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バージョン管理型マイグレーション

Quick Guide​

Here are a few quick steps that explain how to auto-generate and execute migration files against a database. For a more in-depth explanation, continue reading the next section.

Generating migrations​

To install the latest release of Atlas, simply run one of the following commands in your terminal, or check out the Atlas website:

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

Then, run the following command to automatically generate migration files for your Ent schema:

atlas migrate diff migration_name \
  --dir "file://ent/migrate/migrations" \
  --to "ent://ent/schema" \
  --dev-url "docker://mysql/8/ent"
The role of the dev database Atlas loads the current state by executing the SQL files stored in the migration directory onto the provided dev database. It then compares this state against the desired state defined by the ent/schema package and writes a migration plan for moving from the current state to the desired state. :::

Applying migrations​

To apply the pending migration files onto the database, run the following command:

atlas migrate apply \
  --dir "file://ent/migrate/migrations" \
  --url "mysql://root:pass@localhost:3306/example"

For more information head over to the Atlas documentation.

Migration status​

Use the following command to get detailed information about the migration status of the connected database:

atlas migrate status \
  --dir "file://ent/migrate/migrations" \
  --url "mysql://root:pass@localhost:3306/example"

In Depth Guide​

Atlas マイグレーションエンジンを使用している場合、バージョン管理型マイグレーションを使用できます。 変更を直接データベースに適用するのではなく、Atlasはマイグレーションに必要な SQL 文を含むマイグレーションファイル群を生成します。 これらのファイルは、必要に応じて編集し、golang-migrate, Flyway, Liquibase などの既存のマイグレーションツールで適用できます

バージョン管理型マイグレーションファイルの生成​

マイグレーションファイルは、2つの状態の差分を計算することで生成されます。 Ent スキーマに反映されている状態を 望ましい 状態であり、現在 の状態は、直前の変更によるスキーマの最後の状態です。 Ent が現在の状態を判断する方法は 2 つあります。

  1. 既存のマイグレーションディレクトリを再実行し、スキーマを検査する (デフォルト)
  2. 既存のデータベースに接続し、スキーマを検査する

差分を作成するために本番データベースに接続する必要がないという利点があるため、最初のオプションを使用することを推奨します。 この方法は、異なるマイグレーション状態の複数のデプロイメントがある場合にも有効です。

atlas-versioned-migration-process

In order to automatically generate migration files, you can use one of the two approaches:

  1. Use Atlas migrate diff command against your ent/schema package.
  2. Enable the sql/versioned-migration feature flag and write a small migration generation script that uses Atlas as a package to generate the migration files.

Option 1: Use the atlas migrate diff command​

atlas migrate diff migration_name \
  --dir "file://ent/migrate/migrations" \
  --to "ent://ent/schema" \
  --dev-url "docker://mysql/8/ent"

上記のコマンドが正常に実行された後、ls ent/migrate/migrations を実行すると、Atlas が2つのファイルを作成していることが分かります。

-- create "users" table
CREATE TABLE `users` (`id` bigint NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`)) CHARSET utf8mb4 COLLATE utf8mb4_bin;

Head over to the Applying Migration Files section to learn how to execute the generated migration files onto the database.

Option 2: Create a migration generation script​

最初のステップは、機能フラグsql/versioned-migration を渡すことで、バージョン管理型マイグレーション機能を有効にすることです。 Ent コード生成ツールの実行方法によって、2 つの選択肢のうち どちらかを使用します。

デフォルトのgo generateの設定を使用している場合は、--feature sql/versioned-migration を ent/generate.go ファイルに追加するだけです。

package ent

//go:generate go run -mod=mod entgo.io/ent/cmd/ent generate --feature sql/versioned-migration ./schema

go generate を使ってコード生成を実行した後、マイグレーションファイルを作成するための新しいメソッドが、ent/migrate パッケージに追加されました。 次のステップは以下の通りです:

1. マイグレーションディレクトリを再実行し、現在の状態を計算するために、Atlas 開発用データベース へURLを提供します。 docker を使用して、ローカルにデータベースコンテナを立ち上げましょう

docker run --name migration --rm -p 3306:3306 -e MYSQL_ROOT_PASSWORD=pass -e MYSQL_DATABASE=test -d mysql

2. Create a file named main.go and a directory named migrations under the ent/migrate package and customize the migration generation for your project.

