A wrapper for mysql2 to add convenience, especially when developing with async/await and async iterables.
npm install mysql2-asyncjavascript
import Db from 'mysql2-async'
export const db = new Db({
host: 'yourhost',
...
})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 a pool instance that has already been
created and configured with the following environment variables:
MYSQL_HOST (default 'localhost')
MYSQL_PORT (default '3306')
MYSQL_DATABASE (default 'default_database')
MYSQL_USER (default 'root')
MYSQL_PASS
MYSQL_POOL_SIZE (default is mysql2's default)
MYSQL_SKIPTZFIX (default false) // see below discussion of the timezone fix
This way, connecting is very simple, and you don't have to worry about creating and exporting the pool for the
rest of your codebase:
javascript
import db from 'mysql2-async/db'async function main() {
const row = await db.getrow('SELECT ...')
}
main().catch(e => console.error(e))
`CommonJS imports
You must refer to when importing with require:
`javascript
const Db = require('mysql2-async').default
// or the instance created with environment variables (see above)
const db = require('mysql2-async/db').default
`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
javascript
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=?', ['John'])
console.log(row) // { name: 'John' }
const name = await db.getval('SELECT name FROM mytable WHERE 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']
`
Named parameters
As you can see in the example in the previous section, mysql2's named parameter support works
here as well.
Mutating
`javascript
const insertId = await db.insert('INSERT INTO mytable (name) VALUES (?)', ['Mike'])
const rowsAffected = await db.update('UPDATE mytable SET name=? WHERE name=?', ['Johnny', 'John'])
const success = await db.execute('CREATE TABLE anothertable ...')
`
Note that returns only rows affected, not rows changed. Affected is the number of rows
that matched the WHERE, while changed is the number of rows that actually changed after the SET. I
didn't want to complicate things by trying to return both, and you can always rewrite your query like
SET val=? WHERE val!=? so that affected becomes the same as changed. And if you really don't want to,
you can use db.query to get back result.changedRows.
Raw query
If the convenience methods are hiding something you need from mysql2, you can use .query() to get
back whatever would have been returned by mysql2 (inside a promise, however).
`javascript
const result = await db.query('INSERT INTO mytable (name) VALUES (?)', ['Mike'])
const insertId = result.insertId
`
IN helper
Writing queries with operators can be a little complicated, especially when using named parameters.
A helper is provided that takes your existing bound parameters array/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.
`javascript
const binds = { author: authorid }
const rows = db.getall(, binds)
`
Advanced Usage
Streaming
$3
The async iterable approach is by far the simplest. It works almost exactly like , 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.
`javascript
const stream = db.stream('SELECT name FROM mytable')
for await (const row of stream) {
// work on the row
}
`
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.
$3
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).
`javascript
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 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.
Transactions
A method is provided to support working inside a transaction. Since the core Db object is a mysql 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.
`javascript
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.
javascript
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
`
$3
accepts an options parameter allowing you to set a maximum number of retries allowed upon deadlock:
`javascript
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 statement.Prepared Statements
Prepared statements are nearly automatic, you just need to notate which queries need it. It's desirable to
carefully pick a few complicated queries because each unique SQL string that uses prepared statement support
will use up a small amount of resources on both client and server.
`javascript
await db.getrow('SELECT m., o. FROM mytable m, othertable o WHERE ...complicated...',
[ / bind parameters / ],
{ saveAsPrepared: true }
)
`
Now, future calls with this same SQL statement (before inserting bound parameters) will be able to skip the
query planning stage on the mysql server and return data a little bit faster.Note that this is just a pass-through to mysql2's prepared statement implementation, so you can refer to
their documentation / code for more details.
Timezone Fix
Working with timezones can be very confusing. This library takes an opinionated approach and sets it up so
that all dates will be stored as UTC, whether the date is set automatically on the server through a
setting, set with a server-side function such as NOW(), or sent from the client
as a javascript Date() object.Older versions of mysql (less than 5.1) may throw an error because of this. If you need to work with a server
running an old version of mysql, or an existing database that does not or has not stored dates as UTC in the past,
you may set the
skiptzfix configuration variable and then be very careful while handling dates.
`javascript
const db = new Db({ skiptzfix: true })
`Closing the Pool / Graceful Shutdown
Generally, closing the pool is optional, as killing the node instance will close connections automatically. However,
you may want to avoid - as a way of ensuring you have identified all sources of open handles in your
code.If you are running a script, then you can call
await db.end().If you are running a server (HTTP or otherwise), listen for sigint/sigterm and close your server first, so that any
existing requests can be finished. If you end this database pool too early, those existing requests may fail.
Your server shutdown code would look something like:
`javascript
async function shutdown () {
await server.close()
await db.end()
}
process.on('SIGTERM', shutdown)
process.on('SIGINT', shutdown)
`If you've successfully closed all open connections and emptied the node event loop, the process should exit on
its own. If not, you may have missed something that's still running, like a network connection, setInterval, or
setTimeout loop.
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:
typescript
interface Book {
id: number
title: string
isbn: string
}
const row = await db.getrow('SELECT id, title, isbn FROM books WHERE id=?', [5])
// row is a Book
const rows = await db.getall('SELECT id, title, isbn FROM books')
// is a Book[]
const stream = db.stream('SELECT id, title, isbn FROM books')
for await (const row of stream) {
// is a Book
}