postgres

What is postgres?

The 'postgres' npm package is a modern, high-performance PostgreSQL client for Node.js. It provides a simple and efficient way to interact with PostgreSQL databases, supporting both basic and advanced database operations.

What are postgres's main functionalities?

Connecting to a Database

This feature allows you to establish a connection to a PostgreSQL database using a connection string.

const postgres = require('postgres');
const sql = postgres('postgres://username:password@localhost:5432/mydatabase');

Executing Queries

You can execute SQL queries using tagged template literals, which helps in preventing SQL injection attacks.

const result = await sql`SELECT * FROM users WHERE id = ${userId}`;

Parameterized Queries

This feature allows you to use parameterized queries to safely pass variables into your SQL statements.

const result = await sql`SELECT * FROM users WHERE age > ${age}`;

Transactions

You can perform multiple database operations within a transaction to ensure atomicity.

await sql.begin(async sql => {
  await sql`INSERT INTO users (name) VALUES (${name})`;
  await sql`INSERT INTO profiles (user_id, bio) VALUES (${userId}, ${bio})`;
});

Connection Pooling

The package supports connection pooling to manage multiple database connections efficiently.

const sql = postgres({
  host: 'localhost',
  port: 5432,
  username: 'username',
  password: 'password',
  database: 'mydatabase',
  max: 10 // maximum number of connections in the pool
});

Other packages similar to postgres

pg

The 'pg' package is the official PostgreSQL client for Node.js. It is widely used and provides a comprehensive set of features for interacting with PostgreSQL databases. Compared to 'postgres', 'pg' is more mature and has a larger community, but 'postgres' offers a more modern API and better performance in some cases.

knex

The 'knex' package is a SQL query builder for Node.js that supports multiple database engines, including PostgreSQL. It provides a flexible and powerful API for building and executing SQL queries. While 'knex' is more versatile due to its support for various databases, 'postgres' is more specialized and optimized for PostgreSQL.

sequelize

The 'sequelize' package is a promise-based ORM for Node.js that supports PostgreSQL, MySQL, SQLite, and MSSQL. It provides a higher-level abstraction for database operations, including model definitions and associations. 'sequelize' is more feature-rich and suitable for complex applications, but 'postgres' offers a simpler and more direct approach to interacting with PostgreSQL.

README

• 🚀 Fastest full-featured node & deno client
• 🏷 ES6 Tagged Template Strings at the core
• 🏄‍♀️ Simple surface API
• 🖊️ Dynamic query support
• 💬 Chat and help on Gitter
• 🐦 Follow on Twitter

Getting started

Installation

$ npm install postgres

Usage

Create your sql database instance

// db.js
import postgres from 'postgres'

const sql = postgres({ /* options */ }) // will use psql environment variables

export default sql

Simply import for use elsewhere

// users.js
import sql from './db.js'

async function getUsersOver(age) {
  const users = await sql`
    select
      name,
      age
    from users
    where age > ${ age }
  `
  // users = Result [{ name: "Walter", age: 80 }, { name: 'Murray', age: 68 }, ...]
  return users
}


async function insertUser({ name, age }) {
  const users = await sql`
    insert into users
      (name, age)
    values
      (${ name }, ${ age })
    returning name, age
  `
  // users = Result [{ name: "Murray", age: 68 }]
  return users
}

ESM dynamic imports

The library can be used with ESM dynamic imports as well as shown here.

const { default: postgres } = await import('postgres')

Table of Contents

• Connection
• Queries
• Building queries
• Advanced query methods
• Transactions
• Data Transformation
• Listen & notify
• Realtime subscribe
• Numbers, bigint, numeric
• Result Array
• Connection details
• Custom Types
• Teardown / Cleanup
• Error handling
• TypeScript support
• Reserving connections
• Changelog

Connection

postgres([url], [options])

You can use either a postgres:// url connection string or the options to define your database connection properties. Options in the object will override any present in the url. Options will fall back to the same environment variables as psql.

const sql = postgres('postgres://username:password@host:port/database', {
  host                 : '',            // Postgres ip address[s] or domain name[s]
  port                 : 5432,          // Postgres server port[s]
  database             : '',            // Name of database to connect to
  username             : '',            // Username of database user
  password             : '',            // Password of database user
  ...and more
})

More options can be found in the Connection details section.

