Using Postgres Extensions in Ent Schema

Using Postgres Extensions in Ent Schema

Postgres extensions are add-on modules that extend the functionality of the database by providing new data types, operators, functions, procedural languages, and more.

This guide explains how to define a schema field that uses a data type provided by the PostGIS extension, and configure the schema migration to manage both Postgres extension installations and the Ent schema as a single migration unit using Atlas.

Atlas Pro Feature

Atlas support for Extensions is available exclusively to Pro users. To use this feature, run:

atlas login

Install Atlas

To install the latest release of Atlas, simply run one of the following commands in your terminal, or check out the Atlas website:

macOS + Linux
Homebrew
Docker
Windows

curl -sSf https://atlasgo.sh | sh

brew install ariga/tap/atlas

docker pull arigaio/atlas
docker run --rm arigaio/atlas --help

If the container needs access to the host network or a local directory, use the --net=host flag and mount the desired directory:

docker run --rm --net=host \
  -v $(pwd)/migrations:/migrations \
  arigaio/atlas migrate apply
  --url "mysql://root:pass@:3306/test"

Download the latest release and move the atlas binary to a file location on your system PATH.

$ atlas login a8m
You are now connected to "a8m" on Atlas Cloud.

Composite Schema

An ent/schema package is mostly used for defining Ent types (objects), their fields, edges and logic. Extensions like postgis or hstore do not have representation in Ent schema. A Postgres extension can be installed once in your Postgres database, and may be used multiple times in different schemas.

In order to extend our PostgreSQL schema migration to include both extensions and our Ent types, we configure Atlas to read the state of the schema from a Composite Schema data source. Follow the steps below to configure this for your project:

Create a schema.sql that defines the necessary extensions used by your database. In the same way, you can define the extensions in Atlas Schema HCL language:

Using SQL
Using HCL

schema.sql

-- Install PostGIS extension.
CREATE EXTENSION postgis;

schema.hcl

schema "public" {}
extension "postgis" {
  schema  = schema.public
  version = "3.4.2"
  comment = "PostGIS geometry and geography spatial types and functions"
}

In your Ent schema, define a field that uses the data type provided by the extension. In this example, we use the GEOMETRY(Point, 4326) data type provided by the postgis extension:

ent/schema/user.go

// Fields of the User.
func (User) Fields() []ent.Field {
    return []ent.Field{
        field.Bytes("location").
            // Ideally, we would use a custom GoType
            // to represent the "geometry" type.
            SchemaType(map[string]string{
                dialect.Postgres: "GEOMETRY(Point, 4326)",
            }),
    }
}

Create a simple atlas.hcl config file with a composite_schema that includes both the extensions defined in schema.sql and your Ent schema:

atlas.hcl

data "composite_schema" "app" {
  # Install extensions first (PostGIS).
  schema "public" {
    url = "file://schema.sql"
  }
  # Then, load the Ent schema.
  schema "public" {
    url = "ent://ent/schema"
  }
}
env "local" {
  src = data.composite_schema.app.url
  dev = "docker://postgis/latest/dev"
  format {
    migrate {
      diff = "{{ sql . \"  \" }}"
    }
  }
}

Usage

After setting up our composite schema, we can get its representation using the atlas schema inspect command, generate schema migrations for it, apply them to a database, and more. Below are a few commands to get you started with Atlas:

Inspect the Schema

The atlas schema inspect command is commonly used to inspect databases. However, we can also use it to inspect our composite_schema and print the SQL representation of it:

atlas schema inspect \
  --env local \
  --url env://src \
  --format '{{ sql . }}'

The command above prints the following SQL.

-- Add new schema named "public"
CREATE SCHEMA IF NOT EXISTS "public";
-- Set comment to schema: "public"
COMMENT ON SCHEMA "public" IS 'standard public schema';
-- Create extension "postgis"
CREATE EXTENSION "postgis" WITH SCHEMA "public" VERSION "3.4.2";
-- Create "users" table
CREATE TABLE "public"."users" ("id" bigint NOT NULL GENERATED BY DEFAULT AS IDENTITY, "location" public.geometry(point,4326) NOT NULL, PRIMARY KEY ("id"));

Extensions Are Database-Level Objects

Although the SCHEMA argument is supported by the CREATE EXTENSION command, it only indicates where the extension’s objects will be installed. The extension itself is installed at the database level and cannot be loaded multiple times into different schemas.

Therefore, to avoid conflicts with other schemas, when working with extensions, the scope of the migration should be set to the database, where objects are qualified with the schema name. Hence, the search_path is dropped from the dev-database URL in the atlas.hcl file.

Generate Migrations For the Schema

To generate a migration for the schema, run the following command:

atlas migrate diff \
  --env local

Note that a new migration file is created with the following content:

migrations/20240712090543.sql

-- Create extension "postgis"
CREATE EXTENSION "postgis" WITH SCHEMA "public" VERSION "3.4.2";
-- Create "users" table
CREATE TABLE "public"."users" (
  "id" bigint NOT NULL GENERATED BY DEFAULT AS IDENTITY,
  "location" public.geometry(point,4326) NOT NULL,
  PRIMARY KEY ("id")
);

Apply the Migrations

To apply the migration generated above to a database, run the following command:

atlas migrate apply \
  --env local \
  --url "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable"

Apply the Schema Directly on the Database

Sometimes, there is a need to apply the schema directly to the database without generating a migration file. For example, when experimenting with schema changes, spinning up a database for testing, etc. In such cases, you can use the command below to apply the schema directly to the database:

atlas schema apply \
  --env local \
  --url "postgres://postgres:pass@localhost:5432/database?sslmode=disable"

Or, using the Atlas Go SDK:

ac, err := atlasexec.NewClient(".", "atlas")
if err != nil {
    log.Fatalf("failed to initialize client: %w", err)
}
// Automatically update the database with the desired schema.
// Another option, is to use 'migrate apply' or 'schema apply' manually.
if _, err := ac.SchemaApply(ctx, &atlasexec.SchemaApplyParams{
    Env: "local",
    URL: "postgres://postgres:pass@localhost:5432/database?sslmode=disable",
}); err != nil {
    log.Fatalf("failed to apply schema changes: %w", err)
}

The code for this guide can be found in GitHub.

Extensions