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5.0.0 • Public • Published

MySQL Chassis

Build Status

A promise-based API for mysqljs (mysqljs is formerly called node-mysql). It provides easy SQL methods including:

It also provides a middleware layer for db.onBeforeResults and db.onResults.

Key features:

  • Promise-based layer over mysqljs
  • External SQL files
  • Named bind-parameter placeholders, similar to what PDO offers
  • Better results for SELECT ... LIMIT BY 1 (see middleware)
  • SQL templates with EJS (see middleware)
  • "Transforms Feature" to normalize JS to SQL


npm install --save mysql-chassis


Quickstart Example:

// Non-ES6
// var MySQl = require('mysql-chassis').default;
// ES6
import MySQL from 'mysql-chassis';
const db = new MySQL({
  database: 'databasename',
  user: 'username'

Note that if you don't provide password or host options, MySQL Chassis will pass an empty string as the password and mysqljs already passes localhost by default.

The options passed in are a blend of MySQL Chassis and mysqljs options. Any options that mysqljs createConnection() or createPool() can receive will be passed through. Access to the mysqljs underlying connection (pooled or un-pooled) is given as follows:

const db = new MySQL({
  database: 'databasename',
  user: 'username'
// mysqljs' connection object

MySQL Chassis Connection Options

As stated before, the options passed into MySQL Chassis are a blend of MySQL Chassis options and the underlying mysqljs library. See their connection options for more details. For MySQL Chassis, here are the options:

  • password: Even though this is a mysqljs option, we just want to note that if this is omitted, then null is sent to mysqljs.
  • sqlPath: A filepath where SQL files can be found. This is used by selectFile() and queryFile(). If no value is passed. Default value is ./sql
  • retryLimit: How many times should MySQL Chassis try to re-connect if a connection is not made initially, or if a connection is lost. Default value is Infinity
  • transforms: An object for transform settings. See Transforms below.

Example Connection

Here's a more elaborate example of what your connection to MySQL Chassis might look like

import MySQL from 'mysql-chassis';
import path from 'path';
const db = new MySQL({
  host: process.env.DB_HOST,
  database: process.env.DB_NAME,
  user: process.env.DB_USER,
  password: process.env.DB_PASS,
  sqlPath: path.join(process.cwd(), './sql')
db.on('connectionAttempt', tries => {
  console.log(`MySQL Chassis: Trying to connect. Try: ${tries}`)
db.on('connectionSuccess', tries => {
  console.log(`MySQL Chassis: Connection Success. Try: ${tries}`)
db.on('connectionError', err => {
  console.error('MySQL Chassis: Could not establish connection. Code:', err.code)
db.on('connectionLost', err => {
  console.error('MySQL Chassis: Connection was lost. Code:', err.code)
db.on('connectionTriesLimitReached', tries => {
  console.error(`MySQL Chassis: Quit trying to connect after ${tries} tries`)
db.on('sqlError', err => {
  console.error(`MySQL Chassis: SQL Error`, { SQL: err.sql, Code: err.code })
// SELECT a user
const userId = 1
db.selectFile('SELECT * FROM user WHERE user_id = :userId LIMIT 1', { userId })
  .then(row => console.log(row))
  .catch(err => console.error(err));
export default db;

See the .queryFile() and .selectFile() method below for an example of how to use SQL statements as files instead of inline strings.


All query execution methods return a promise with the results of the SQL:

db.query('SELECT * FROM user').then(function(results) {
}).catch(err => {

When a SELECT statement is passed in, the results will contain the following properties:

  • rows: The same data that mysqljs would give you
  • fields: The same data that mysqljs would give you
  • sql: The SQL which was executed.

For non-SELECT statements, the results returned will be the same as mysqljs results which can contain any of the following properties depending on what type of SQL was performed:

  • affectedRows
  • insertId
  • changedRows
  • fieldCount
  • serverStatus
  • warningCount
  • message

In addition to these, there will also be a sql property returned in the results. The purpose of returning the SQL statement in the results is mostly for debugging. Many of the methods below allow you to do PDO-Style bound parameters, and some methods will even write your SQL for you if you choose to use those features. So it's nice to know what eventual SQL was executed.


