Datomic Peer (free), persisted

Minimal project setup to persist data to disk with Molecule and a free Datomic Peer database (protocol: free).

import sbt.Keys._

lazy val demo = project.in(file("."))
  .settings(name := "molecule-datomic-peer-free-free")

lazy val app = project.in(file("app"))
    scalaVersion := "2.13.5",
    resolvers ++= Seq(
      "clojars" at "https://clojars.org/repo",

    libraryDependencies ++= Seq(
      "org.scalamolecule" %% "molecule" % "0.25.1",
      "com.datomic" % "datomic-free" % "0.9.5697"

    // path to domain model directory
    moleculeDataModelPaths := Seq("app"),

    // Generate Molecule boilerplate code with `sbt clean compile -Dmolecule=true`
    moleculePluginActive := sys.props.get("molecule") == Some("true"),

    // Let IDE detect created jars in unmanaged lib directory
    exportJars := true

1. Start transactor

First, you need to start a Datomic transactor in its own process:

cd <your-datomic-free-distribution>
bin/transactor config/samples/free-transactor-template.properties

Note that although the Peer in your application code in this project setup is the free version of Peer, the transactor can be of any type - a free or a starter/pro. As long as your application code can reach it via a matching host:port it will work. A datomic database is in other words interchangeable between free/pro.

2. Connect to Peer

Then connect to the database:

implicit val conn = Datomic_Peer.connect("localhost:4334/sampledb", "free")

Or, if we want to test a clean database each time, we could recreate the database and transact the schema on each run:

implicit val conn = Datomic_Peer.recreateDbFrom(SampleSchema, "localhost:4334/sampledb", "free")

In this setup we use the “free” protocol which is intended for development databases that are persisted on local disk. See other storage options for alternative storage options.

3. Make molecules

Having an implicit connection in scope, we can start transacting and querying sampledb with molecules:

// Transact

// Query
assert(Person.name.age.get.head == ("John", 24))

Add/change definitions in the SampleDataModel and run sbt clean compile -Dmolecule=true in your project root to have Molecule re-generate boilerplate code. Then you can try out using your new attributes in new molecules in SampleApp.