ent/migrate/main.go
//go:build ignore

package main

import (
    "context"
    "log"
    "os"

    "<project>/ent/migrate"

    atlas "ariga.io/atlas/sql/migrate"
    "entgo.io/ent/dialect"
    "entgo.io/ent/dialect/sql/schema"
    _ "github.com/go-sql-driver/mysql"
)

func main() {
    ctx := context.Background()
    // Create a local migration directory able to understand Atlas migration file format for replay.
    dir, err := atlas.NewLocalDir("ent/migrate/migrations")
    if err != nil {
        log.Fatalf("failed creating atlas migration directory: %v", err)
    }
    // Migrate diff options.
    opts := []schema.MigrateOption{
        schema.WithDir(dir),                         // provide migration directory
        schema.WithMigrationMode(schema.ModeReplay), // provide migration mode
        schema.WithDialect(dialect.MySQL),           // Ent dialect to use
        schema.WithFormatter(atlas.DefaultFormatter),
    }
    if len(os.Args) != 2 {
        log.Fatalln("migration name is required. Use: 'go run -mod=mod ent/migrate/main.go <name>'")
    }
    // Generate migrations using Atlas support for MySQL (note the Ent dialect option passed above).
    err = migrate.NamedDiff(ctx, "mysql://root:pass@localhost:3306/test", os.Args[1], opts...)
    if err != nil {
        log.Fatalf("failed generating migration file: %v", err)
    }
}

3. プロジェクトのルートから go run -mod=mod ent/migrate/main.go <name> を実行して、マイグレーション生成をトリガーする。 以下のように行います。

go run -mod=mod ent/migrate/main.go create_users

Run ls ent/migrate/migrations after the command above was passed successfully, and you will notice Atlas created 2 files:

-- create "users" table
CREATE TABLE `users` (`id` bigint NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`)) CHARSET utf8mb4 COLLATE utf8mb4_bin;

完全な例は GitHub repositoryにあります

マイグレーションの検証とリント​

Atlasでマイグレーションファイルを生成した後、atlas migrate lint コマンドを実行すると、マイグレーションディレクトリの中身を検証・分析し、 選択した変更に関するインサイトと診断結果が生成されます。

  1. マイグレーションを履歴の任意のタイミングから再実行できます
  2. 複数のチームメンバーが同時にマイグレーションをマイグレーションディレクトリに書き込む際に、期待しない履歴の変更から保護します。 一貫性チェックについての詳細は 以下のセクションを確認してください。
  3. 破壊的または不可逆的な変更が行われたか、またはテーブルの内容に依存し、マイグレーションに失敗する可能性があるかどうかを検出します。

atlas migrate lintに必要なパラメータを指定して、マイグレーション・リンティングを実行してみましょう。

  • --dev-url 変更を再現するために使用されるDev データベースのURL
  • --dir マイグレーションディレクトリのURL、デフォルトはfile://migrations
  • --dir-format ディレクトリフォーマット、デフォルトはatlas
  • (オプション) --log Goテンプレートを使用したカスタムロギング
  • (オプション) --latest 最新のN個のマイグレーションファイルに対して分析を実行
  • (オプション) --git-base ベースGitブランチに対して分析を実行

Install Atlas:​

To install the latest release of Atlas, simply run one of the following commands in your terminal, or check out the Atlas website:

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

Run the atlas migrate lint command:​

atlas migrate lint \
  --dev-url="docker://mysql/8/test" \
  --dir="file://ent/migrate/migrations" \
  --latest=1

このような実行の出力は、次のようになります:

20221114090322_add_age.sql: data dependent changes detected:

    L2: Adding a non-nullable "double" column "age" on table "users" without a default value implicitly sets existing rows with 0

20221114101516_add_name.sql: data dependent changes detected:

    L2: Adding a non-nullable "varchar" column "name" on table "users" without a default value implicitly sets existing rows with ""

A Word on Global Unique IDs​

This section only applies to MySQL users using the global unique id feature.

