15. RabbitMQ Setup & Implementing Event Bus with CAP

First, install Erlang from download, and then install RabbitMQ from download.
Navigate to the installation folder (C:\Users\ASD\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\RabbitMQ Server) and run the RabbitMQ Service - start service. Check if the service is running in Windows Services.
Next, open the RabbitMQ Command Prompt (sbin dir) and run the command rabbitmq-plugins.bat enable rabbitmq_management.

Now, open the link http://127.0.0.1:15672/ and log in using the username and password guest.

(Alternatively, you can use Docker without installing Erlang and RabbitMQ clients. To do this, pull the RabbitMQ Docker image with docker pull rabbitmq:3.10-management and then run the RabbitMQ container using docker run -d --name rabbitmq -p 5672:5672 -p 15672:15672 rabbitmq:3-management. For more details, visit Rabbitmq docker setup guide).

Event Bus Architecture

For more information on the Event Bus architecture, check out this article: efficient-event-communication-implementing-event-bus-and-outbox-patterns-with-cap-in-net-core-microservices

First, create a new blank solution, and then add two API projects beneath it named MessagePublisher and MessageConsumer. Afterward,

For MessagePublisher Project:

Install the following NuGet packages in publisher projects:

DotNetCore.CAP
DotNetCore.CAP.Dashboard
DotNetCore.CAP.RabbitMQ
DotNetCore.CAP.SqlServer
Microsoft.AspNetCore.OpenApi
Microsoft.EntityFrameworkCore.SqlServer
Microsoft.EntityFrameworkCore
Microsoft.EntityFrameworkCore.Tools

Or, you can install them all at once by adding the following to your .csproj file:

<ItemGroup>
  <PackageReference Include="DotNetCore.CAP" Version="8.3.3" />
  <PackageReference Include="DotNetCore.CAP.Dashboard" Version="8.3.3" />
  <PackageReference Include="DotNetCore.CAP.RabbitMQ" Version="8.3.3" />
  <PackageReference Include="DotNetCore.CAP.SqlServer" Version="8.3.3" />
  <PackageReference Include="Microsoft.EntityFrameworkCore" Version="9.0.2" />
  <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="9.0.2" />
  <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="9.0.2">
    <PrivateAssets>all</PrivateAssets>
    <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
  </PackageReference>
  <PackageReference Include="Swashbuckle.AspNetCore" Version="6.6.2" />
</ItemGroup>

Add an entity named Customer:

using System.ComponentModel.DataAnnotations;
 
namespace MessagePublisher.Entities
{
    public class Customer : CustomerInsert
    {
        [Key]
        public int Id { get; set; }
    }
 
    public class CustomerInsert
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string MobilNumber { get; set; }
    }
}

Now add a Service class named CustomerService and its interface ICustomerService:

public interface ICustomerService
{
    Task<bool> AddCustomer(CustomerInsert order);
}

public class CustomerService : ICustomerService
{
    private readonly ServiceDbContext _dbContext;
    private readonly ICapPublisher _capPublisher;
 
    public CustomerService(ServiceDbContext dbContext, ICapPublisher capPublisher)
    {
        this._dbContext = dbContext;
        _capPublisher = capPublisher;
    }
 
    public async Task<bool> AddCustomer(CustomerInsert customerInsert)
    {
        Customer customer = new Customer
        {
            FirstName = customerInsert.FirstName,
            LastName = customerInsert.LastName,
            MobilNumber = customerInsert.MobilNumber,
        };
 
        await _dbContext.AddAsync(customer);
        await _dbContext.SaveChangesAsync();
        var content = JsonSerializer.Serialize(customer);
        await _capPublisher.PublishAsync<string>("CustomerAdded", content);
        return true;
    }
}

Now add an API-based controller named CustomerController:

[Route("api/[controller]")]
[ApiController]
public class CustomerController : ControllerBase
{
    private readonly ICustomerService _customerService;
 
 
    public CustomerController(ICustomerService customerService)
    {
        _customerService = customerService;
    }
 
    [HttpPost]
    public async Task<IActionResult> Post([FromBody] CustomerInsert customer)
    {
        try
        {
            return Ok(await _customerService.AddCustomer(customer));
        }
        catch (Exception ex)
        {
            throw;
        }
    }
}

