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Declarative Schema Migrations

With Atlas's declarative schema migrations (sometimes called state-based migrations), users don't need to manually craft SQL migration scripts. Instead, Atlas automatically plans and applies schema changes, safely transitioning the database from its current state to the desired state.

The desired schema state can be defined using an HCL or SQL schema definition, a database URL, external schemas like ORM, or a combination of these.

Declarative vs. Versioned Workflows

Read more about declarative workflows

Log in to Atlas

By default, the atlas schema apply command manages only schemas, tables, and their associated indexes and constraints such as foreign keys and checks.

Views, materialized views, functions, procedures, triggers, sequences, domains, extensions, and additional database features are available to Atlas Pro users. To include these resources in schema migrations, use the following command:

atlas login

Overview​

  1. Atlas loads the desired state into the provided dev database (--dev-url)
  2. Atlas compares this against the target database's current state by inspecting its schema
  3. Atlas plans a migration to get from the current state to the desired state
  4. Atlas prompts the user to approve and apply the migration plan to the target database

Flags​

When running schema apply, users may supply multiple parameters:

  • --url or -u (required) - URL of the database to be inspected.
  • --to (required) - URL(s) of the desired state. Can be defined using an HCL or SQL schema, a database URL, or external ORM.
  • --dev-url (required) - URL to the dev database.
  • --schema (may be supplied multiple times) - Specify which schema to inspect within the target database.
  • --exclude (may be supplied multiple times) - Filter out resources matching the given glob pattern.
  • --format - Go template to use to format the output.
  • --edit - Open the planned migration in the default editor, allowing the user to modify it.
  • --config - Path to the Atlas configuration file. Defaults to atlas.hcl in the current directory, if the --env flag is set.
  • --env - Environment to use from the Atlas configuration file.
  • --dry-run - Write and print the SQL statements of the migration plan without executing them on the target database.
  • --auto-approve - Apply the migration plan to the target database without first prompting the user for approval.

See detailed usage examples in the Examples section.

Approval Policy​

The schema apply command requires user review and approval before executing the migration against the target database.

Approving the migration can occur manually either locally or in CI, or automatically with the linting review policy. It can also be completely skipped, which is not recommended in production environments.

Let's cover all the options:

  1. Manual Review (default): The atlas schema apply command will print the SQL statements it is going to run and prompt the user for approval. Users can review the migration plan and either approve or reject it.

    Atlas Pro users can set the --dev-url flag to run an analysis and simulation of the proposed changes on the dev database and get a detailed linting report when reviewing the migration.

  2. Using Review Policy: Atlas ships with an analysis engine that can detect the impact of proposed changes to the target database. For example, Atlas can detect irreversible destructive changes that can result in data loss or data-dependent changes that may fail due to data integrity constraints.

    Users can configure Atlas to automatically approve migrations that pass the analysis engine checks (for example, no destructive changes were detected) and require manual review for migrations that fail the checks. Read more on how to configure the Review Policy for your project below.

  3. Skip Review: The --auto-approve flag can be used to skip the review process and automatically apply the migration to the target database. Although this option is convenient for experimentation and development, it is not recommended for production environments, as it may lead to unexpected changes.

Review Policy​

Atlas Pro users can define the cases in which their schema changes require manual review and approval. How does this work?

  1. During atlas schema apply, Atlas checks if there is an approved pre-planned migration for the given schema transition (State1 -> State2). If one exists, then Atlas will apply it without requiring manual review.
  2. If no migration has been pre-planned, Atlas will lint the schema changes by running an analysis and simulation on the dev database to review their potential impact on the target database.
  3. Atlas then prints the linting report and, based on the review policy defined in the atlas.hcl file, decides whether to auto-approve the migration or require manual review.

