Datomic Setup

October 25, 2021

👋 Hello there!!

Today we’ll be walking through how to set up the database library Datomic for use in Leiningen project. I’ve had a lot of issues and learned a lot so hopefully this will serve helpful for someone else or me in the future.

Installing Datomic

In the datomic doc they mention to install the datomic library into your local maven directory. I didn’t know I had a local maven directory, so I looked around the ~/.m2 and tried running the install script that came from the install zip file, but that didn’t work when trying to import datomic to the project.

Once you request an install from their website they sent through my email a password and username that I had not idea what for. As I’ve read more the key concept that made me “aha” was that datomic was not in any public maven repository. In order to download and use the library I would have to access a private repository to download the library.

But how do we setup Leiningen to be able to access the private repository.

Leiningen Setup

Leiningen project.clj has a property to define what repositories to look for listed dependencies in its projects. But knowing the private repository wasn’t enough how do we pass in some of our secrets (username/password) without committing them into code?

Using environment based variables

...
  :repositories [["cognitect-dev-tools"
                  {:url      "https://dev-tools.cognitect.com/maven/releases/"
                   :username :env
                   :password :env}]]

We export the secrets in our shell or our .bashrc| .zhrc like so

export LEIN_USERNAME=xxxxx
export LEIN_PASSWORD=xxxxxxxxxxxxxxxxxx

We add our datomic to deps

  :dependencies [...
                 [com.datomic/dev-local "1.0.238"]]

Once we run our leiningen project our project install the dependencies properly 🎉!

Setup local Database

So after getting it installed we need just one more step to set up our local database. We need to specify our directory path of our databases.

In our ~/.datomic/dev-local.edn we specify the above directory

{:storage-dir "/Users/ecarreras/tic-tac-toe-web/db"}

Once we have this we can use our local instance of Datomic!

Using a sample data and copying it to our above directory

(ns tic-tac-toe-server.datomic-persistence
  (:require [datomic.client.api :as d]))

(def client (d/client {:server-type :dev-local
                       :system "datomic-samples"}))

(d/list-databases client {})
;=> ["mbrainz-subset" "solar-system" "social-news" "movies" ...]

Next we’ll be looking to create a new implementation of perishable using datomic and adding a new feature to our tic-tac-toe game, leaderboards!

❤️

Written by Edgardo Carreras.

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