oracle-async

Overview

This library has a few core principles:

• Focus on promises and async iterators, do away with callbacks and event-emitting streams
• Make advanced usage optional but easy, e.g.:
  • transactions
  • streaming large result sets
  • prepared statements
• Make it difficult to make a mistake, e.g.:
  • Always use a connection pool
  • Hide everything having to do with acquiring/releasing connections

Getting Started

Standard connection

A Db instance represents a connection pool, and a possible set of replica pools to be used for fallback in the event the primary pool's instance is down. You will want to make a single reference to this object and export it so that it can be imported all over your code.

import Db from 'oracle-async'
export const db = new Db({
  // You may provide connectString: string, as in oracledb's PoolAttributes property, or you may provide the
  // following elements to have this library build a properly formatted Easy-Connect string for you:
  server: 'yourhost',
  port: 1521,
  service: 'xe',
  user: 'test-api', // Also configurable via environment variable.
  password: 'somepassword', // Also configurable via environment variable.

  // lowerCaseColumns determines if row objects will be converted to lowercase keys.
  lowerCaseColumns: true,
  // connectTimeout allows you to specify the number of seconds to wait before timing out connection attempts.
  connectTimeout: 5, // Optional. Default=15, also configurable in environment variable.
  // onStatus is a callback definition to define extra actions on status changes.
  onStatus: (status) => { console.log(status) },
  replicas: [{
    // connectString can be provided for each fallback pool here as well or, if you prefer the string 
    // to be built for you, then you can supply the following three parts for each pool to build with.
    server: 'fallback-host',
    port: 1521,
    service: 'xe-replica',
    // Same as optional connectTimeout above but in context to this replica pool.
    connectTimeout: 5,
    user: 'someuser', // Also configurable via environment variable.
    password: 'somepassword' // Also configurable via environment variable.
  }]
  ... // The rest of the options include those inherited from oracledb.PoolAttributes but not referenced above.
})

async function main() {
  const row = await db.getrow('SELECT ...')
}
main().catch(e => console.error(e))

Connect with environment variables

When working in docker, it's common to keep database configuration in environment variables. In order to make that easy, this library provides a convenient way to import singleton pool attributes created with the following environment variables:

  ORACLE_HOST= #(default 'oracle')
  ORACLE_PORT= #(default '1521')
  ORACLE_SERVICE= #(default 'xe')
  ORACLE_CONNECT_STRING= #(specify the primary connect string or build with the above)
  ORACLE_CONNECT_TIMEOUT= #(default 15)
  ORACLE_USER= # (default 'system')
  ORACLE_PASS= # (specify in override)

  # The following are provided for a singleton connection pool configuration of a single replica instance. Additional
  # replica configs can be passed through the oracle-async.PoolOptions config object passed to the Db constructor but for 
  # simpler environment variable driven setup the following replica environment variables are supported.
  ORACLE_REPLICA_HOST= # (defaults to primary pool's host)
  ORACLE_REPLICA_PORT= # (defaults to primary pool's port)
  ORACLE_REPLICA_SERVICE= # (will not use above replica environment variables if not defined)
  ORACLE_REPLICA_CONNECT_STRING= # (specify the replica connect string, or build with the above, or default to primary)
  ORACLE_REPLICA_CONNECT_TIMEOUT= # (defaults to primary pool's timeout)
  ORACLE_REPLICA_USER= # (defaults to primary pool's user)
  ORACLE_REPLICA_PASS= # (specify in override - defaults to primary pool's password)

  # In addition to the above, the following will be applied to all pools if configured. This can be overridden for 
  # replicas if the Db constructor is passed a PoolOptions config that specifies otherwise for any replicas with
  # configuration deviations that are diresired.

