FastAPI Configuration Recipe

This recipe is a starting point for a layered FastAPI project. It is regular Deply configuration, not a built-in preset. Adapt the source directories and rules to the architecture the project actually uses.

Verified Template Recipe

For the official template, use the zero-violation Full Stack FastAPI Template recipe.

The example assumes this structure:

src/app/
├── domain/
├── application/
├── infrastructure/
└── interface/
    └── routers/

Complete Configuration

deply:
  paths:
    - "."

  exclude_files:
    - '.*/\.venv/.*'
    - '.*/tests?/.*'
    - '.*/migrations/.*'

  layers:
    - name: domain
      collectors:
        - type: directory
          directories:
            - "src/app/domain"

    - name: application
      collectors:
        - type: directory
          directories:
            - "src/app/application"

    - name: infrastructure
      collectors:
        - type: directory
          directories:
            - "src/app/infrastructure"

    - name: interface
      collectors:
        - type: bool
          any_of:
            - type: file_regex
              regex: '.*/routers?/.*\.py$'
            - type: decorator_usage
              decorator_regex: '.*\.(get|post|put|patch|delete)'

  ruleset:
    domain:
      disallow_layer_dependencies:
        - application
        - infrastructure
        - interface
      disallow_external_imports:
        - fastapi
        - starlette
        - pydantic
        - sqlalchemy
        - requests

    application:
      disallow_layer_dependencies:
        - infrastructure
        - interface

Validate and run the configuration from the project root:

deply validate --config=deply.yaml
deply analyze --parallel --config=deply.yaml

Route Layout Variants

For projects that keep routes in modules such as api/routes.py or api/v1/users.py, replace the interface file collector with a pattern that matches the actual layout:

- type: file_regex
  regex: '.*/api/.*\.py$|.*/routes?\.py$'

Decorator collection is useful when route handlers are not kept in dedicated modules:

- type: decorator_usage
  decorator_regex: '.*\.(get|post|put|patch|delete|options|head)'

Pydantic Domain Models

The complete recipe blocks pydantic in domain to keep transport DTOs outside business logic. If Pydantic models are an intentional part of the domain model, remove only pydantic from disallow_external_imports.

Do not remove fastapi or starlette unless the domain intentionally owns HTTP concerns.

SQLAlchemy Persistence

When SQLAlchemy models live outside the generic infrastructure directory, add a persistence collector:

- name: infrastructure
  collectors:
    - type: bool
      any_of:
        - type: directory
          directories:
            - "src/app/infrastructure"
        - type: file_regex
          regex: '.*/models\.py$|.*/models/.*\.py$'
        - type: class_inherits
          base_class: "sqlalchemy.orm.DeclarativeBase"

If SQLAlchemy models are intentionally used as domain entities, remove sqlalchemy from the domain import restriction instead of suppressing each violation.

Full Stack FastAPI Template