Skip to main content

External Integrations

Atlas allows loading the desired state of the database schema from external programs or ORMs, regardless of the programing language they are written in. Once the schema is loaded, it can be used by the various Atlas commands such as atlas schema and atlas migrate.

Loading an External Schema

In order to load an external schema, you need first to create an atlas.hcl config file, if you don't already have one and declare a new data source of type external_schema that can be used later as the desired state. Let's explain this with an example.

Given the following atlas.hcl file:

data "external_schema" "orm" {
# The first argument is the command to run,
# and the rest are optional arguments.
program = [

env "orm" {
src = data.external_schema.orm.url
dev = "docker://mysql/8/dev"

Let's explain what is happening when running atlas with the --env orm command:

  1. The external_schema.orm data source is loaded, by running the command npm run generate-schema and capturing its output as the desired state of the schema.

  2. The program output should be defined as a list of SQL DDL statements separated by semicolon (;) or a custom delimiter. More info about the format can be found in the SQL schema page. For example:

    CREATE TABLE users (id int PRIMARY KEY, name text NOT NULL);

    CREATE TABLE posts (id int PRIMARY KEY, content text NOT NULL, author_id int NOT NULL REFERENCES users(id));
  3. After the schema is loaded, Atlas utilizes the dev-database to parse and validate the SQL definition and converts them into its internal graph representation.

  4. The loaded schema can be used by the various Atlas commands. For example:

    # Generating a new migration.
    atlas migrate diff --env orm
    # Applying the schema to the database.
    atlas schema apply --env orm

Write an external loader

Most ORMs offer a way to generate a series of DDL statements from model definitions. For example, Java Hibernate enables "schema exporting" using the hbm2ddl option, and Microsoft EF supplies a helper method called GenerateCreateScript that lets users craft a small script to produce DDLs from their EF models. In a similar way, TypeORM users can use the createSchemaBuilder().log() API, and so on.

A fully working implementation can be found in the atlas-provider-gorm repository, which is an external loader for the GORM ORM.