[rabbitmq-discuss] Binding to topic exchange with a negation wildcard

Thu Sep 13 15:53:26 BST 2012

We would find a regular expression matching option for topic exchanges
most useful.

My 2 cents :)

Michael

On 9/13/12 4:40 AM, "Simon MacMullen" <simon at rabbitmq.com> wrote:

>On 12/09/2012 8:37PM, Dave Curylo wrote:
>> Is it possible to bind a queue to a topic exchange with a condition that
>> the topic does NOT match a certain wildcard?
>
>The topic exchange doesn't have that logic. But you can fake it with the
>alternate exchange feature, at the cost of a few more exchanges.
>
>Declare a fanout exchange you'll publish to (let's call it
>"my-exchange"). Declare a fanout exchange called "junk".
>
>The when each consumer declares a queue, it also declares a topic
>exchange and a fanout exchange. The alternate-exchange for the topic
>exchange should be set to the fanout exchange. It then binds the topic
>exchange to "my-exchange", and "junk" to the topic exchange, with a
>routing key equal to the topics it doesn't want.
>
>Thus messages with the "bad" routing key go:
>
>   [my-exchange] -> [per-consumer-topic] -> [junk]
>
>and the rest go:
>
>   [my-exchange] -> [per-consumer-topic] -> [per-consumer-fanout] ->
>[per-consumer-queue]
>
>I think that's the simplest you can make it. But exchanges are cheap in
>general, it's just routing logic.
>
>But I wonder whether some sort of more explicit negation feature would
>be feasible / useful. Hmm.
>
>Cheers, Simon
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