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

``sh
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:

`js
// 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:

`js
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.

`js
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.

$3

`js
const postgrator = new Postgrator(options);
`

| Option | Required | Description | default |
| ------------------ | -------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------- |
| migrationPattern | Required | Glob pattern to migration files. e.g. path.join(__dirname, '/migrations/*') | |
| driver | Required | Must be pg, mysql, mssql, or sqlite3 | |
| database | Required | Target database name. Optional for sqlite3. | |
| execQuery | Required | Function to execute SQL. MUST return a promise containing an object with a rows array of objects. For example { rows: [{ column_name: 'column_value' }] } | |
| execSqlScript | Optional | Function to execute db migration script consisting of multiple SQL statements. MUST return a void promise. If not supplied, execQuery will be used. | |
| schemaTable | Optional | Table created to track schema version. When using Postgres, you may specify schema as well, e.g. schema_name.table_name | schemaversion |
| validateChecksum | Optional | Validates checksum of existing SQL migration files already run prior to executing migrations. Set to false to disable. Unused for JS migrations. | true |
| newline | Optional | Force line ending on file when generating checksum. Value should be either CRLF (windows) or LF (unix/mac). | |
| currentSchema | Optional | For Postgres and MS SQL Server. Specifies schema to look to when validating schemaversion table columns. For Postgres, run's SET search_path = currentSchema prior to running queries against db |

$3

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.

$3

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

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

$3

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

`js
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));
`

$3

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).

$3

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.

$3

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

`js
// 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.

`sh


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