## Atlas: A modern tool for managing database schemas

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Atlas is a language-agnostic tool for managing and migrating database schemas using modern DevOps principles.
It offers two workflows:

- **Declarative**: Similar to Terraform, Atlas compares the current state of the database to the desired state, as
defined in an [HCL], [SQL], or [ORM] schema. Based on this comparison, it generates and executes a migration plan to 
transition the database to its desired state.

- **Versioned**: Unlike other tools, Atlas automatically plans schema migrations for you. Users can describe their desired
database schema in [HCL], [SQL], or their chosen [ORM], and by utilizing Atlas, they can plan, lint, and apply the
necessary migrations to the database.

## Quick installation

**macOS + Linux:**

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

**Homebrew:**

```bash
brew install ariga/tap/atlas
```

**Docker:**

```bash
docker pull arigaio/atlas
```

**NPM:**

```bash
npx @ariga/atlas
```

Click [here](https://atlasgo.io/getting-started#installation) to read instructions for other platforms.

## Getting started
Get started with Atlas by following the [Getting Started](https://atlasgo.io/getting-started/) docs.
This tutorial teaches you how to inspect a database, generate a migration plan and apply the migration to your database.

## Key features:

- **Schema management**: The `atlas schema` command offers various options for inspecting, diffing, comparing, and modifying
  database schemas.
- **Versioned migration**: The `atlas migrate` command provides a state-of-the-art experience for planning, linting, and
  applying migrations.
- **Terraform support**: Managing database changes as part of a Terraform deployment workflow.
- **[SQL], [HCL] and [ORM] support**: Atlas enables users to define their desired database schema using [HCL], [SQL], or their chosen [ORM].
- **Multi-tenancy**: Atlas includes built-in support for multi-tenant database schemas.
- **Cloud integration**: Atlas integrates with standard cloud services and provides an easy way to read secrets from cloud
  providers such as AWS Secrets Manager and GCP Secret Manager.

## `schema inspect`
_**Easily inspect your database schema by providing a database URL and convert it to HCL, JSON or SQL.**_

Inspect a specific MySQL schema and get its representation in Atlas DDL syntax:
```shell
atlas schema inspect -u "mysql://root:pass@localhost:3306/example" > schema.hcl
```

<details><summary>Result</summary>

```hcl
table "users" {
  schema = schema.example
  column "id" {
    null = false
    type = int
  }
  ...
}
```
</details>

Inspect the entire MySQL database and get its JSON representation:
```shell
atlas schema inspect \
  --url "mysql://root:pass@localhost:3306/" \
  --format '{{ json . }}' | jq
```

<details><summary>Result</summary>

```json
{
  "schemas": [
    {
      "name": "example",
      "tables": [
        {
          "name": "users",
          "columns": [
            ...
          ]
        }
      ]
    }
  ]
}
```
</details>

Inspect a specific PostgreSQL schema and get its representation in SQL DDL syntax:
```shell
atlas schema inspect \
  --url "postgres://root:pass@:5432/test?search_path=public&sslmode=disable" \
  --format '{{ sql . }}'
```

<details><summary>Result</summary>

```sql
-- create "users" table
CREATE TABLE "users" ("id" integer NULL, ...);
-- create "posts" table
CREATE TABLE "posts" ("id" integer NULL, ...);
```
</details>

## `schema diff`
_**Compare two schema states and get a migration plan to transform one into the other. A state can be specified using a
database URL, HCL or SQL schema, or a migration directory.**_

Compare two MySQL schemas:
```shell
atlas schema diff \
  --from mysql://root:pass@:3306/db1 \
  --to mysql://root:pass@:3306/db2
```

<details><summary>Result</summary>

```sql
-- Drop "users" table
DROP TABLE `users`;
```
</details>

Compare a MySQL schema with a migration directory:
```shell
atlas schema diff \
  --from mysql://root:pass@:3306/db1 \
  --to file://migrations \
  --dev-url docker://mysql/8/db1
````

Compare a PostgreSQL schema with an Atlas schema in HCL format:
```shell
atlas schema diff \
  --from "postgres://postgres:pass@:5432/test?search_path=public&sslmode=disable" \
  --to file://schema.hcl \
  --dev-url "docker://postgres/15/test"
````

Compare an HCL schema with an SQL schema:
```shell
atlas schema diff \
  --from file://schema.sql \
  --to file://schema.hcl \ 
  --dev-url docker://postgres/15/test  
````

## `schema apply`
_**Generate a migration plan and apply it to the database to bring it to the desired state. The desired state can be
specified using a database URL, HCL or SQL schema, or a migration directory.**_

Update the database to the state defined in the HCL schema:
```shell
atlas schema apply \
  --url mysql://root:pass@:3306/db1 \
  --to file://schema.hcl \
  --dev-url docker://mysql/8/db1
```

<details><summary>Result</summary>

```shell
-- Planned Changes:
-- Modify "users" table
ALTER TABLE `db1`.`users` DROP COLUMN `d`, ADD COLUMN `c` int NOT NULL;
Use the arrow keys to navigate: ↓ ↑ → ← 
? Are you sure?: 
  ▸ Apply
    Abort
```
</details>

Update the database to the state defined in a specific version of the migration directory:
```shell
atlas schema apply \
  --url mysql://root:pass@:3306/db1 \
  --to "file://migrations?version=20221118091226" \
  --dev-url docker://mysql/8/db1
```

### Additional `schema` commands
Atlas offers additional commands to assist users managing their database schemas. These include `schema clean` and
`schema fmt`. For more information, see the versioned migration documentation at https://atlasgo.io/declarative/inspect.

## `migrate diff`
_**Write a new migration file to the migration directory that bring it to the desired state. The desired state can be
specified using a database URL, HCL or SQL schema, or a migration directory.**_

Create a migration file named `add_blog_posts` in the migration directory to bring the database to the state defined
in an HCL schema:
```shell
atlas migrate diff add_blog_posts \           
  --dir file://migrations \
  --to file://schema.hcl \
  --dev-url docker://mysql/8/test
```

Create a migration file named `add_blog_posts` in the migration directory to bring the database to the state defined
in an SQL schema:
```shell
atlas migrate diff add_blog_posts \           
  --dir file://migrations \
  --to file://schema.sql \
  --dev-url docker://mysql/8/test
```

Create a migration file named `add_blog_posts` in the migration directory to bring the database to the state defined
by another database:
```shell
atlas migrate diff add_blog_posts \           
  --dir file://migrations \
  --to mysql://root:pass@host:3306/db \
  --dev-url docker://mysql/8/test
```

## `migrate apply`
_**Apply all or part of pending migration files in the migration directory on the database.**_

Apply all pending migration files in the migration directory on a MySQL database:
```shell
atlas migrate apply \
  --url mysql://root:pass@:3306/db1 \
  --dir file://migrations
```

Apply in **dry run** mode the first the pending migration file in the migration directory on a PostgreSQL schema:
```shell
atlas migrate apply \
  --url "postgres://root:pass@:5432/test?search_path=public&sslmode=disable" \
  --dir file://migrations \
  --dry-run
```

### Additional `migrate` commands
Atlas offers additional commands to assist users managing their database migrations. These include `migrate lint`,
`migrate status`, and more. For more information, see the versioned migration documentation at https://atlasgo.io/versioned/diff.

### Supported databases
MySQL, MariaDB, PostgresSQL, SQLite, TiDB, CockroachDB, SQL Server.

[HCL]: https://atlasgo.io/atlas-schema/hcl
[SQL]: https://atlasgo.io/atlas-schema/sql
[ORM]: https://atlasgo.io/atlas-schema/external
