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⚙️ Backend-Specific Event Settings

Events often need fine-grained control over how they’re published—things like partitioning, headers, priorities, timestamps, etc. Dispytch supports this via the optional __backend_config__ class attribute on any EventBase subclass.

This lets you define backend-specific settings inside your event class in a clean, declarative way.

🧩 What Is __backend_config__?

__backend_config__ is an optional BaseModel that lets you pass custom options to your producer. Each backend (Kafka, RabbitMQ, etc.) can define its own config schema.

🔎 Example

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class UserCreated(EventBase):
    __topic__ = "user_events"
    __event_type__ = "user_created"
    __backend_config__ = KafkaEventConfig(partition_by="user.id")

    user: User
    timestamp: int

🪵 KafkaEventConfig

Use this config to control how events are sent to Kafka.

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class KafkaEventConfig(BaseModel):
    partition_by: Optional[str] = None
    partition: Optional[int] = None
    timestamp_ms: Optional[int] = None
    headers: Optional[dict] = None

🧠 partition_by: Dynamic Partitioning

Dispytch supports dot-notation to extract keys from deeply nested payloads and use them as Kafka partition keys.

✅ Example

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class SomeEvent(EventBase):
    __topic__ = "things"
    __event_type__ = "thing_happened"
    __backend_config__ = KafkaEventConfig(partition_by="user.id")

    user: User

If the event’s payload contains:

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{
    "user": {
        "id": "user123",
        "name": "Alice"
    },
    ...
}

Then user123 will be used as the partition key.

🐇 RabbitMQEventConfig

RabbitMQ gives you full control over message delivery via its rich AMQP options.

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class RabbitMQEventConfig(BaseModel):
    delivery_mode: int | None = None
    priority: int | None = None
    expiration: int | datetime | float | timedelta | None = None
    headers: dict | None = None
    content_type: str | None = None
    ...

Using this config, you can set AMQP-specific things

🔨 Implementing Custom Configs

If you're writing a custom producer (see Writing Custom Producers & Consumers), you can define your own config schema:

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class MyCustomConfig(BaseModel):
    foo: str
    retries: int = 3

Then inspect and apply it inside your send() method:

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if isinstance(config, MyCustomConfig):
    do_something_with(config.foo)