A minimalistic promise based database migration tool for rethinkdb
JavaScript Other
Latest commit 9177c80 Aug 7, 2016 @daerion 1.1.0

README.md

reconsider

js-standard-style

Reconsider is a minimalistic promise based database migration tool for rethinkdb that is meant to be called programmatically. Currently there is no CLI for it, though I am willing to add one if there is any sort of demand for it.

Reconsider is not currently compatible with the native rethinkdb driver but instead requires rethinkdbdash.

Installation

npm install --save reconsider

Usage

Defining Migrations

Each migration must be a module exporting an object with an up and a down function, residing in the configured migrations directory (migrations/ by default). Both methods will be passed the rethinkdb driver instance as their first parameter, and the logger instance as the second one. Since all the database operations performed in a migration are inherently async, both methods must return a Promise.

Sample Migration File

// File migrations/001-create-tables.js

'use strict'

const tableName = 'my_table'

module.exports = {
  up: function (r, logger) {
    logger.verbose(`Creating table ${tableName}.`)

    return r.tableCreate(tableName).run()
      .then(() => r.table(tableName).indexCreate('some_property').run())
  },

  down: function (r, logger) {
    logger.verbose(`Dropping table ${tableName}.`)

    return r.tableDrop(tableName).run()
  }
}

Running Migrations

When instantiating the Reconsider class, you must provide it with an already connected rethinkdbdash object and a database name. Reconsider will attempt to create both the database and it's own migrations table if either don't exist.

import rethinkdb from 'rethinkdbdash'
import Reconsider from 'reconsider' // or `const Reconsider = require('reconsider').default`

const db = 'my_database'
const r = rethinkdb({ host: 'localhost', db })
const recon = new Reconsider(r, { db })

Migrating up or down is as simple as calling the migrateUp() or migrateDown() method of the Reconsider instance. Both these methods will return a promise that resolves to an array of operation info objects, each one of them containing an id and an elapsed property. When migrating up, Reconsider will attempt to run all pending migrations found in the migrations/ directory of the current process by default. When migrating down, Reconsider will revert all migrations stored in the _reconsider_migration table. Once a migration has been run successfully, it will not be run again on subsequent invocations of the migrateUp method, unless it has been reverted via migrateDown().

// Run all pending migrations
recon.migrateUp().then((ops) => console.dir(ops))

// Or, if you're using babel
const ops = await recon.migrateUp()

// ops will be something like this
[{
  id: '001-create-tables',  // id of the migration
  elapsed: 7.597834  // Time it took for the migration to complete (in seconds)
}, {
  id: '002-add-initial-values',
  elapsed: 0.0123168
}]

Configuration Options

Currently, the config object passed into the Reconsider constructor supports the following properties:

Property Default Description
db Database name (required)
sourceDir migrations/ Directory containing the migrations
tableName _reconsider_migration Database table containing information about previously run migrations
logLevel info Minimum log level

Error Handling

Reconsider does not catch any errors on purpose, it is the caller's responsibility to handle errors appropriately. The basic reason for this is that handling migration errors would either involve too much guesswork or introduce a host of new config options for no good reason (Revert everything? Don't revert anything? Attempt to call the failed migration's down method?).

recon.migrateUp()
  .then((ops) => console.dir(ops))
  .catch((err) => {
    // Handle error here
  })

One consequence of Reconsider's lack of error catching is that an error in any migration will prevent all subsequent migrations from running. This, too, is intended behavior, since database migrations will more often than not rely on changes introduced by previous migrations. Since no automatic rollback is performed, and since all successful migrations will still register, migrateUp and migrateDown can safely be called again once the problem has been resolved.

This should also encourage the user to write small migrations that change one thing at a time, as opposed to huge migration files with several chained .thens.

Logging

Reconsider will output various messages to stdout by default, using console.log, console.info and console.warn as appropriate. All output is categorized into one of the following log levels: debug, verbose, info, warn, error. Minimum log level can be set via the logLevel config option.

// Use built in logger, don't output anything below "info" level (default config)
const recon = new Reconsider(r, {
  db: 'my_database',
  logLevel: 'info'
})

// Disable logging
const recon = new Reconsider(r, { db: 'my_database' }, false)

Alternatively, you can provide a custom logger implementation, e.g. an instance of winston or similar. When doing so, the provided object must implement methods for all supported log levels. Note that setting a logLevel via the config object will have no effect in this case, since Reconsider will assume that your logger has already been configured appropriately.

// Provide custom logger implementation
const myLoggerInstance = getLoggerInstanceSomehow()
const recon = new Reconsider(r, { db: 'my_database' }, myLoggerInstance)

Helpers

As of version 1.1.0, Reconsider includes a small set of helper functions meant to simplify and automate common database migration tasks, namely creating tables or indices. Each of these functions will return a database migration object, i.e. an object exposing up and down methods, which can then be exported by the migration file.

createTablesMigration

This function will return a migration that will create tables when migrating up and drop these tables when migrating down. createTablesMigration expects an array of table names.

// In file migrations/xx-create-tables.js
const { helpers } = require('reconsider')

module.exports = helpers.createTablesMigration([ 'first_table', 'second_table' ])

createIndexMigration

This function will return a migration that will create indices when migrating up and drop these indices when migrating down. createIndexMigration expects an array of index specifications. Each index specification is an object containing a table and an index property, and optionally an options object and/or a spec function. An options object can be anything that r.indexCreate() accepts, while the spec property must be a function that returns an index definition (which, again, can be anything that r.indexCreate() accepts). spec will be passed the rethinkdbdash instance when it is executed.

// In file migrations/xx-create-indices.js
const { helpers } = require('reconsider')
const table = 'first_table'

module.exports = helpers.createIndexMigration([
    { table, index: 'someProp' }, // Simple index
    { table, index: 'compoundIndex', spec: (r) => [ r.row('firstProp'), r.row('secondProp') ] }, // Compound index
    { table, index: 'geoProp', options: { geo: true } }, // Geo index
    { table, index: 'multiIndex', options: { multi: true } }, // Multi index
    { table, index: 'arbitraryExpr', spec: (r) => (doc) => r.branch(doc.hasFields('foo'), doc('foo'), doc('bar')) } // Index based on an arbitrary expression
])

Testing

A simple Vagrant VM running a RethinkDB server has been included in the test/misc folder.

npm run test

API Docs

Official API documentation lives here.

Author

Michael Smesnik

License

MIT