  UV_THREADPOOL_SIZE= # (default 4)
  # This controls both the number of threads oracle client starts up with and max connections
  # in the pool, which should match unless you have multiple pools/database servers.
  # In that case, you should set ORACLE_POOL_SIZE to something smaller, and then make sure your
  # pools' max connections all add up to UV_THREADPOOL_SIZE or less

  ORACLE_LOWERCASE= #('true')
  # If this is truthy, row objects will have lowercase keys instead of uppercase, just a quality
  # of life thing. You can also set this as a default at runtime with `db.setQueryOptions({ lowerCaseColumns: true })`

This way, connecting is very simple, and you don't have to worry about creating a singleton pool for the rest of your codebase to import:

import db from 'oracle-async/db'

async function main() {
  const row = await db.getrow('SELECT ...')
}
main().catch(e => console.error(e))

CommonJS imports

You must refer to .default when importing with require:

const db = require('oracle-async/db').default // or
const { default: db } = require('oracle-async/db') // or
const Db = require('oracle-async').default // or
const { default: Db } = require('oracle-async')

Basic Usage

A lot of convenience methods are provided that allow you to specify the kind of operation you are about to do and the kind of return data you expect.

Querying

const rows = await db.getall('SELECT name FROM mytable')
console.log(rows) // [{ name: 'John' }, { name: 'Maria' }, ...]
const row = await db.getrow('SELECT name FROM mytable WHERE name=:name', { name: 'John' })
console.log(row) // { name: 'John' }
const name = await db.getval('SELECT name FROM mytable WHERE name=:name', { name: 'John' })
console.log(name) // John
const names = await db.getvals('SELECT name FROM mytable WHERE name IN (:name1, :name2)',
  { name1: 'John', name2: 'Maria' })
console.log(names) // ['John', 'Maria']
const rows = await db.getallArray('SELECT name FROM mytable')
// returns rows as array instead of object, improves performance on huge datasets
console.log(rows) // [['John'],['Maria']]

Mutating

// Oracle cannot automatically determine the id column; it needs a RETURN...INTO instruction.
// If you provide the column name as an option, `RETURN ${options.insertId} INTO :insertid`
// will be added to the query for you.
// You can also add your own RETURN ... INTO :insertid
// If you do neither, db.insert will simply return 0
const insertId = await db.insert('INSERT INTO mytable (name) VALUES (:name)', { name: 'Mike' }, { insertId: 'id' })
const rowsUpdated = await db.update('UPDATE mytable SET name=:newname WHERE name=:oldname', { newname: 'Johnny', oldname: 'John' })
const success = await db.execute('CREATE TABLE anothertable ...')

Raw Query

If the convenience methods are hiding something you need from oracle, you can use .query() to get back whatever would have been returned by oracle.

const result = await db.query('INSERT INTO mytable (name) VALUES (:name); UPDATE anothertable SET col1=:col1', { name: 'Mike', col1: 'Value' })
const rowsUpdated = result.rowsAffected

Additionally, if you want custom transactional raw query support, or want to implement preparred statements handling you can use .queryWithConn() to execute the query with a direct reference to the connection to execute with.

const pool = await db.rawpool()
const conn = await pool.getConnection()
const result = await db.queryWithConn(conn,'UPDATE mytable SET processed=false')
const rowsUpdated = result.rowsAffected

IN helper

Writing queries with IN operators can be a little complicated when using named parameters. A helper is provided that takes your existing bound parameters object and an array to be used for the IN. It generates the SQL while also mutating your existing bound parameters, so that you can easily use it inline.

const binds = { author: authorid }
const rows = db.getall(`
  SELECT * FROM mytable
  WHERE author = :author
  AND (
    genre IN (${db.in(binds, genres)}) OR
    title IN (${db.in(binds, titles)})
  )`, binds)

Advanced Usage

Streaming

Async Iterable

The async iterable approach is by far the simplest. It works almost exactly like .getall(), except the advantage here is that it does not load the entire result set into memory at one time, which will help you avoid out-of-memory issues when dealing with thousands or millions of rows.

const stream = db.stream('SELECT name FROM mytable')
for await (const row of stream) {
  // work on the row
}

for await is very safe, as breaking the loop or throwing an error inside the loop will clean up the stream appropriately.

