Initial dotnet Reaction SDK

[danielgerlag]

Reaction SDK for Drasi

This library provides the building blocks and infrastructure to implement a Drasi Reaction in .NET

Getting started

Install the package

dotnet add package Drasi.Reaction.SDK

Basic example

The following example simply breaks down and logs the various parts of the incoming change event from a Continuous Query.

var builder = new ReactionBuilder();

builder.UseChangeEventHandler(async (evt, queryConfig) =>
{
    Console.WriteLine($"Received change event from query {evt.QueryId} sequence {evt.Sequence}");
    
    foreach (var item in evt.AddedResults)
        Console.WriteLine($"Added result: {item}");

    foreach (var item in evt.UpdatedResults)
        Console.WriteLine($"Updated result, before {item.Before}, after {item.After}");

    foreach (var item in evt.DeletedResults)
        Console.WriteLine($"Deleted result: {item}");

});

var reaction = builder.Build();
await reaction.StartAsync();

A more advanced example

The following example illustrates

• Retrieving a configuration value from the Reaction manifest
• Defining a custom per query configuration object
• Parsing the per query configuration object from Yaml
• Process change events form thw query
• Process control events (start, stop, etc.) from the query

var reaction = new ReactionBuilder<MyQueryConfig>()
    .UseChangeEventHandler<MyChangeHandler>()               // Use your custom change handler
    .UseControlEventHandler<MyControlSignalHandler>()       // Use your custom control signal handler
    .UseYamlQueryConfig()                                   // Parse the per query configuration from Yaml
    .ConfigureServices((services) =>                        // Register your own services
    {
        services.AddSingleton<MyService>();
    })
    .Build();

// Start the reaction
await reaction.StartAsync();

// Define a custom per query configuration object
class MyQueryConfig
{
    [JsonPropertyName("greeting")]
    public string? Greeting { get; set; }
}

// Your own internal service
class MyService
{
    private readonly string _connectionString;

    public MyService(IConfiguration configuration)
    {
        // Retrieve the connection string from the Reaction configuration
        _connectionString = configuration["MyConnectionString"];
    }

    public void DoSomething()
    {
        Console.WriteLine("Doing something");
    }
}

// Define a custom change handler, that uses your service
class MyChangeHandler : IChangeEventHandler<MyQueryConfig>
{   
    private readonly MyService _service;
    private readonly ILogger<MyChangeHandler> _logger;

    public MyChangeHandler(MyService service, ILogger<MyChangeHandler> logger)
    {
        _service = service;
        _logger = logger;
    }

    public async Task HandleChange(ChangeEvent evt, MyQueryConfig? queryConfig)
    {
        _logger.LogInformation($"Received change event from query {evt.QueryId} sequence {evt.Sequence}. Query greeting is {queryConfig?.Greeting}");
        _logger.LogInformation($"Full event: {evt.ToJson()}");
        _service.DoSomething();
    }
}

// Define a custom control signal handler
class MyControlSignalHandler : IControlEventHandler<MyQueryConfig>
{
    private readonly ILogger<MyControlSignalHandler> _logger;

    public MyControlSignalHandler(ILogger<MyControlSignalHandler> logger)
    {
        _logger = logger;
    }

    public async Task HandleControlSignal(ControlEvent evt, MyQueryConfig? queryConfig)
    {
        _logger.LogWarning($"Received control signal: {evt.ControlSignal?.Kind} for query {evt.QueryId}. Query greeting is {queryConfig?.Greeting}");
    }
}

[ruokun-niu]

Do we have to specify a queryconfig object in order to define the HandleChange method?

[danielgerlag]

No, the default is System.Object if you do not specify one.

[ruokun-niu]

Great!

[ruokun-niu]

Typo