Build an Elixir application that uses YSQL

The following tutorial shows a small Elixir application that connects to a YugabyteDB cluster using the Elixir Postgrex driver and performs basic SQL operations. Use the application as a template to get started with YugabyteDB Aeon in Elixir.

Prerequisites

The latest versions of Elixir, Erlang VM, IEx and Mix (tested with Elixir 1.17.1 and Erlang/OTP 26 erts-14.2.5).

Clone the application from GitHub

Clone the sample application to your computer:

git clone https://github.com/YugabyteDB-Samples/yugabytedb-simple-elixir-app.git && cd yugabytedb-simple-elixir-app/postgrex/simple_app

Provide connection parameters

If your cluster is running on YugabyteDB Aeon, you need to modify the connection parameters so that the application can establish a connection to the YugabyteDB cluster. (You can skip this step if your cluster is running locally and listening on 127.0.0.1:5433.)

To do this:

1. Open the lib/simple_app.ex file.

2. Set the following configuration parameter constants:

   • hostname - the host name of your YugabyteDB cluster. For local clusters, use the default (127.0.0.1). For YugabyteDB Aeon, select your cluster on the Clusters page, and click Settings. The host is displayed under Connection Parameters.
   • port - the port number for the driver to use (the default YugabyteDB YSQL port is 5433).
   • database - the name of the database you are connecting to (the default is yugabyte).
   • username and password - the username and password for the YugabyteDB database. For local clusters, use the defaults (yugabyte and yugabyte). For YugabyteDB Aeon, use the credentials in the credentials file you downloaded.
   • ssl: [cacertfile:...] - the full path to the YugabyteDB Aeon cluster CA certificate. For local clusters, skip or remove this parameter.

3. Save the file.

Build and run the application

First, add all required dependencies.

mix deps.get

Compile the application and start an IEx session:

iex -S mix

Start the application.

SimpleApp.start

You should see output similar to the following:

>>>> Successfully connected to YugabyteDB! PID: #PID<0.221.0>
>>>> Successfully created table DemoAccount.
>>>> Selecting accounts:
["Jessica", 28, "USA", 10000]
["John", 28, "Canada", 9000]
>>>> Transferred 800 between accounts.
>>>> Selecting accounts:
["Jessica", 28, "USA", 9200]
["John", 28, "Canada", 9800]
:ok

You have successfully executed a basic Elixir application that works with YugabyteDB.

Explore the application logic

Open the simple_app.ex file in the yugabytedb-simple-elixir-app/postgrex/simple_app/lib folder to review the methods.

start

The start method establishes a connection with your cluster via the Elixir Postgrex driver and executes the rest of the application logic.

db_config = @db_config
{:ok, pid} = Postgrex.start_link(db_config)

create_database

The create_database method creates a sample table and loads it with a few records.

Postgrex.query!(pid, "DROP TABLE IF EXISTS DemoAccount", [])

Postgrex.query!(pid, """
CREATE TABLE DemoAccount (
    id int PRIMARY KEY,
    name varchar,
    age int,
    country varchar,
    balance int)
""",[])

Postgrex.query!(pid, """
INSERT INTO DemoAccount VALUES
    (1, 'Jessica', 28, 'USA', 10000),
    (2, 'John', 28, 'Canada', 9000)
""",[])

select_accounts

The select_accounts method queries the data from the database.

result = Postgrex.query!(pid,
    "SELECT name, age, country, balance FROM DemoAccount", [])

Enum.each(result.rows, fn row ->
    IO.inspect(row)
end)

transfer_money

The transfer_money method updates your data consistently with distributed transactions.

Postgrex.transaction(pid, fn(conn) ->
    # Deduct amount from Jessica's account
    Postgrex.query!(conn,
    "UPDATE DemoAccount SET balance = balance - $1 WHERE name = 'Jessica'", [amount])

    # Add amount to John's account
    Postgrex.query!(conn,
    "UPDATE DemoAccount SET balance = balance + $1 WHERE name = 'John'", [amount])
end)

Learn more

YugabyteDB Community Open Hours - featuring Chris McCord, the creator of the Phoenix framework, demonstrating how to build multi-region applications using Phoenix, Fly.io, and YugabyteDB.