datahike-postgres

Datahike with Postgres as data storage.

Prerequisites

For datahike-postgres you will need to know the configuration of a running Postgres server as well as the name of an existing Postgres user.

On Ubuntu, there are at least two ways to prepare a Postgres server for datahike:

1. The easy way: Use a docker image
2. Install and prepare Postgres on your native system

For installation instructions see below.

Usage

Add to your leiningen dependencies:

After including the datahike API and the datahike-postgres namespace, you can use the Postgres backend now using the keyword :pg

(ns project.core
  (:require [datahike.api :as d]
            [datahike-postgres.core]))

;; Create a config map with postgres as storage medium
(def config {:backend :pg
             :host "localhost"
             :port 5432
             :username "alice"
             :password "foo"
             :path "/example-db"})

;; Alternatively, use an URI as configuration
;; (def config "datahike:pg://alice:foo@localhost:5432/example-db")

;; Create a database at this place, by default configuration we have a strict
;; schema and temporal index
(d/create-database config)

(def conn (d/connect config))

;; The first transaction will be the schema we are using:
(d/transact conn [{:db/ident :name
                   :db/valueType :db.type/string
                   :db/cardinality :db.cardinality/one }
                  {:db/ident :age
                   :db/valueType :db.type/long
                   :db/cardinality :db.cardinality/one }])

;; Let's add some data and wait for the transaction
(d/transact conn [{:name  "Alice", :age   20 }
                  {:name  "Bob", :age   30 }
                  {:name  "Charlie", :age   40 }
                  {:age 15 }])

;; Search the data
(d/q '[:find ?e ?n ?a
       :where
       [?e :name ?n]
       [?e :age ?a]]
  @conn)
;; => #{[3 "Alice" 20] [4 "Bob" 30] [5 "Charlie" 40]}

;; Clean up the database if it is not needed any more
(d/delete-database config)

Postgres via Docker image

Install Docker

sudo apt install docker-engine

Alternatively, you can get the latest version using the instructions here.

Pull the docker image

sudo docker pull postgres

Configure the server

sudo docker run --name test-pg -p <PORT>:5432 -e POSTGRES_PASSWORD=<PASSWORD> -e POSTGRES_USER=<USER> -e POSTGRES_DB=<DATABASENAME> -d postgres

Native Postgres Installation and Configuration

In order to use Postgres as backend, you need a current Postgres installation on your target system. See the Postgres website for installation instructions for any target system.

For Ubuntu, you can simply use the package manager:

sudo apt install postgresql

Controlling the server

The Postgres server on Ubuntu is controlled with commands like the following:

sudo service postgresql start
sudo service postgresql stop

Check or Change Port

Port 5432 is the default port for Postgres.

To be sure which port is being used, you can try the following command:

sudo netstat -plunt |grep postgres
# => tcp 0 0 127.0.0.1:<PORT> 0.0.0.0:* LISTEN 1235/postgres

You can change the port by editing the configuration file, found with

locate postgresql.conf
# => something like /etc/postgresql/10/main/postgresql.conf

After the editing, you will have to restart the server:

sudo service postgresql restart

Create User

A user without a password should suffice:

sudo -u postgres createuser <USER>

For adding a password, do

sudo -u postgres psql

And then, on the psql prompt

alter user <USER> with encrypted password '<PASSWORD>';

Run tests

For the tests to be working, you need to

• use port 5432
• create a user named alice
• with password foo

If you have Docker installed on Ubuntu, you can simply do:

sudo docker run --name test-pg -p 5432:5432 -e POSTGRES_PASSWORD=foo -e POSTGRES_USER=alice -e POSTGRES_DB=config-test -d postgres

Otherwise, follow the instructions above to configure your server correctly.

License

Copyright © 2019 lambdaforge UG (haftungsbeschränkt)

This program and the accompanying materials are made available under the terms of the Eclipse Public License 1.0.