Create a Message Consumer

A message consumer, the most common consumer type, is a class that consumes one or more messages types. For each message type, the class implements the IConsumer<TMessage> interface that has a single Consume method.

Creating a message consumer

To create a message consumer:

Create a new project

Create a new project (or use an existing project) using the class library template. If you’re using an existing project, skip this step.

dotnet new classlib -o ./src/MyProject.Components
dotnet sln add ./src/MyProject.Components

Reference the Contracts project

Add a reference to the message contract project using your IDE, or by running the following command from the command line.

dotnet reference add ./src/MyProject.Contracts --project ./src/MyProject.Components

Create a consumer class

Create a new class in the MyProject.Components project. To keep components organized, create a new folder for consumers.

namespace MyProject.Components.Consumers;

using MassTransit;
using MyProject.Contracts;

public class CreateCustomerConsumer :
    IConsumer<CreateCustomer>
{
    public async Task Consume(ConsumeContext<CreateCustomer> context)
    {
        // Handle the message
    }
}

Inject constructor dependencies

Message consumers can have dependencies injected into their constructors. For example, if the consumer needs to access a database, inject the database context into the consumer’s constructor. You may also want to inject other services, such as an ILogger<T> instance.

namespace MyProject.Components.Consumers;

using MassTransit;
using Microsoft.EntityFrameworkCore;
using MyProject.Contracts;

public class CreateCustomerConsumer :
    IConsumer<CreateCustomer>
{
    readonly DbContext _dbContext;
    readonly ILogger<CreateCustomerConsumer> _logger;

    public CreateCustomerConsumer(DbContext dbContext, ILogger<CreateCustomerConsumer> logger)
    {
        _dbContext = dbContext;
        _logger = logger;
    }

    public async Task Consume(ConsumeContext<CreateCustomer> context)
    {
        _logger.LogInformation("Creating customer {CustomerName}", context.Message.CustomerName);

        await _dbContext.Customers.AddAsync(new Customer(context.Message.CustomerName));
        await _dbContext.SaveChangesAsync();

        await context.Publish(new CustomerCreated(context.Message.CustomerName));
    }
}

Next steps

Once you’ve created a message consumer, you can learn about testing a consumer to verify that it’s working correctly.