Atlas allows loading the desired state of the database schema from external programs or ORMs, regardless of theprograming language they are written in. Once the schema is loaded, it can be used by the various Atlas commandssuch asatlas schema andatlas migrate.

Loading an External Schema​

In order to load an external schema, you need first to create anatlas.hclconfig file, if you don'talready have one and declare a new data source of typeexternal_schema thatcan be used later as the desired state. Let's explain this with an example.

Given the followingatlas.hcl file:

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

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

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

env"orm"{
src= data.external_schema.orm.url
dev="docker:/maria/latest/dev"
}

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

env"orm"{
src= data.external_schema.orm.url
dev="docker://postgres/15/dev?search_path=public"
}

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

env"orm"{
src= data.external_schema.orm.url
dev="sqlite://dev?mode=memory"
}

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

1. Theexternal_schema.orm data source is loaded, by running the commandnpm run generate-schema andcapturing 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 acustom delimiter. More info about the format can be found intheSQL schema page. For example:

   CREATETABLE users(idintPRIMARYKEY, nametextNOTNULL);
   
   CREATETABLE posts(idintPRIMARYKEY, contenttextNOTNULL, author_idintNOTNULLREFERENCES users(id));
   
3. After the schema is loaded, Atlas utilizes thedev-database to parse and validate theSQL 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 migratediff--env orm
   # Applying the schema to the database.
   atlas schema apply--env orm
   

Supported ORMs​

Atlas supports loading the desired schema from popular ORMs in various languages. Developers who connect their ORM toAtlas can use it to automatically plan schema migrations based on the desired state defined in the ORM, rather thancrafting them by hand. The supported ORMs are:

Coming soon are Laravel and Drizzle. If you are using an ORM that is not listed here and would like to seeit supported,let us know!

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 thehbm2ddl option, and Microsoft EF supplies a helper method calledGenerateCreateScriptthat lets users craft a small script to produce DDLs from their EF models. In a similar way, TypeORM users can usethecreateSchemaBuilder().log() API, and so on.

A fully working implementation can be found in theatlas-provider-gormrepository, which is an external loader for theGORM ORM.