implement paging in C# then this would be the place to look. Paging in Cassandra is different than what you are likely used to so it is beneficial to read this article describing how paging works with Cassandra.

How this Sample Works

This is am example .NET Core Web API backend for use with the Astra Getting Started UI which is found here.

This application serves as the connection between the UI website and an underlying Astra database.

It has Swagger installed so once it is running you can look at the Swagger UI here:

http://localhost:5000/swagger/index.html#/

Connecting to Astra with a Secure Connect Bundle

To see how to connect to Astra using the Secure Connect Bundle you can look at the ConnectToAstra() method in Services/AstraService.cs. In this method you will find the code which:

  1. Creates a Cluster instance using the builder.

    var session = Cluster.Builder()

  2. Specifies the local file path to the Secure Connect Bundle ZIP file that has been downloaded from your Astra Database.

    .WithCloudSecureConnectionBundle(secureConnectBundlePath)

  3. Set the username and password for your Astra Database

    .WithCredentials(username, password)

  4. Set the default Consistency Level to LOCAL_QUORUM. LOCAL_QUORUM is the only supported consistency level for Astra queries.

    .WithQueryOptions(new QueryOptions().SetConsistencyLevel(ConsistencyLevel.LocalQuorum))

  5. Build the Cluster object then connect to your Astra database specifying the keyspace to use.

    .Build().Connect(keyspace);

Once you have completed all these steps you will now have a fully configured, connected, and ready to run CQL queries.

Managing Cassandra Session Within a .NET Web Application

Creation of Session objects within an application is an expensive process as they take awhile to initialize and become aware of the clusters topology. Due to this it is a best practice to create a Session object once per application and reuse it throughout the entire lifetime of that application. When building an ASP.NET Core application as shown this is easily supported through the use of singleton and .NET Core's built in Dependency Injection mechanisms.

For our Web API endpoints we created a singleton instance of our AstraService object inside the ConfigureServices() method in Startup.cs using the following code:

services.AddSingleton(typeof(Interfaces.IDataStaxService), typeof(Services.AstraService));

This code specifies that we are adding a singleton instance of AstraService for any dependency requiring an object instantiating the Interfaces.IDataStaxService interface.

To use this within our controllers, we need to specify a property on the constructor of the controller that requires the Interfaces.IDataStaxService interface as shown below.

public CredentialsController(IDataStaxService service) { Service = service; }

With each call to the CredentialsController the AstraService singleton we created at startup will be passed to the constructor. This mechanism of dependency injection allows us a simple mechanism to use a single Session object throughout the entirety of the application lifecycle.

Setup and Running

Prerequisites

  • .NET Core 2.1
  • An Astra compatible C# driver, instructions may be found here to install this locally.
  • An Astra database with the CQL schema located in schema.cql already added.
  • The username, password, keyspace name, and secure connect bundle downloaded from your Astra Database. For information on how to obtain these credentials please read the documentation found here.

Running

This application is a .NET 2.1 web application configured to serve it's web application via the Kestrel web server. This sample can be run from the root directory using:

dotnet run

This will startup the application running on http://localhost:5000

You will know that you are up and working when you get the following in your terminal window:

Hosting environment: Development
Content root path: /Users/dave.bechberger/Documents/projects/bechbd/getting-started-with-astra-csharp
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.