When using the global unique ids, Ent allocates a range of 1<<32 integer values for each table. This is done by giving the first table an autoincrement starting value of 1, the second one the starting value 4294967296, the third one 8589934592, and so on. The order in which the tables receive the starting value is saved in an extra table called ent_types. With MySQL 5.6 and 5.7, the autoincrement starting value is only saved in memory (docs, InnoDB AUTO_INCREMENT Counter Initialization header) and re-calculated on startup by looking at the last inserted id for any table. Now, if you happen to have a table with no rows yet, the autoincrement starting value is set to 0 for every table without any entries. With the online migration feature this wasn't an issue, because the migration engine looked at the ent_types tables and made sure to update the counter, if it wasn't set correctly. However, with versioned migration, this is no longer the case. In order to ensure, that everything is set up correctly after a server restart, make sure to call the VerifyTableRange method on the Atlas struct:

package main

import (
    "context"
    "log"

    "<project>/ent"
    "<project>/ent/migrate"
    "entgo.io/ent/dialect/sql"
    "entgo.io/ent/dialect/sql/schema"

    _ "github.com/go-sql-driver/mysql"
)

func main() {
    drv, err := sql.Open("mysql", "user:pass@tcp(localhost:3306)/ent")
    if err != nil {
        log.Fatalf("failed opening connection to mysql: %v", err)
    }
    defer drv.Close()
    // Verify the type allocation range.
    m, err := schema.NewMigrate(drv, nil)
    if err != nil {
        log.Fatalf("failed creating migrate: %v", err)
    }
    if err := m.VerifyTableRange(context.Background(), migrate.Tables); err != nil {
        log.Fatalf("failed verifyint range allocations: %v", err)
    }
    client := ent.NewClient(ent.Driver(drv))
    // ... do stuff with the client
}
Important

After an upgrade to MySQL 8 from a previous version, you still have to run the method once to update the starting values. Since MySQL 8 the counter is no longer only stored in memory, meaning subsequent calls to the method are no longer needed after the first one.

Apply Migration Files​

生成されたマイグレーションファイルをデータベースに適用するために、Atlas CLI の使用をお勧めします。 その他のマイグレーション管理ツールを使用したい場合、Ent にはいくつかのツールに適したマイグレーションを生成するためのサポートもあります。

atlas migrate apply \
  --dir "file://ent/migrate/migrations" \
  --url "mysql://root:pass@localhost:3306/example"

For more information head over to the Atlas documentation.

info

Ent の以前のバージョンでは、golang-migrate/migrateがデフォルトのマイグレーション実行エンジンでした。 簡単に移行できるように、Atlasは golang-migrate のマイグレーションフォーマットをインポートすることができます。 詳しくは、Atlasのドキュメントを参照してください。

Moving from Auto-Migration to Versioned Migrations​

In case you already have an Ent application in production and want to switch over from auto migration to the new versioned migration, you need to take some extra steps.

Create an initial migration file reflecting the currently deployed state​

To do this make sure your schema definition is in sync with your deployed version(s). Then spin up an empty database and run the diff command once as described above. This will create the statements needed to create the current state of your schema graph. If you happened to have universal IDs enabled before, any deployment will have a special database table named ent_types. The above command will create the necessary SQL statements to create that table as well as its contents (similar to the following):

CREATE TABLE `users` (`id` integer NOT NULL PRIMARY KEY AUTOINCREMENT);
CREATE TABLE `groups` (`id` integer NOT NULL PRIMARY KEY AUTOINCREMENT);
INSERT INTO sqlite_sequence (name, seq) VALUES ("groups", 4294967296);
CREATE TABLE `ent_types` (`id` integer NOT NULL PRIMARY KEY AUTOINCREMENT, `type` text NOT NULL);
CREATE UNIQUE INDEX `ent_types_type_key` ON `ent_types` (`type`);
INSERT INTO `ent_types` (`type`) VALUES ('users'), ('groups');

In order to ensure to not break existing code, make sure the contents of that file are equal to the contents in the table present in the database you created the diff from. For example, if you consider the migration file from above (users,groups) but your deployed table looks like the one below (groups,users):

idtype
1groups
2users

You can see, that the order differs. In that case, you have to manually change both the entries in the generated migration file.

Use an Atlas Baseline Migration​

If you are using Atlas as migration execution engine, you can then simply use the --baseline flag. For other tools, please take a look at their respective documentation.

atlas migrate apply \
  --dir "file://migrations"
  --url mysql://root:pass@localhost:3306/ent
  --baseline "<version>"

Atlas migration directory integrity file​

The Problem​

Suppose you have multiple teams develop a feature in parallel and both of them need a migration. If Team A and Team B do not check in with each other, they might end up with a broken set of migration files (like adding the same table or column twice) since new files do not raise a merge conflict in a version control system like git. The following example demonstrates such behavior:

atlas-versioned-migrations-no-conflict

Assume both Team A and Team B add a new schema called User and generate a versioned migration file on their respective branch.

