c# - 为什么要在 RabbitMQ 中声明 Exchange？

Question

我正在使用 RabbitMQ 进行一个项目。我的代码如下。

制作人:

public static void Main()
{
    var factory = new ConnectionFactory() { HostName = "localhost" };
    using (var connection = factory.CreateConnection())
    {
        using (var channel = connection.CreateModel())
        {
            channel.QueueDeclare("hello", false, false, false, null);

            string message = "Hello World!";
            var body = Encoding.UTF8.GetBytes(message);

            channel.BasicPublish("", "hello", null, body);
            Console.WriteLine(" [x] Sent {0}", message);
        }
    }
}

Consumer with Exchange 声明:

public static void Main()
{
    var factory = new ConnectionFactory() { HostName = "localhost" };
    using (var connection = factory.CreateConnection())
    {
        using (var channel = connection.CreateModel())
        {
            channel.ExchangeDeclare("hello", "direct",false, false, false, null);
            channel.QueueDeclare("hello", false, false, false, null);

            var consumer = new QueueingBasicConsumer(channel);
            channel.BasicConsume("hello", true, consumer);

            Console.WriteLine(" [*] Waiting for messages." +
                                     "To exit press CTRL+C");
            while (true)
            {
                var ea = (BasicDeliverEventArgs)consumer.Queue.Dequeue();

                var body = ea.Body;
                var message = Encoding.UTF8.GetString(body);
                Console.WriteLine(" [x] Received {0}", message);
            }
        }
    }

Consumer without Exchange 声明:

public static void Main()
{
    var factory = new ConnectionFactory() { HostName = "localhost" };
    using (var connection = factory.CreateConnection())
    {
        using (var channel = connection.CreateModel())
        {
            channel.QueueDeclare("hello", false, false, false, null);

            var consumer = new QueueingBasicConsumer(channel);
            channel.BasicConsume("hello", true, consumer);

            Console.WriteLine(" [*] Waiting for messages." +
                                     "To exit press CTRL+C");
            while (true)
            {
                var ea = (BasicDeliverEventArgs)consumer.Queue.Dequeue();

                var body = ea.Body;
                var message = Encoding.UTF8.GetString(body);
                Console.WriteLine(" [x] Received {0}", message);
            }
        }
    }

两种消费者代码都运行良好，那么声明交换的主要用途是什么？我很迷惑。谁能解释一下？

Answer 1

发布到队列 只允许您实现基本的发布-订阅场景，其中生产者和消费者使用确切的队列。在多个消费者的情况下，单个消息队列分布在多个消费者之间。

发布到 exchanges 可以让您创建复杂的场景，因为在 exchange 和队列之间有routing。

例如，扇出交换将消息路由到所有绑定(bind)队列。这样，您可以拥有一个生产者和多个消费者，并且每条消息都被独立复制到所有绑定(bind)队列并独立接收。

交换的另一个示例，主题交换 根据消息中的路由键 和队列上的模式将消息路由到绑定(bind)队列。这引入了一种有趣的可能性，即标记消息并有条件地传递它们。

有关交换类型及其配置文件的完整引用，请参阅文档:

https://www.rabbitmq.com/tutorials/amqp-concepts.html

https://www.rabbitmq.com/getstarted.html