Note that .stream() returns a node Readable in object mode, so you can easily do other things with it like .pipe() it to another stream processor. When using the stream without for await, you must call stream.destroy if you do not want to finish processing it and carefully use try {} finally {} to destroy it in case your code throws an error. Failure to do so will leak a connection from the pool.

Iterator .next()

Another available approach is to use the iterator pattern directly. This is a standard javascript iterator that you would receive from anything that supports the async iterator pattern. Probably to be avoided unless you are working with multiple result sets at the same time (e.g. syncing two tables).

const iterator1 = db.iterator('SELECT name FROM mytable')
const iterator2 = db.iterator('SELECT * FROM anothertable')
while (true) {
  const { value: row1, done1 } = await iterator1.next()
  const { value: row2, done2 } = await iterator2.next()
  if (!done1 || !done2) {
    try {
      // do some work to sync the rows
    } catch (e) {
      await iterator1.return()
      await iterator2.return()
      throw e
    }
  } else {
    break
  }
}

As illustrated above, an iterator needs to be cleaned up when your code is aborted before reaching the end, or it will leak a connection. Remember to await iterator.return() if you are going to abandon the iterator, and inside try/catch/finally blocks in your row processing code. An SQL query error will show up on the first await iterator.next() and does not need to be cleaned up.

streamArray

For very large datasets, you may want to avoid the work of converting rows to objects. You can use .streamArray() instead of .stream() to do so. Also see .getallArray() above.

You can access the column names by listening to the metadata event:

const stream = db.streamArray('SELECT name FROM mytable')
let colnames = []
stream.on('metadata', metadata => {
  colnames = metadata.map(md => md.name)
})
for await (const row of stream) {
  // work on row
}

Transactions

A method is provided to support working inside a transaction. Since the core Db object is an oracle pool, you cannot send transaction commands without this method, as each command would end up on a different connection.

To start a transaction, provide a callback that MUST return a promise (just make it async). A new instance of db is provided to the callback; it represents a single connection, inside a transaction. Remember to pass this along to any other functions you call during the transaction - if you call a function that uses the global db object its work will happen outside the transaction!

You do NOT send START TRANSACTION, ROLLBACK, or COMMIT as these are handled automatically.

await db.transaction(async db => {
  // both of these queries happen in the same transaction
  const row = await db.getrow('SELECT * FROM ...')
  await db.update('UPDATE mytable SET ...')
})

If you need to roll back, simply throw an error. Similarly, any query that throws an error will trigger a rollback.

await db.transaction(async db => {
  const id = await db.insert('INSERT INTO user ...')
  throw new Error('oops!')
}) // the INSERT will be rolled back and will not happen

Retrying Deadlocks

db.transaction() accepts an options parameter allowing you to set a maximum number of retries allowed upon deadlock:

await db.transaction(async db => {
  const row = await db.getrow('SELECT * FROM ...')
  await db.update('UPDATE mytable SET ...')
}, { retries: 1 })

If this transaction is the loser of a deadlock, it will retry the whole transaction once, including refetching the getrow statement.

Prepared Statements

Support for prepared statements is planned but not yet implemented. If you need it, you can access the raw Pool object with await db.rawpool() and follow the oracledb documentation.

Timezones

Working with timezones can be very confusing. Where possible you should use the TIMESTAMP WITH TIME ZONE type so that the time zone is stored alongside every date.

Typescript

This library is written in typescript and provides its own types. For added convenience, methods that return rows or values will accept a generic so that you can specify the return type you expect:

interface Book {
  id: number
  title: string
  isbn: string
}
const row = await db.getrow<Book>('SELECT id, title, isbn FROM books WHERE id=@id', { id: 5 })
// `row` is a `Book`
const rows = await db.getall<Book>('SELECT id, title, isbn FROM books')
// `rows` is a `Book[]`
const stream = db.stream<Book>('SELECT id, title, isbn FROM books')
for await (const row of stream) {
  // `row` is a `Book`
}
const insertId = await db.insert<string>('INSERT INTO mytable (name) VALUES (:name)', { name: 'Mike' }, { insertId: 'id' })
// insertId is a string (default is number)