# Selective Consumer

> Only receive messages that match your criteria — filter at subscription time, not after.

- **Category**: Integration
- **Subcategory**: Messaging Endpoints
- **Canonical URL**: https://designpattern.fyi/patterns/selective_consumer/

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## Description
Clean, reusable architecture pattern.


## Use Cases
Alerting system — subscribes to the transactions topic with selector amount > 50000 AND region = 'EMEA'. Receives only large EMEA transactions for compliance review. Does not see small transactions or non-EMEA activity. Broker-side filtering keeps the alert handler lean.





## Trade-offs


### Advantages

- Broker-side filtering — consumer receives only relevant messages, zero processing waste

- Consumer logic stays simple — no if/else routing guards needed

- Reduces consumer resource usage (CPU, memory, network)

- Multiple consumers with different selectors can share one topic




### Considerations & Drawbacks

- Not all brokers support rich selector expressions (check your broker)

- Selector expressions are not type-safe — string-based predicates can break silently

- Selector logic is separate from application code — harder to version and test together

- Complex selectors can impact broker performance at high message rates







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**Reference**: [Original Source](https://www.enterpriseintegrationpatterns.com/patterns/messaging/MessageSelector.html)