20220318104614_team_A.sql
-- create "users" table
CREATE TABLE `users` (
    `id` bigint NOT NULL AUTO_INCREMENT,
    `team_a_col` INTEGER NOT NULL,
    PRIMARY KEY (`id`)
) CHARSET utf8mb4 COLLATE utf8mb4_bin;
20220318104615_team_B.sql
-- create "users" table
CREATE TABLE `users` (
    `id` bigint NOT NULL AUTO_INCREMENT,
     `team_b_col` INTEGER NOT NULL,
     PRIMARY KEY (`id`)
) CHARSET utf8mb4 COLLATE utf8mb4_bin;

If they both merge their branch into master, git will not raise a conflict and everything seems fine. But attempting to apply the pending migrations will result in migration failure:

mysql> CREATE TABLE `users` (`id` bigint NOT NULL AUTO_INCREMENT, `team_a_col` INTEGER NOT NULL, PRIMARY KEY (`id`)) CHARSET utf8mb4 COLLATE utf8mb4_bin;
[2022-04-14 10:00:38] completed in 31 ms

mysql> CREATE TABLE `users` (`id` bigint NOT NULL AUTO_INCREMENT, `team_b_col` INTEGER NOT NULL, PRIMARY KEY (`id`)) CHARSET utf8mb4 COLLATE utf8mb4_bin;
[2022-04-14 10:00:48] [42S01][1050] Table 'users' already exists

Depending on the SQL this can potentially leave your database in a crippled state.

The Solution​

Luckily, the Atlas migration engine offers a way to prevent concurrent creation of new migration files and guard against accidental changes in the migration history we call Migration Directory Integrity File, which simply is another file in your migration directory called atlas.sum. For the migration directory of team A it would look similar to this:

h1:KRFsSi68ZOarsQAJZ1mfSiMSkIOZlMq4RzyF//Pwf8A=
20220318104614_team_A.sql h1:EGknG5Y6GQYrc4W8e/r3S61Aqx2p+NmQyVz/2m8ZNwA=

The atlas.sum file contains the checksum of each migration file (implemented by a reverse, one branch merkle hash tree), and a sum of all files. Adding new files results in a change to the sum file, which will raise merge conflicts in most version controls systems. Let's see how we can use the Migration Directory Integrity File to detect the case from above automatically.

Please note, that you need to have the Atlas CLI installed in your system for this to work, so make sure to follow the installation instructions before proceeding. :::

In previous versions of Ent, the integrity file was opt-in. But we think this is a very important feature that provides great value and safety to migrations. Therefore, generation of the sum file is now the default behavior and in the future we might even remove the option to disable this feature. For now, if you really want to remove integrity file generation, use the schema.DisableChecksum() option.

In addition to the usual .sql migration files the migration directory will contain the atlas.sum file. Every time you let Ent generate a new migration file, this file is updated for you. However, every manual change made to the migration directory will render the migration directory and the atlas.sum file out-of-sync. With the Atlas CLI you can both check if the file and migration directory are in-sync, and fix it if not:

# If there is no output, the migration directory is in-sync.
atlas migrate validate --dir file://<path-to-your-migration-directory>
# If the migration directory and sum file are out-of-sync the Atlas CLI will tell you.
atlas migrate validate --dir file://<path-to-your-migration-directory>
Error: checksum mismatch

You have a checksum error in your migration directory.
This happens if you manually create or edit a migration file.
Please check your migration files and run

'atlas migrate hash'

to re-hash the contents and resolve the error.

exit status 1

If you are sure, that the contents in your migration files are correct, you can re-compute the hashes in the atlas.sum file:

# Recompute the sum file.
atlas migrate hash --dir file://<path-to-your-migration-directory>

Back to the problem above, if team A would land their changes on master first and team B would now attempt to land theirs, they'd get a merge conflict, as you can see in the example below:

atlas-versioned-migrations-no-conflict

You can add the atlas migrate validate call to your CI to have the migration directory checked continuously. Even if any team member would now forget to update the atlas.sum file after a manual edit, the CI would not go green, indicating a problem.