Postgrator

A Node.js SQL migration library using a directory of plain SQL scripts. Supports Postgres, MySQL, SQL Server, and SQLite.

Available as a CLI tool: https://www.npmjs.com/package/postgrator-cli.

Installation

npm install postgrator

Usage

Create a directory and stick some SQL scripts in there that change your database in some way. It might look like:

migrations/
  |- 001.do.sql
  |- 001.undo.sql
  |- 002.do.optional-description-of-script.sql
  |- 002.undo.optional-description-of-script.sql
  |- 003.do.sql
  |- 003.undo.sql
  |- 004.do.js
  |- 004.undo.js
  |- ... and so on

The files must follow the convention [version].[action].[optional-description].sql or [version].[action].[optional-description].js (or .mjs, .cjs)

Version must be a number, but you may start and increment the numbers in any way you'd like. If you choose to use a purely sequential numbering scheme instead of something based on a timestamp, you will find it helpful to start with 000s or some large number for file organization purposes.

Action must be either "do" or "undo". Do implements the version, and undo undoes it. In other migration tools, this might be "up" and "down". Writing undo scripts is optional if your dev/migration strategy does not require it.

Optional-description can be a label or tag to help keep track of what happens inside the script. Descriptions should not contain periods.

SQL or JS You have a choice of either using a plain SQL file or you can also generate your SQL via a javascript module. The javascript module should export a function called generateSql() that returns a string representing the SQL.

Note: As of version 6.0.0, postgrator is an ES module, and uses import() to load js migrations. .mjs and .cjs should be honored.

For example:

// Assuming commonJS module
module.exports.generateSql = function () {
  return (
    "CREATE USER transaction_user WITH PASSWORD '" +
    process.env.TRANSACTION_USER_PASSWORD +
    "'"
  );
};

You might want to choose the JS file approach, to make use of (secret) environment variables such as the above.

When using JS files, the file content nor the resulting script is checksum validated.

Support for asynchronous functions is provided, in the event you need to retrieve data from an external source, for example:

import axios from "axios";

module.exports.generateSql = async () => {
  const response = await axios({
    method: "get",
    url: "https://api.example.org/person/1",
  });
  return `INSERT INTO person (name, age) VALUES ('${response.data.name}', ${response.data.age});`;
};

To run your SQL migrations with Postgrator, write a Node.js script or integrate Postgrator with your application.

When first run against your database, Postgrator will create the table specified by config.schemaTable. Postgrator relies on this table to track what version the database is at.

Postgrator automatically determines whether it needs to go "up" or "down", and will update the schemaTable accordingly. If the database is already at the version specified to migrate to, Postgrator does nothing.

import Postgrator from "postgrator";
import pg from "pg";
import { dirname } from "path";
import { fileURLToPath } from "url";

const __dirname = dirname(fileURLToPath(import.meta.url));

async function main() {
  // Create a client of your choice
  const client = new pg.Client({
    host: "localhost",
    port: 5432,
    database: "postgrator",
    user: "postgrator",
    password: "postgrator",
  });

  try {
    // Establish a database connection
    await client.connect();

    // Create postgrator instance
    const postgrator = new Postgrator({
      migrationPattern: __dirname + "/some/pattern/*",
      driver: "pg",
      database: "databasename",
      schemaTable: "schemaversion",
      execQuery: (query) => client.query(query),
      execSqlScript: (sqlScript) => client.sqlScript(sqlScript),
    });

    // Migrate to specific version
    const appliedMigrations = await postgrator.migrate("002");
    console.log(appliedMigrations);

    // Or migrate to max version (optionally can provide 'max')
    await postgrator.migrate();
  } catch (error) {
    // If error happened partially through migrations,
    // error object is decorated with appliedMigrations
    console.error(error.appliedMigrations); // array of migration objects
  }

  // Once done migrating, close your connection.
  await client.end();
}
main();

Want more examples for MySQL and MS SQL Server? Check out the examples directory.

Options

const postgrator = new Postgrator(options);

Checksum validation

By default, Postgrator will generate an md5 checksum for each migration file and save the value to the schema table after a successful migration.

Before applying migrations to a database, Postgrator will validate the md5 checksum to ensure the scripts have not changed for any already run existing migrations in the migration directory. If a change is detected, migration will stop, reporting an error.

Because line endings may differ between environments/editors, an option is available to force a specific line ending prior to generating the checksum.

Migration object

Postgrator will often return a migration object or array of migrations. The format of a migration object is:

{
  version: versionNumber,
  action: 'do',
  name: 'first-table',
  filename: 'path/to/0001.up.first-table.sql',
  md5: 'checksumvalue',
  getSql: () => {} // function to get sql from file
}

Logging

Postgrator is an event emitter, allowing you to log however you want to log. There are no events for error or finish.

const postgrator = new Postgrator(options);
postgrator.on("validation-started", (migration) => console.log(migration));
postgrator.on("validation-finished", (migration) => console.log(migration));
postgrator.on("migration-started", (migration) => console.log(migration));
postgrator.on("migration-finished", (migration) => console.log(migration));

Migration errors

If postgrator.migrate() fails to run multiple migrations, Postgrator will stop running any further migrations. Migrations successfully run prior to the migration with the error will remain implemented.

If you need to migrate back to the version the database was at prior to running migrate(), that is up to you to implement. Instead of doing this consider writing your application in a way that is compatible with any version of a future release.

In the event of an error during migration, the error object will be decorated with an array of migrations that run successfully (error.appliedMigrations).

Keep in mind how you write your SQL - You may (or may not) want to write your SQL defensively (ie, check for pre-existing objects before you create new ones).

Preventing partial migrations

Depending on your database and database configuration, consider wrapping each migration in a transaction or BEGIN/END block. By default, Postgres and SQL Server consider multiple statements run in one execution part of one implicit transaction. MySQL however will implement up to the failure.

If using SQL Server, do not write a migration containing multiple statements using the GO keyword. Instead, break statements between the GO keyword into multiple migration files, ensuring that you do not end up with partial migrations implemented but no record of that happening.

Utility methods

Some of postgrator's methods may come in useful performing other migration tasks

// Get max version available from filesystem, as number, not string
const maxVersionAvailable = await postgrator.getMaxVersion();
console.log(maxVersionAvailable);

// "current" database schema version as number, not string
const version = await postgrator.getDatabaseVersion();
console.log(version);

// To get all migrations from directory and parse metadata
const migrations = await postgrator.getMigrations();
console.log(migrations);

Tests

A docker-compose file is provided with containers configured for tests.

To run Postgrator tests locally, you'll need Docker and Docker Compose installed.

# In one terminal window
docker-compose up
# In another terminal once databases are up
npm test
# After tests, in docker session
# control/command-c to quit docker-compose and remove containers
docker-compose rm --force

License

MIT