deptracpy

Core concepts

At the heart of DepTracPy are three main concepts:

• Layers are groups of files that you define
• Rulesets describe which layers a layer can communicate with
• Violations show when a layer uses files from another layer that is forbidden by the currently configured rulesets.

Layers

DepTracPy allows you to group different tokens(files) into layers. Technically layers are nothing more than a collection of those tokens.

Each layer has a unique name and a list of one or more collectors, which will look for tokens should be assigned to this layer.

If you want to ensure your application follows the MVC architecture pattern then you can create a config file that makes sure a View does not directly interact with a Controller or that Models are independent of both Views and Controllers.

DepTracPy allows you to visualize and enforce a ruleset based on such layer information.

By default, all dependencies between layers are forbidden!

Collecting Layers

If your application has Controllers and Models, DepTracPy allows you to group them into layers.

paths:
  - src

layers:
  - name: Models
    collectors:
      - type: ModuleRecursive
        path: 'myapp.Models'
  - name: Controllers
    collectors:
      - type: ModuleRecursive
        path: 'myapp.Controllers'
ruleset: [ ]

At first, lets take a closer look at the first layer (named Models).

Here we decided that our software has some kind of layer called Models. You assign tokens to this layer with the help of Collectors.

Collectors are responsible for taking a closer look at your code and decide if a token is part of a layer. By using the ModuleRecursive collector you can define a module prefix. File in that module and its submodules becomes part of the assigned layer. In this example we define that every file in the myapp.Models module will be a part of the Model layer.

Every file matching myapp.Controllers module will become a part of the Controller layer.

As we defined our layers, we can generate a dependency graph for the example configuration: (Make sure Graphviz (dot) is installed on your system)

deptracpy --formatter=dot

Rulesets

Allowed dependencies between layers are configured in a ruleset.

By default, DepTracPy will raise a violation for every dependency between layers. In real software you want to allow dependencies between different kinds of layers.

As a lot of architectures define some kind of controllers, services and repositories, a natural approach for this would be to define these rules:

• Controllers may access services, but not repositories.
• Services may access repositories, but not controllers.
• Repositories neither may access services nor controllers.

We can define this using the following configuration:

# deptracpy.yaml
paths:
  - src

layers:
  - name: Controllers
    collectors:
      - type: ModuleRecursive
        path: 'myapp.Controller'
  - name: Service
    collectors:
      - type: ModuleRecursive
        path: 'myapp.Service'
  - name: Repository
    collectors:
      - type: ModuleRecursive
        path: 'myapp.Repository'
ruleset:
  Controller:
    - Service
  Service:
    - Repository
  Repository: ~

Take a closer look at the ruleset. We allow the Controller layer to access Service and Service can access Repository, but Repository may not access any of the two other layers.

Different Layers and Different Views

In the example above we defined 3 different layers (controller, repository and service). DepTracPy gives architects the power to define what kind of layers exist.

Typical use cases are:

• caring about layers in different architectures (tier, hexagonal, ddd, …)
• caring about dependencies between different kinds of services (infrastructure services / domain services / entities / DTOs / …)
• caring about coupling to third party code like composer vendors, frameworks, …
• enforcing naming conventions
• …

Typically, software has more than just one view. It is possible to use multiple config files, to take care about different architectural views.

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