Dependency injection example with system

Definition

This is a case study project for the system library, summing up practices that have emerged in the Clojure landscape.

It demonstrates the following:

• How dependency injection works with the component library.
• How Ring handlers are being closed over to expose dependencies such as the database.
• How the Duct-style abstractions clearly and cleanly delineate endpoints, middleware and handler.
• How components are extended to provide application-level functionality.

Mission statement

Names are important. What names? Those behind our favorite movies, that’s who! So let’s save them via a web service.

Installation

In our development environment, we use a in-memory database and a web server listening on port 3025.

$ boot dev

Or, if you don’t intend to connect with a REPL to the running system, type simply:

$ boot dev-run

In our production environment, we use a persistent database and a web server listening on port 8008.

$ boot prod-run

Usage

To search for a movie’s director:

curl -H "Content-Type: application/edn" -X POST -d '{:movie "Realm of the Senses"}' http://localhost:3025/movie 

{:director ("Nagisa Ōshima")}

To add a director to our database:

curl -H "Content-Type: application/edn" -X PUT -d '{:director "Nagisa Ōshima"}' http://localhost:3025/director

To list directors in our database:

curl http://localhost:3025/directors

("Nagisa Ōshima")

Let’s look for another all-time favorite.

curl -H "Content-Type: application/edn" -X POST -d '{:movie "Professione: reporter"}' http://localhost:3025/movie 

{:director ("Michelangelo Antonioni")}

Now that we know the name of the director, we can persist it to our database.

curl -H "Content-Type: application/edn" -X PUT -d '{:director "Michelangelo Antonioni"}' http://localhost:3025/director

Let’s verify it’s there:

curl http://localhost:3025/directors

("Nagisa Ōshima" "Michelangelo Antonioni")

Let’s repeat this one more time for a third movie/director:

curl -H "Content-Type: application/edn" -X POST -d '{:movie " À bout de souffle"}' http://localhost:3025/movie 

{:director ("Jean-Luc Godard")}

Saving to database:

curl -H "Content-Type: application/edn" -X PUT -d '{:director "Jean-Luc Godard"}' http://localhost:3025/director

We should now have three directors in our database:

curl http://localhost:3025/directors

("Nagisa Ōshima" "Michelangelo Antonioni" "Jean-Luc Godard")

Let’s suppose we want to remove one.

curl -H "Content-Type: application/edn" -X DELETE -d '{:director "Nagisa Ōshima"}' http://localhost:3025/director

Let’s verify the removal was properly executed.

curl http://localhost:3025/directors

("Michelangelo Antonioni" "Jean-Luc Godard")

License

Distributed under the Eclipse Public License, the same as Clojure.