MyMigrator

MyMigrator is a simple database migration tool for managing MySQL database schema changes in Node.js projects using mysql2/promise. It helps to ensure that database migrations are applied in order and prevents accidental modifications to previously run migrations.

Installation

You can install the migration tool as an npm package:

npm install my-migrator

Usage

1. Import the DbMigration class

import { DbMigration } from "my-migrator";
import { createPool } from "mysql2/promise";

2. Create a connection pool to your MySQL database

const pool = createPool({
  host: "localhost",
  user: "root",
  password: "password",
  database: "your_database",
  // multipleStatements: true, // Allows executing multiple SQL statements in a single query
});

3. Initialize the migration instance

The DbMigration class requires two arguments:

• pool: The MySQL connection pool.
• dir: The directory where your migration files are stored.

const migrationDir = path.join(__dirname, "migrations");
const dbMigration = new DbMigration(pool, migrationDir);

4. Create your migration files

Migration files must follow a specific naming convention for the tool to recognize and process them. The correct naming format is:

V<number>__<description>.sql

For example:

V1__create_table_users.sql
V2__add_column_email_to_users.sql

Each migration file should contain valid SQL statements for the database changes you want to apply.

Here’s how you can update the section with a warning to ensure the user understands that the application should stop running if a migration fails:

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5. Run migrations

To apply the pending migrations, call the run() method of the DbMigration instance.

(async () => {
  try {
    await dbMigration.run();
  } catch (error) {
    console.error("Migration failed:", error);
  }
})();

Important: If an error occurs during the migration, do not edit or delete any existing migration files that have already been installed in the database. Instead, you should create a new migration file to fix the issue rather than modifying the one that caused the error. Editing an already-installed migration file will lead to the following error:

Error: Migrations have been edited after being installed in ⚠️ V3__create_post_table.sql⚠️
        🙏please revert the changes and try again

To resolve the error:

1. Leave the problematic migration file as is.
2. Create a new migration file that fixes the issue.
3. Re-run the migration process to apply the new changes.

This ensures that the migration history remains consistent, preventing further errors and maintaining the integrity of the database.

Migration Details

• Automatic Checksums: Each migration file's content is hashed using SHA256 and stored in the database to ensure no tampering occurs. If a previously installed migration file is edited or deleted, the tool will throw an error, preventing inconsistent migrations.
• Schema History Table: A schema_history table is automatically created in the database to track applied migrations, their versions, file names, and checksums. Below is an example of the schema_history table:

mysql> select * from schema_history;

version	file_name	check_sum	installed_by	installed_in	success
1	V1__create_test_table.sql	b4af9bdc0c7f329322cb1beb4413ba129acbc1fce4263828bf117dbd9ca218a6	admin	2024-09-08 16:19:34	1
2	V2__create_post_table.sql	be5f8428ee1311b9067b6176ae62794f3cdff552e846d8b906693b33c38ab428	admin	2024-09-08 16:19:34	0
3	V3__create_post_table.sql	63115d3fe315f39956249a792a183bb905cd5b66e82432087febea49b424cd5c	admin	2024-09-08 16:19:55	1

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• Columns Explained:
  • version: The version number of the migration.
  • file_name: The name of the migration file.
  • check_sum: The SHA256 hash of the migration file’s content to detect changes.
  • installed_by: The username that applied the migration (retrieved from environment variables or set as "unknown").
  • installed_in: The timestamp of when the migration was applied.
  • success: Whether the migration was applied successfully (1 for success, 0 for failure).

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This table helps track all applied migrations, ensuring the integrity of the database schema.

Error Handling

If any of the migrations fail, the tool will:

1. Print the error message to the console: The exact reason for the failure will be logged.
2. Terminate the database connection: The tool will stop further migration execution and close the database connection.
3. Require a new migration file: The failed migration will not be rolled back automatically. To fix the issue, you must create a new migration file rather than modifying or deleting the failed one.

Important: Once a migration fails:

• Do not edit the migration file that caused the error.
• Create a new migration file to resolve the issue.

Attempting to modify or delete the failed migration file will result in the following error when re-running the migration:

Error: Migrations have been edited after being installed in ⚠️ V2__create_post_table.sql⚠️
        🙏please revert the changes and try again

The migration process is designed this way to ensure the integrity of the database and maintain a clear history of changes.

Example of Running Migrations

Here's a full example of how to use the DbMigration tool:

import { DbMigration } from "my-migrator";
import { createPool } from "mysql2/promise";
import path from "path";

(async () => {
  const pool = createPool({
    host: "localhost",
    user: "root",
    password: "password",
    database: "my_database",
  });

  const migrationDir = path.join(__dirname, "migrations");

  const dbMigration = new DbMigration(pool, migrationDir);

  await dbMigration.run();
  await pool.end();
})();

Important Notes

• File Naming: Make sure the migration files follow the V<number>__<description>.sql pattern. Any file that doesn't match this pattern will cause an error.
• Checksum Integrity: Once a migration file is applied, do not modify its content. The tool compares checksums of installed migrations to detect any changes.
• Database Schema Table: Ensure the schema_history table is created in the correct database. The tool handles this automatically, but it’s crucial to use the same database in your connection pool.

License

This project is licensed under the MIT License.

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Contributing

Feel free to submit pull requests or open issues to improve this project.

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