If there's an error, the promise .catch(err) will give you:

  • err: The error provided by mysqljs
  • sql: The SQL which was executed

API Methods

db.query(sql, [bindValues])

query() can be used to execute any type of SQL. If the query is an SELECT statement, you can access the rows returned via result.rows:

db.query('SELECT * FROM user')
  .then(result => console.log(result.rows));

If you need to pass dynamic values into your query, use the bindValues option which will properly escape the values with mysqljs's connection.escape() method.

const bindValues = { id: 1 };
db.query('SELECT * FROM user WHERE user_id = :id', bindValues);

When you use the bindValues option, you'll also use placeholders in your SQL (such as :id) to map where the values should be placed.

db.queryFile(filename, [bindValues])

Works just like query() except it allows you to pass a filename instead of SQL directly. The filename will be appended to your sqlPath settings (configured at the time of connection, see above)

As an example:

const bindValues = { id: 1 };
db.queryFile('somefile', bindValues);

This assumes somefile.sql exists in the sqlPath folder and looks like this:

SELECT * FROM user WHERE user_id = :id

If the file exists, .queryFile() will behave exactly like .query()

Also, if you want to organize your SQL files into sub folders of the sqlPath, you can access those files as:

const bindValues = { id: 1 };
db.queryFile('path/to/somefile', bindValues)

path/to in this case is relative to the path supplied by sqlPath.

Note that the filename can written with or without the .sql extension. If no extension is provided, then .sql will be added to your filename.

db.select(sql, [bindValues])

Works just like .query() except it will return only the rows from the promise instead of a results object that contains rows with other meta data. Also it's only meant to be used on SELECT statements.

Use .select() over .query() if

  • You are running a SELECT statement, and
  • You don't care about the extra meta data returned from .query()

As a proof of concept, these two method calls would output the same data for rows:

db.select('SELECT * FROM user')
  .then(rows => console.log(rows))
db.query('SELECT * FROM user')
  .then(results => console.log(results.rows))

db.selectFile(filename, [bindValues])

Works just like .queryFile() in the sense that you can pass a filename in, but works like .select() in the sense of how it returns rows instead of results.

db.selectWhere(fields, table, whereClause)

Creates a SELECT ${fields} FROM ${table} ${where} statement and runs it through .select()

  • fields: Can be a comma delimited string or an array of strings. Either way, the fields will be normalized with backticks (in case you have any MySQL reserved words) and trimmed of whitespace.
  • table: Must be a string.
  • where: (optional) Uses .sqlWhere() to build a WHERE. See docs below for more on .sqlWhere().

db.insert(tableName, insertValues)

This method will write your INSERT statement for you and then return the results of .query(). Here's how we can execute an INSERT statement for a user with name and email fields:

const insertValues = {name: 'Brad', email: 'brad@foobar.com'};
db.insert('user', insertValues)
  .then(results => console.log(results.insertId));

The INSERT statement executed would be:

SET `name` = 'Brad'`email` = 'brad@foobar.com'

db.insertMultiple(tableName, values, columnTemplate)

Allows multiple inserts to be performed in one SQL statement (better for performance than looping and creating individual inserts when many are needed). Similar to:

INSERT INTO `some_table`
  (col1, col2, col3)
  • table: Must be a string.
  • values: Must be an array of objects, where each object represents the column name and values to be inserted into a new row. Note that the order of the properties in values does not determine their placement in the SQL statement. The order that is used in the SQL statement depends on columnTemplate and the algorithm will map the keys of the values objects to the columnTemplate.
  • columnTemplate: (optional) Must be an array of unique column names. This will be used as the "columns" section of the SQL statement. If not provided, this method will use the fields of the first object in values to make the columnTemplate

Here's an example:

const insertValues = [
  { datetime_added: 'NOW()', first_name: 'Brad' },
  { first_name: 'Dave', last_name: 'Smith', datetime_added: 'NOW()' }
db.insertMultiple('user', insertValues, ['first_name', 'last_name', 'datetime_added'])
  .then(response => console.log(response))
  .catch(err => console.log(err));

As you can see, the "uniformity" of the two objects for values do not match. That is okay in this case because we provided the last argument, an array indicating which columns we want. However, without that array, we would not get the desired result since the first object's keys datetime_added and first_name would be used as the column template, and therefore leaving the first_name out of the second insert. So always provide the third columnTemplate argument if you can.

db.update(tableName, updateValues, whereClause)

This method will write your UPDATE statement for you and then return the results of .query(). Here's how we can execute an UPDATE statement for a user to update name and email fields:

const updateValues = { name: 'Brad', email: 'brad@foobar.com' };
const whereClause = { user_id: 1, active: true };
db.update('user', updateValues, whereClause).then(function(results) {

The UPDATE statement executed would be:

SET `name` = 'Brad'`email` = 'brad@foobar.com'
WHERE `user_id` = 1
AND `active` = true

See more on .where() below.

db.insertIgnore(tableName, insertValues)

Same as .insert(), but if they primary key already exists, then the INSERT will be ignored. This will not produce an error or warning.