Add a DbContext name ServiceDbContext

public class ServiceDbContext : DbContext
{
    public DbSet<Customer> Customers { get; set; }
    public ServiceDbContext(DbContextOptions<ServiceDbContext> options)
        : base(options)
    {
    }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
    }
}

Add a line into appsetting.json

"ConnectionStrings": {
  "DefaultConnection": "Server=.\\SQLEXPRESS; Database=EventBusDB; Trusted_Connection=True; TrustServerCertificate=True;"
}

Modify program.cs

// DBContext
builder.Services.AddDbContext<ServiceDbContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));
 
// RabbitMQ Setup
builder.Services.AddCap(options =>
{
    options.UseEntityFramework<ServiceDbContext>();
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"));
    options.UseDashboard(path => path.PathMatch = "/cap-dashboard");
    options.UseRabbitMQ(options =>
    {
        options.ConnectionFactoryOptions = options =>
        {
            options.Ssl.Enabled = false;
            options.HostName = "localhost";
            options.UserName = "guest";
            options.Password = "guest";
            options.Port = 5672;
        };
    });
});
 
/// Service
builder.Services.AddScoped<ICustomerService, CustomerService>();

Apply the migration only to the Publisher project by running:
```
dotnet ef migrations add InitialCreate
dotnet ef database update
```
(Make sure the dotnet-ef tool is installed globally with [dotnet tool install --global dotnet-ef]).

For MessageConsumer Project:

Install the following NuGet packages in consumer projects:

DotNetCore.CAP
DotNetCore.CAP.Dashboard
DotNetCore.CAP.RabbitMQ
DotNetCore.CAP.SqlServer
Microsoft.EntityFrameworkCore.SqlServer

Or, you can install them all at once by adding the following to your .csproj file:

<ItemGroup>
<PackageReference Include="DotNetCore.CAP" Version="8.3.3" />
<PackageReference Include="DotNetCore.CAP.Dashboard" Version="8.3.3" />
<PackageReference Include="DotNetCore.CAP.RabbitMQ" Version="8.3.3" />
<PackageReference Include="DotNetCore.CAP.SqlServer" Version="8.3.3" />
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="9.0.2" />
<PackageReference Include="Swashbuckle.AspNetCore" Version="6.6.2" />

```

Add a subscriber named CustomerAddedEventSubscriber:

public class CustomerAddedEventSubscriber : ICapSubscribe
{
    [CapSubscribe("CustomerAdded")]
    public void Consumer(JsonElement customerData)
    {
        Console.WriteLine(customerData);
    }
}

Add a DbContext named MainDbContext

public class MainDbContext : DbContext
{
    public MainDbContext(DbContextOptions<MainDbContext> options)
        : base(options)
    {
    }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
    }
}

Add a line into appsetting.json

"ConnectionStrings": {
  "DefaultConnection": "Server=.\\SQLEXPRESS; Database=TempoDB; Trusted_Connection=True; TrustServerCertificate=True;"
}

Modify in program.cs

// DbContext
builder.Services.AddDbContext<MainDbContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));
 
// Cap Setup
builder.Services.AddCap(options =>
{
    options.UseEntityFramework<MainDbContext>();
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"));
    options.UseDashboard(path => path.PathMatch = "/cap-dashboard");
    options.UseRabbitMQ(options =>
    {
        options.ConnectionFactoryOptions = options =>
        {
            options.Ssl.Enabled = false;
            options.HostName = "localhost";
            options.UserName = "guest";
            options.Password = "guest";
            options.Port = 5672;
        };
    });
});
 
// Event Handler Service
builder.Services.AddSingleton<CustomerAddedEventSubscriber>();

After starting both projects at the same time, two CAP tables will be automatically generated: cap.Published and cap.Received. If there are two different databases, it will create two different cap.Published and cap.Received tables on each database. To view the dashboard in each project, visit http://localhost:xxxx/cap-dashboard.

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15. RabbitMQ Setup & Implementing Event Bus with CAP

Event Bus Architecture

For MessagePublisher Project:

For MessageConsumer Project: