todo-backend-pedestal

An implementation of the Todo Backend spec using Pedestal and Datomic.

One-time Setup

1. Clone https://github.com/TodoBackend/todo-backend-js-spec.git locally
2. Run a Datomic transactor
3. Install the Datomic schema: lein run -m install-schema _datomic_uri_

See it work

1. Start the application: lein run-dev *
2. Open the specs to see test results.
3. Enter localhost:8080 as the base URL

* lein run-dev automatically detects code changes. Alternatively, you can run in production mode with lein run.

Configuration

To configure logging see config/logback.xml. By default, the app logs to stdout and logs/. To learn more about configuring Logback, read its documentation.

How to get to Here

This project started from the pedestal-service leiningen template:

lein new pedestal-service todo-backend-pedestal

I updated project.clj to bump the Clojure dependency up to 1.7.0-RC2 (the current revision when I started this.) I also added Datomic Free as a dependency. The start-transactor.sh script is something I carry from one project to the next because I have a bad memory for options.

The next thing I did was start working on the Pedestal routes. I wanted to get the first of the Todo Backend tests to pass. To get going, I started a REPL:

lein repl

Then I connected to it from CIDER (I'm an Emacs user.) Once I had a prompt, I started a dev server so I could edit routes and reload the file:

todo-backend.server=> (def srv (run-dev))

Creating your [DEV] server...
#'todo-backend.server/srv

At that point, I could hit http://localhost:8080/ and see the template's default "Hello, World!" page.

I like to have my plumbing in place, so the next thing I added is the insert-datomic interceptor. That attaches a Datomic connection to every request, along with the value of the DB that is current when the request begins. It's really handy to have that on the request, so every piece of logic uses a consistent basis.

Next, it's a matter of creating routes and translating data. todo-backend-js-spec uses JSON for transport, so we have a bit of conversion to do in the handlers.

For the most part, we can use Pedestal interceptors. We use body-params/body-params. It modifies the request map by deserializing JSON into ordinary Clojure maps, then attaching that as :json-params on the request. From there, we can translate JSON maps into datoms to update Datomic. On the way back to the client, we replace the keys for Datomic attributes with keywords. The bootstrap/json-body interceptor serializes the data structure into JSON as the response is generated.

Links

• Other examples