Day in the Life CRM

This code base is used in a talk outlining ADTs and Typeclasses.

Getting started

Install Java 8, for example from Oracle.

Install the sbt build tool for Scala as described in the reference manual.

Then run the following from your terminal/shell:

sbt run

This will start the project on http://localhost:8080/

First time you run it, libraries will be downloaded from the internet....

Example API calls

These examples use HTTPie to call the server:

• List all customers: http :8080/customers (with cURL this would be curl http://localhost:8080/customers)

• List a customer: http :8080/customers/2

• Add a customer: http POST :8080/customers name=Connie phone='+1 555 9876'

• Update a customer: http PATCH :8080/customers/2 phone="+44 555 555" name="Robert"

Code

• api.scala defines the REST endpoints.
• database.scala defines all the queries and establishes an in-memory database.
• model.scala gives the data model.
• main.scala pulls everything together into a web server.

Also:

• type-class.scala contains the code used in the presentation for building up the idea of a type class.

Libraries and Concepts

This code base makes use of:

• circe to encode and decode JSON text into case classes.
• doobie for database access.
• http4s as a web server.

It makes use of the types Stream and Task, which are concurrency concepts. These are from the fs2 project. For example, Task describes an effect. The effect isn't performed until one of the unsafeRun methods is called. The http4s web server expects Task to be used, and arranges for them to be run on an appropriate thread pool.

Credit

This is in part a mash-up of parts from Typelevel todomvc, http4s todomvc, and Bulletin