Production Database - Heroku Postgres

Heroku Postgres

Heroku provides a on-demand PostgreSQL service with very good support tooling. The Hobby plan is free to use with a free Heroku account (no credit card needed).

PostgreSQL provides a production grade relational database with support for JSON an other common data types. As its such a feature rich database

PostgreSQL instance runs outside the application code (unlike H2 database).

Provision a database

Login to Heroku using your free account.

Two Heroku apps have already been created for the banking on Clojure project pipeline, staging and live, so a database should be provisioned for both apps.

Clojure WebApps - Deployment - Heroku Pipeline for Banking on Clojure

Select the staging app from the pipeline dashboard.

Clojure WebApps - Deployment - Heroku Pipline for Banking on Clojure - details

In the Overview section, click Configure Add-ons

Clojure WebApps - Deployment - Heroku Pipline for Banking on Clojure - staging app overview

Start typing Postgres in the Add-ons text box to see the matching add-ons available. Select Heroku Postgres.

Clojure WebApps - Deployment - Heroku Pipline for Banking on Clojure - staging app addon Heroku Postgres

Select the Hobby plan in the pop-up window. The Hobby plan is free and limited to 10,000 rows. The plan can be upgraded ones the app starts making money (or funding is raised).

Clojure WebApps - Deployment - Heroku Pipline for Banking on Clojure - staging app addon Heroku Postgres plan

The Postgres database is immediately provisioned and available for use.

Clojure WebApps - Deployment - Heroku Pipline for Banking on Clojure - staging app addon Heroku Postgres provisioned

Database Configuration on Heroku

Provisioning an Heroku postgres database adds a DATABASE_URL Config Var (Heroku Environment Variable) to the application the database is attached to.

In the Heroku dashboard, view the Settings and select Show Config Vars

Clojure WebApps - Deployment - Heroku Pipline for Banking on Clojure - staging app addon Heroku Postgres Config Vars

Click on the pencil icon to see the full connection string, which takes the following form:

postgres://username:password@host:port/database-name

This is not a correct JDBC connection string, but it can be used to generate one.

Generate the JDBC connection

Use the Heroku CLI tool to get the JDBC connection string for the database.

For the Banking on Clojure app, the following

heroku run echo \$JDBC_DATABASE_URL --app banking-on-clojure-staging

This returns the correct JDBC connection string in the form:

jdbc:postgresql://<hostname>:port/<database-name>?user=<username>&password=<password>&sslmode=require

This jdbc connection string is generated from the DATABASE_URL config var that is added to the heroku app when a database is provisioned.

There are several applications attached to the Git repository, so its required to specify which application to run. The run command runs a container for the app, a Linux system that has the database attached. Once the echo command is complete the container is shut down and discarded automatically.

Viewing the database details on Heroku dashboard

This will switch over to the data.heroku.com website, so you may be prompted to login again.

Clojure WebApps - Databases - Heroku Postgres staging database

Adding Postgresql driver to Clojure project

Add the latest postgresql jdbc driver to the deps.edn file in the bankking on clojure project

 :deps
 {org.clojure/clojure {:mvn/version "1.10.1"}

  ;; Web Application
  http-kit        {:mvn/version "2.3.0"}
  ring/ring-core  {:mvn/version "1.8.1"}
  ring/ring-devel {:mvn/version "1.8.1"}
  compojure       {:mvn/version "1.6.1"}
  hiccup          {:mvn/version "2.0.0-alpha2"}

  ;; Database
  seancorfield/next.jdbc    {:mvn/version "1.1.569"}
  com.h2database/h2         {:mvn/version "1.4.200"}
  org.postgresql/postgresql {:mvn/version "42.2.16"}}

The Postgresql jdbc driver library will be used by next.jdbc

Creating a staging data source

Add a JDBC_DATABASE_URL environment variable to hold the JDBC connection string to the Heroku database

(def data-source-postgresql
    (jdbc/get-datasource (System/getenv "JDBC_DATABASE_URL")) )

Now the same SQL queries created for the H2 database can be tested on with PostgreSQL.

Testing queries with PostgreSQL

In practice is seems there are noticeable differences between H2 and PostgreSQL, especially in terms of schema definitions.

For example, to create a table the table namespace should be supplied, in this case public. The table creation syntax also as an IF clause, so if the database table already exists then the SQL statement does not try to create it and cause an error.

(jdbc/execute!
    data-source-postgresql
    ["CREATE TABLE IF NOT EXISTS public.account_holder (
      user_id serial PRIMARY KEY,
      username VARCHAR ( 50 ) UNIQUE NOT NULL,
      password VARCHAR ( 50 ) NOT NULL,
      email VARCHAR ( 255 ) UNIQUE NOT NULL,
      created_on TIMESTAMP NOT NULL,
      last_login TIMESTAMP"])

The PostgreSQL syntax for creating tables is:

  CREATE TABLE [IF NOT EXISTS] table_name (
  column1 datatype(length) column_contraint,
  column2 datatype(length) column_contraint,
  column3 datatype(length) column_contraint,
  table_constraints);

Use DBeaver to generate SQL

DBeaver is a free and comprehensive database tool that will generate SQL statements from database designs.

Resources

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