The review policy can be set to one of the following values:

  • ERROR - Atlas will require manual review and approval only if the linting report contains errors. See the Destructive Changes analyzer as an example.
  • WARNING - Atlas will require manual review and approval if the linting report contains warnings (diagnostics) or errors. See the list of checks that can result in warnings.
  • ALWAYS (default) - Atlas will always require manual review and approval, regardless of the linting report.
atlas.hcl
lint {
  review = ERROR // ERROR | WARNING | ALWAYS
  destructive {
    error = false
  }
}

The typical workflow for applying schema changes without manual review is to run atlas schema plan to pre-plan the migration and use the review policy as a fall-back for schema transitions that were not pre-planned but are still safe to apply.

The atlas schema plan command can be integrated into the CI/CD pipeline to ensure that all schema changes are reviewed and approved before being applied to the database.

Diff Policy​

Atlas allows configuring the schema diffing policy in project configuration to fine-tune or modify suggested changes before applying them to the database:

To instruct Atlas to skip destructive statements, specifically DROP SCHEMA or DROP TABLE in this example, via a CLI variable, define a variable in the project configuration and set its value dynamically when running the migrate diff command:

atlas.hcl
variable "destructive" {
  type    = bool
  default = false
}

env "local" {
  diff {
    skip {
      drop_schema = !var.destructive
      drop_table  = !var.destructive
    }
  }
}

The usage is as follows:

atlas schema apply --env "local" --var "destructive=true"

Transaction Configuration​

Similar to the migrate apply command, the schema apply command allows configuring the transaction mode for declarative migrations using the --tx-mode flag. The following options are available:

  • --tx-mode file (default) wraps the planned migration in its own transaction. If a statement fails, the transaction is rolled back, and Atlas stops execution.
  • --tx-mode none will not create any transaction.

Examples​

HCL Schema as Desired State​

The following example demonstrates how to use Atlas DDL (HCL) as the desired state:

atlas schema apply \
  --url "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable" \
  --to "file://schema.hcl" \
  --dev-url "docker://postgres/15"

SQL Schema as Desired State​

The following example demonstrates how to use an SQL schema file as the desired state:

atlas schema apply \
  --url "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable" \
  --to "file://schema.sql" \
  --dev-url "docker://postgres/15"

ORM Schema as Desired State​

The following example demonstrates how to use Sequelize models as the desired state:

atlas.hcl
data "external_schema" "sequelize" {
  program = [
    "npx",
    "@ariga/atlas-provider-sequelize",
    "load",
    "--path", "./path/to/models",
    "--dialect", "postgres", // mariadb | mysql | sqlite | mssql
  ]
}

env "sequelize" {
  src = data.external_schema.sequelize.url
  dev = "docker://postgres/15"
  migration {
    dir = "file://migrations"
  }
  format {
    migrate {
      diff = "{{ sql . \"  \" }}"
    }
  }
}
atlas schema apply \
  --env sequelize \
  --url "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable"

To see this in action, check out our Declarative Migrations for Sequelize.js video.

For more ORM examples, go to our ORM guides.

Migration Directory as Desired State​

The following example demonstrates how to use the migration directory as the desired state.

atlas schema apply \
  --url "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable" \
  --to "file://migrations" \
  --dev-url "docker://postgres/15"

The URL for the migration directory can also contain two optional query parameters:

  • format - Migration directory format: atlas (default), golang-migrate, goose, dbmate, flyway, or liquibase.
  • version - Version number of the last migration file to read. By default, all migrations are read.

For example, "file://migrations?format=golang-migrate&version=20250909104354“

Multi-Tenant Environments​

The Atlas configuration language provides built-in support for executing declarative workflows in multi-tenant environments. Using the for_each meta-argument, users can define a single env block that is expanded to N instances – one for each tenant:

env "prod" {
  for_each = toset(var.tenants)
  url      = urlsetpath(var.url, each.value)
  src      = "schema.hcl"
  format {
    schema {
      apply = format(
        "{{ json . | json_merge %q }}",
        jsonencode({
          Tenant : each.value
        })
      )
    }
  }
  // Inject custom variables to the schema.hcl defined below.
  tenant = each.value
}

Read more about defining declarative workflows using project files in multi-tenant environments.

Reference​

CLI Command Reference