Using Postgres Extensions in GORM

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 GORM models 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

Getting started with Atlas and GORM

Before we continue to extensions, ensure you have installed the Atlas GORM Provider on your GORM project.

To set up, follow along the getting started guide for GORM and Atlas.

Composite Schema

The GORM package is mostly used for defining tables (our Go types) and interacting with the database. Extensions like postgis or hstore do not have representation in GORM. 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 GORM 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:

1. 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"
}

2. In your GORM model, define a field that uses the data type provided by the extension.

models.go
package models

import (
	"database/sql/driver"
	"fmt"
	"gorm.io/gorm"
)

// GeometryPoint is a custom GORM type for PostGIS point
type GeometryPoint struct {
	X float64 `json:"x"`
	Y float64 `json:"y"`
}

// Scan implements the Scanner interface for GeometryPoint
func (g *GeometryPoint) Scan(val interface{}) error {
	var point string
	switch v := val.(type) {
	case []byte:
		point = string(v)
	case string:
		point = v
	default:
		return fmt.Errorf("cannot convert %T to GeometryPoint", val)
	}

	_, err := fmt.Sscanf(point, "POINT(%f %f)", &g.X, &g.Y)
	return err
}

// Value implements the driver Valuer interface for GeometryPoint
func (g GeometryPoint) Value() (driver.Value, error) {
	return fmt.Sprintf("POINT(%f %f)", g.X, g.Y), nil
}

type User struct {
	gorm.Model
	Location GeometryPoint `gorm:"type:geometry(POINT, 4326)"` // Using PostGIS geometry type
}

3. In your atlas.hcl config file, add a composite_schema that includes both your extensions defined in schema.sql and your GORM model:

atlas.hcl
data "composite_schema" "app" {
  # Load first custom types first.
  schema "public" {
    url = "file://schema.sql"
  }
  schema "public" {
    url = data.external_schema.gorm.url
  }
}

env "local" {
  src = data.composite_schema.app.url
  dev = "docker://postgis/latest/dev"
}

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" bigserial NOT NULL, "created_at" timestamptz NULL, "updated_at" timestamptz NULL, "deleted_at" timestamptz NULL, "location" public.geometry(point,4326) NULL, PRIMARY KEY ("id"));
-- Create index "idx_users_deleted_at" to table: "users"
CREATE INDEX "idx_users_deleted_at" ON "public"."users" ("deleted_at");

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" bigserial NOT NULL, "created_at" timestamptz NULL, "updated_at" timestamptz NULL, "deleted_at" timestamptz NULL, "location" public.geometry(point,4326) NULL, PRIMARY KEY ("id"));
-- Create index "idx_users_deleted_at" to table: "users"
CREATE INDEX "idx_users_deleted_at" ON "public"."users" ("deleted_at");

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?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)
}

Getting started with Atlas and GORM​

Composite Schema​

Usage​

Inspect the Schema​

Generate Migrations For the Schema​

Apply the Migrations​