This relies on MySQL's INSERT IGNORE feature.

db.insertUpdate(tableName, values)

Attempt an INSERT statement, but of the primary key already exists and therefore the record cannot be inserted, then switch to an UPDATE statement.

This relies on MySQL's ON DUPLICATE KEY UPDATE feature.

db.delete(tableName, whereClause)

This method will write your DELETE statement for you and returns the same promise as query().

const whereClause = { user_id: 1, active: true };
db.delete('user', whereClause)
  .then(results => console.log(results.affectedRows));

The DELETE statement executed would be:

WHERE `user_id` = 1
AND `active` = true

See more on .sqlWhere() below.


This method is normally used by other API methods, such as .update(), and .delete(). You can also use it directly:

  user_id: 1
  active: true
})) // outputs: WHERE `user_id` = 1 AND `active` = true

Values passed in will be escaped using mysqljs's connection.escape() method.

If a string is passed in, the string will be returned without changes and without escaping. This allows you to write custom "where-clauses" as needed:

db.update('user', updateValues, 'WHERE user.datetime_added < NOW()');


For custom functionality, you can add middleware to be ran before or after queries are executed:

db.onBeforeQuery((sql, bindValues) => {
  // Here you can modify the SQL before it is ran
  return sql;
db.onResults((sql, results) => {
  // Here you can modify the results before they are returned
  return results;

Middleware Examples

Example 1: mysqljs always returns an array of rows regardless of how many rows are returned. But if you wanted to modify the results such that when the SELECT statement has a LIMIT 1 at the end, then it will just return an object for the one row, then this is how that could be done:

db.onResults((sql, results) => {
  if (results.length !== 1) return results;
  return /^SELECT\s(.|\n)+LIMIT 1$/g.test(sql.trim()) ? results[0] : results;

Example 2: If you feel inclined to treat your SQL files as templates which can be dynamic depending on the bindValues, you can use middleware with ejs templates

db.onBeforeQuery((sql, bindValues) => {
  sql = ejs.compile(sql)(bindValues);
  return sql;

Now, your SQL statements can be written as follows:

# file.sql 
FROM user
WHERE user_id = :id
<% if (active) { %>
  AND active = true
<% } %>

Now, running the following will result in the AND active = true part of the SQL running

db.select('file', { id: 1, active: true });


Transforms are a means of helping .insert() and .update() methods know what to do when then encounter values that won't go well with MySQL. The transforms object is a map of values that .insert() and .update() could encounter, and what real values we'd rather use in the creation of the SQL statement.

The default transforms are:

transforms: {
  undefined: 'NULL',
  '': 'NULL',
  'NOW()': 'NOW()',

As an example, let's say we pass undefined or an empty string into our .insert() method:

db.insert('user', { name: '', email: undefined });

Ideally for MySQL, you would want those values transformed to MySQL's NULL

# With Transforms (ideal) 
SET `name` = NULL`email` = NULL
# Without Transforms (not ideal) 
SET `name` = ''`email` = ''

Note that escaping does not occur on transformed values. The value of the transform is placed directly inside the SQL statement whenever a bindValues value matches a transform key.

As another example, let's say you want to be able to pass the NOW() or CURTIME() MySQL functions as values into your .insert() or .update() methods. As you can see, the transforms allow you to write:

db.insert('user', {name: 'Brad', datetime_added: 'NOW()'});

Which will result in:

# With Transforms (ideal) 
SET `name` = 'Brad'`datetime_added` = NOW()
# Without Transforms (will cause an error if datetime_added expects a valid date) 
SET `name` = 'Brad'`datetime_added` = 'NOW()'

Custom Transforms

You can modify the default transforms or add your own at connection time:

const db = new MySQL({
  database: 'databasename',
  user: 'username',
  transforms: {
    'lookForThisValue': 'replaceWithThisValue', // Custom
    '': 'Empty Value' // Override default



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