Connect from Elixir with Ecto to Neon

This guide describes how to connect from an Elixir application with Ecto, which is a database wrapper and query generator for Elixir. Ecto provides an API and abstractions for interacting databases, enabling Elixir developers to query any database using similar constructs.

The instructions in this guide follow the steps outlined in the Ecto Getting Started guide, modified to demonstrate connecting to a Neon Serverless Postgres database. It is assumed that you have a working installation of Elixir.

To connect to Neon from Elixir with Ecto:

1. Create a database in Neon and copy the connection string
2. Create an Elixir project
3. Add Ecto and Postgrex to the application
4. Configure Ecto
5. Create a migration and add a table
6. Next steps

Create a database in Neon and copy the connection string

The instructions in this configuration use a database named friends.

To create the database:

1. Navigate to the Neon Console.
2. Select a project.
3. Select Databases.
4. Select the branch where you want to create the database.
5. Click New Database.
6. Enter a database name (friends), and select a database owner.
7. Click Create.

You can obtain the connection string for the database from the Connection Details widget on the Neon Dashboard. Select a branch, a role, and the database you want to connect to. A connection string is constructed for you. Your connection string should look something like this:

postgresql://alex:AbC123dEf@ep-cool-darkness-123456.us-west-2.aws.neon.tech/friends

You will need the connection string details later in the setup.

Create an Elixir project

Create an Elixir application called friends.

mix new friends --sup

The --sup option ensures that the application has a supervision tree, which is required by Ecto.

Add Ecto and Postgrex to the application

1. Add the Ecto and the Postgrex driver dependencies to the mix.exs file by updating the deps definition in the file to include those items. For example:

   defp deps do
     [
       {:ecto_sql, "~> 3.0"},
       {:postgrex, ">= 0.18.0"}
     ]
   end

   Ecto provides the common querying API. The Postgrex driver acts as a bridge between Ecto and Postgres. Ecto interfaces with its own Ecto.Adapters.Postgres module, which communicates to Postgres through the Postgrex driver.

2. Install the Ecto and the Postgrex driver dependencies by running the following command in your application directory:

   mix deps.get

Configure Ecto

Run the following command in your application directory to generate the configuration required to connect from Ecto to your Neon database.

mix ecto.gen.repo -r Friends.Repo

Follow these steps to complete the configuration:

1. The first part of the configuration generated by the mix ecto.gen.repo command is found in the config/config.exs file. Update this configuration with your Neon database connection details. Use the connection details from the Neon connection string you copied in the first part of the guide. Your hostname will differ from the example below.

   config :friends, Friends.Repo,
     database: "friends",
     username: "alex",
     password: "AbC123dEf",
     hostname: "ep-cool-darkness-123456.us-west-2.aws.neon.tech",
     ssl: [cacerts: :public_key.cacerts_get()]

   The :ssl option is required to connect to Neon. Postgrex, since v0.18, verifies the server SSL certificate and you need to select CA trust store using :cacerts or :cacertfile options. You can use the OS-provided CA store by setting cacerts: :public_key.cacerts_get(). While not recommended, you can disable certificate verification by setting ssl: [verify: :verify_none].

2. The second part of the configuration generated by the mix ecto.gen.repo command is the Ecto.Repo module, found in lib/friends/repo.ex. You shouldn't have to make any changes here, but verify that the following configuration is present:

   defmodule Friends.Repo do
     use Ecto.Repo,
       otp_app: :friends,
       adapter: Ecto.Adapters.Postgres
   end

   Ecto uses the module definition to query the database. The otp_app setting tells Ecto where to find the database configuration. In this case, the :friends application is specified, so Ecto will use the configuration defined in the that application's config/config.exs file. The :adapter option defines the Postgres adapter.

3. Next, the Friends.Repo must be defined as a supervisor within the application's supervision tree. In lib/friends/application.ex, make sure Friends.Repo is specified in the start function, as shown:

   def start(_type, _args) do
     children = [
       Friends.Repo,
     ]

   This configuration starts the Ecto process, enabling it to receive and execute the application's queries.

4. The final part of the configuration is to add the following line under the configuration in the config/config.exs file that you updated in the first step:

   config :friends, ecto_repos: [Friends.Repo]

   This line tells the application about the new repo, allowing you to run commands such as mix ecto.migrate, which you will use in a later step to create a table in your database.

Create a migration and add a table

Your friends database is currently empty. It has no tables or data. In this step, you will add a table. To do so, you will create a "migration" by running the following command in your application directory:

mix ecto.gen.migration create_people

The command generates an empty migration file in priv/repo/migrations, which looks like this:

defmodule Friends.Repo.Migrations.CreatePeople do
  use Ecto.Migration

  def change do

  end
end

Add code to the migration file to create a table called people. For example:

defmodule Friends.Repo.Migrations.CreatePeople do
  use Ecto.Migration

  def change do
    create table(:people) do
      add :first_name, :string
      add :last_name, :string
      add :age, :integer
    end
  end
end

To run the migration and create the people table in your database, which also verifies your connection to Neon, run the following command from your application directory:

mix ecto.migrate

The output of this command should appear similar to the following:

14:30:04.924 [info]  == Running 20230524172817 Friends.Repo.Migrations.CreatePeople.change/0 forward
14:30:04.925 [info]  create table people
14:30:05.014 [info]  == Migrated 20230524172817 in 0.0s

You can use the Tables feature in the Neon Console to view the table that was created:

1. Navigate to the Neon Console.
2. Select a project.
3. Select Tables from the sidebar.
4. Select the Branch, Database (friends), and the schema (public). You should see the people table along with a schema_migration table that was created by the migration.

Application code

You can find the application code for the example above on GitHub.

• Neon Ecto Getting Started App

  Learn how to connect from Elixir with Ecto to Neon

Next steps

The Ecto Getting Started Guide provides additional steps that you can follow to create a schema, insert data, and run queries. See Creating the schema in the Ecto Getting Started Guide to pick up where the steps in this guide leave off.

Usage notes

• Suppose you have PGHOST environment variable on your system set to something other than your Neon hostname. In that case, this hostname will be used instead of the Neon hostname defined in your Ecto Repo configuration when running mix ecto commands. To avoid this issue, you can either set the PGHOST environment variable to your Neon hostname or specify PGHOST="" when running mix ecto commands; for example: PGHOST="" mix ecto.migrate.
• Neon's Scale to Zero feature scales computes to zero after 300 seconds (5 minutes) of inactivity, which can result in a connection not available error when running mix ecto commands. Typically, a Neon compute takes a few hundred milliseconds to transition from Idle to Active. Wait a second or two and try running the command again. Alternatively, consider the strategies outlined in Connection latency and timeouts to manage connection issues resulting from compute suspension.