Java/Scala facade to datomic.client.api/api.async

This project contains thin Java and Scala facades to the Datomic Clojure Client api:

You can then use the various Datomic systems depending on the Client api from Java and Scala:

  • Peer Server
  • Dev local
  • Cloud

Using the facade in a live Cloud setting has not yet been tested. But since dev-local is equivalent and works fine, Cloud should too.


Most code is written in Scala but compiles to the same bytecode as Java.

Each language has been given its own exclusive namespace to ensure full compatibility and to accommodate for differences.

  • In the datomicJava namespace all interfaces take java-compatible types as input and return only java-compatible types.
  • In the datomicScala namespace most types are java-compatible but where collections are iterated for instance, a Scala collection type is returned.

Code organization

The implementation has largely followed the structure of the Datomic Java api.

Clojure functions of the Client api taking a Connection object are encapsulated in a Connection class and so on. We end up with 4 classes and their methods:

  • Datomic (similar to Peer)
    • clientCloud (providing AWSCredentialsProviderChain)
    • clientCloud (providing creds-profile name)
    • clientDevLocal
    • clientPeerServer
    • q
    • qseq
  • Client:
    • administerSystem
    • connect
    • createDatabase
    • deleteDatabase
    • listDatabases
  • Connection:
    • db
    • sync
    • transact
    • txRange
    • txRangeArray (convenience method for populated Array)
    • widh (convenience method for single invocation)
    • withDb
  • Db:
    • dbStats
    • asOf
    • since
    • with
    • history
    • datoms
    • indexRange
    • pull
    • indexPull

Various helper classes are added too.


Each language namespace has a sync and async package which corresponds to the two Datomic client api sync/async versions. All the above methods are implemented for each package.

Java async

The datomic client async api for Java generally returns a CompletableFutue of a custom Channel type.

Once the Future has completed, chunked results can be retrieved by calling chunk one or more times on the Channel object until the Clojure Channel is empty.

Each chunk is a custom Either type that can be either a Left projection with a CognitectAnomaly or a Right projection containing the successful result of a type T for the operation in question. That way, the result can be type checked for an anomaly or a success.

When the Clojure Channel is empty, Right(null) is returned. Consuming Java code might therefore want to check for such terminating null value (when needed).

Java sync

The datomic client sync api for Java returns the result as is (equivalent to the type T of the async api).

Cognitect anomalies are thrown as runtime exceptions.

Scala async

The datomic client async api for Scala returns a Future of a LazyList of chunks of data. The first (head) chunk of the LazyList is eargerly evaluated and subsequent chunks can be retrieved lazily by simply looping the LazyList.

Each chunk in the LazyList is an Either of either a Left[CognitectAnomaly] or a Right[T] where T is the main result type.

Scala sync

The datomic client sync api for Scala returns the result as is (equivalent to the type T of the async api).

Cognitect anomalies are thrown as runtime exceptions.


Clone this project and open in your IDE to explore.

git clone

This library presumes that you have a Datomic installation downloaded. It can be a free/starter/pro version, although the free version is a bit behind and won't provide all functionality. It's recommended to download an up-to-date version of starter/pro. On older versions of Datomic, some functionality might not be available. The qseq method was added in version 1.0.6165 for instance.

In one process, start a transactor:

cd <datomic-installation>
bin/transactor config/samples/

Then in another process (new tab in terminal) create a test database hello (if it has not already been created):

datomic % Peer.createDatabase("datomic:dev://localhost:4334/hello");

Peer-server in-mem

Running a peer-server in-mem doesn't require a transactor process to be running. So you can start the Peer Server directly from within the datomic installation directory:

bin/run -m datomic.peer-server -a k,s -d hello,datomic:mem://hello

To run the test suite you need to have a running transactor though!

Peer-server against transactor

To use a peer-server against a transactor, please start a transactor in one process, and the Peer Server in another process:

process 1:

bin/transactor config/samples/

process 2:

bin/run -m datomic.peer-server -h localhost -p 8998 -a k,s -d hello,datomic:dev://localhost:4334/hello

Dev-local / Cloud

To run tests against dev-local, please download the dev-tools and follow the instructions to install on your local machine.


Start a transactor in one process and an in-mem peer-server in another process.

Run the Java tests by right-clicking on the package in the project view (in IntelliJ) and choose Run -> Tests in 'client' (or run individual tests similarly).

Run the Scala tests by right-clicking on the test.scala.datomicScala.client package in the project view (in IntelliJ) and choose Run -> Specs2 in 'client' (or run individual tests similarly).

Run tests with sbt:


// Single test
sbt:datomic-client-api-java-scala> testOnly datomicScala.client.api.sync.DatomicTest

// Tests for Java
sbt:datomic-client-api-java-scala> testOnly datomicJava.client.api.*

// Tests for Scala 2.13 (default)
sbt:datomic-client-api-java-scala> testOnly datomicScala.client.api.*

// Tests for scala 2.12
sbt:datomic-client-api-java-scala> ++2.12.15; testOnly datomicJava.client.api.*
sbt:datomic-client-api-java-scala> ++2.12.15; testOnly datomicScala.client.api.*

Test caveats

Sometimes you'll need to re-start the peer-server to clear the cache. Then run the sbt tests twice to allow schema creation to propagate.

To run tests from IntelliJ, make sure that any previous sbt process of this project is not also running (kill it). Otherwise dev-local tests won't pass.

Use with your project

This library is available on Maven Central.

Add Java dependency in POM file:


<!-- If using dev-local -->

<!-- If using peer-server -->

Add Scala dependency in sbt build file (crosscompiles to Scala 2.12 and 2.13):

libraryDependencies ++= Seq(
  "org.scalamolecule" %% "datomic-client-api-java-scala" % "1.0.3",
  // If using dev-local
  "com.datomic" % "dev-local" % "1.0.238",
  // If using peer-server
  "com.datomic" % "datomic-pro" % "1.0.6344"

To use dev-local, please download from and install locally per included instructions and same for datomic pro.

Author / License

Marc Grue. Licensed under the Apache License 2.0.