OpenAPI Generator for Elixir

A highly-configurable code generator that combines ergonomics with maintainability.

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OpenAPI is a standard way to describe REST APIs on the web. Anyone can create an OpenAPI description document that includes the available endpoints, expected request data, and possible responses. For example, GitHub maintains a comprehensive OpenAPI description for their services.

Generating code from an OpenAPI description can be relatively easy — this project certainly isn't the first — but there's a catch: API descriptions often don't translate into ergonomic code. Most users of an API client library don't want to think about the difference between a NullableRepository and Repository, as in the OpenAPI 3.0 GitHub API description. (They have the same fields, but one has nullable: true.) Users just want to get back a %Repository{} or nil.

The goal of this library is to create ergonomic client libraries from OpenAPI descriptions. At the same time, the changes made to the code are easily repeatable (fully automated) for the sake of maintainability. Think: the friendliness of your favorite hand-crafted client library applied to the scale of large APIs.

See an example client library here.

For more on how this is accomplished, see Configuration below and the configuration guide.

Installation

This library is available on Hex.pm. Add the dependency in mix.exs:

def deps do
  [
    {:oapi_generator, "~> 0.1.0", only: :dev, runtime: false}
  ]
end

Then install the dependency using mix deps.get. Most libraries only need access to the mix api.gen task in a development environment. If your use case requires calling the generator in production or testing, be sure to modify or remove only: :dev and runtime: false as appropriate.

Configuration

The real power of this library is in the available configuration. Although the options are conceptually simple, they add up to a better user experience.

This project uses configuration profiles to allow multiple configurations with the same package. To get started, create a profile called default in your configuration file:

# config/config.exs

import Config

config :oapi_generator, default: [
  output: [
    base_module: Example,
    location: "lib/example"
  ]
]

This is the minimum viable configuration for most client libraries. It will create modules namespaced with Example. and save files in lib/example.

Some the options supported by the generator out-of-the-box include:

• Ignoring schemas and operations
• Renaming schemas
• Grouping schemas into module namespaces
• Merging schemas to create a struct with multiple typespecs
• Writing schemas and operation modules to different locations
• Introducing additional schema fields
• Adding custom use statements to generated modules
• Overriding function return types

For more information, see the configuration guide.

Plugins

If the available configuration isn't enough, client library authors can also reimplement portions of the code generator using plugins. Most of the crucial parts of the processing and rendering of code are implemented as default callbacks for a behaviour. These can be overridden for additional flexibility. See the plugins guide for additional information.

Usage

Once the library is installed and configured, use mix api.gen with the name of the configuration profile and the OpenAPI description file(s):

mix api.gen default path/to/rest-api-description/spec.yaml

Further Reading

• Code of Conduct
• Contribution Guidelines
• License
• OpenAPI Specification

Sponsorship

If you like this library or it makes you money, please consider sponsoring.