Attrs Request/Response¶

Advanced features - Uses the attrs library for more features than standard dataclasses.

Best For¶

More features than standard dataclasses
Functional-style codebases
When you need more control than dataclasses
Complex validation scenarios

Installation

pip install attrs

Usage¶

import cqrs
import attrs
from typing import Self

@attrs.define
class AttrsRequest(cqrs.IRequest):
    """Request using attrs."""
    user_id: str = attrs.field(validator=attrs.validators.instance_of(str))
    action: str = attrs.field(validator=attrs.validators.instance_of(str))

    def to_dict(self) -> dict:
        """Convert to dictionary."""
        return attrs.asdict(self)

    @classmethod
    def from_dict(cls, **kwargs) -> Self:
        """Create from dictionary."""
        return cls(**kwargs)

@attrs.define(frozen=True)
class AttrsResponse(cqrs.IResponse):
    """Immutable response using attrs."""
    result: str = attrs.field()
    status: str = attrs.field()

    def to_dict(self) -> dict:
        """Convert to dictionary."""
        return attrs.asdict(self)

    @classmethod
    def from_dict(cls, **kwargs) -> Self:
        """Create from dictionary."""
        return cls(**kwargs)

class AttrsHandler(cqrs.RequestHandler[AttrsRequest, AttrsResponse]):
    @property
    def events(self) -> list[cqrs.IEvent]:
        return []

    async def handle(self, request: AttrsRequest) -> AttrsResponse:
        return AttrsResponse(
            result=f"Processed {request.action}",
            status="success"
        )

Validation¶

Attrs provides powerful validation capabilities:

import attrs
from typing import Self

@attrs.define
class ValidatedRequest(cqrs.IRequest):
    email: str = attrs.field(
        validator=attrs.validators.matches_re(r'^[\w\.-]+@[\w\.-]+\.\w+$')
    )
    age: int = attrs.field(
        validator=attrs.validators.and_(
            attrs.validators.ge(0),
            attrs.validators.le(120)
        )
    )

    def to_dict(self) -> dict:
        return attrs.asdict(self)

    @classmethod
    def from_dict(cls, **kwargs) -> Self:
        return cls(**kwargs)

Custom Converters¶

You can use converters for automatic type conversion:

@attrs.define
class ConvertedRequest(cqrs.IRequest):
    count: int = attrs.field(converter=int)
    tags: list[str] = attrs.field(
        converter=lambda x: x.split(",") if isinstance(x, str) else x
    )

    def to_dict(self) -> dict:
        return attrs.asdict(self)

    @classmethod
    def from_dict(cls, **kwargs) -> Self:
        return cls(**kwargs)

Factory Functions¶

Attrs supports factory functions for default values:

@attrs.define
class RequestWithDefaults(cqrs.IRequest):
    user_id: str
    metadata: dict = attrs.field(factory=dict)
    tags: list[str] = attrs.field(factory=list)

    def to_dict(self) -> dict:
        return attrs.asdict(self)

    @classmethod
    def from_dict(cls, **kwargs) -> Self:
        return cls(**kwargs)

Immutable Classes¶

Use frozen=True for immutability:

@attrs.define(frozen=True)
class ImmutableRequest(cqrs.IRequest):
    user_id: str
    action: str

    def to_dict(self) -> dict:
        return attrs.asdict(self)

    @classmethod
    def from_dict(cls, **kwargs) -> Self:
        return cls(**kwargs)