Queries

await sql`...` -> Result[]

Postgres.js utilizes Tagged template functions to process query parameters before interpolation. Using tagged template literals benefits developers by:

1. Enforcing safe query generation
2. Giving the sql`` function powerful utility and query building features.

Any generic value will be serialized according to an inferred type, and replaced by a PostgreSQL protocol placeholder $1, $2, .... The parameters are then sent separately to the database which handles escaping & casting.

All queries will return a Result array, with objects mapping column names to each row.

const xs = await sql`
  insert into users (
    name, age
  ) values (
    'Murray', 68
  )

  returning *
`

// xs = [{ user_id: 1, name: 'Murray', age: 68 }]

Please note that queries are first executed when awaited – or instantly by using .execute().

Query parameters

Parameters are automatically extracted and handled by the database so that SQL injection isn't possible. No special handling is necessary, simply use tagged template literals as usual.

const name = 'Mur'
    , age = 60

const users = await sql`
  select
    name,
    age
  from users
  where
    name like ${ name + '%' }
    and age > ${ age }
`
// users = [{ name: 'Murray', age: 68 }]

Be careful with quotation marks here. Because Postgres infers column types, you do not need to wrap your interpolated parameters in quotes like '${name}'. This will cause an error because the tagged template replaces ${name} with $1 in the query string, leaving Postgres to do the interpolation. If you wrap that in a string, Postgres will see '$1' and interpret it as a string as opposed to a parameter.

Dynamic column selection

const columns = ['name', 'age']

await sql`
  select
    ${ sql(columns) }
  from users
`

// Which results in:
select "name", "age" from users

Dynamic inserts

const user = {
  name: 'Murray',
  age: 68
}

await sql`
  insert into users ${
    sql(user, 'name', 'age')
  }
`

// Which results in:
insert into users ("name", "age") values ($1, $2)

// The columns can also be given with an array
const columns = ['name', 'age']

await sql`
  insert into users ${
    sql(user, columns)
  }
`

You can omit column names and simply execute sql(user) to get all the fields from the object as columns. Be careful not to allow users to supply columns that you do not want to be inserted.

Multiple inserts in one query

If you need to insert multiple rows at the same time it's also much faster to do it with a single insert. Simply pass an array of objects to sql().

const users = [{
  name: 'Murray',
  age: 68,
  garbage: 'ignore'
},
{
  name: 'Walter',
  age: 80
}]

await sql`insert into users ${ sql(users, 'name', 'age') }`

// Is translated to:
insert into users ("name", "age") values ($1, $2), ($3, $4)

// Here you can also omit column names which will use object keys as columns
await sql`insert into users ${ sql(users) }`

// Which results in:
insert into users ("name", "age") values ($1, $2), ($3, $4)

Dynamic columns in updates

This is also useful for update queries

const user = {
  id: 1,
  name: 'Murray',
  age: 68
}

await sql`
  update users set ${
    sql(user, 'name', 'age')
  }
  where user_id = ${ user.id }
`

// Which results in:
update users set "name" = $1, "age" = $2 where user_id = $3

// The columns can also be given with an array
const columns = ['name', 'age']

await sql`
  update users set ${
    sql(user, columns)
  }
  where user_id = ${ user.id }
`

Multiple updates in one query

To create multiple updates in a single query, it is necessary to use arrays instead of objects to ensure that the order of the items correspond with the column names.

const users = [
  [1, 'John', 34],
  [2, 'Jane', 27],
]

await sql`
  update users set name = update_data.name, age = (update_data.age)::int
  from (values ${sql(users)}) as update_data (id, name, age)
  where users.id = (update_data.id)::int
  returning users.id, users.name, users.age
`

Dynamic values and where in

Value lists can also be created dynamically, making where in queries simple too.

const users = await sql`
  select
    *
  from users
  where age in ${ sql([68, 75, 23]) }
`

or

const [{ a, b, c }] = await sql`
  select
    *
  from (values ${ sql(['a', 'b', 'c']) }) as x(a, b, c)
`

Building queries

Postgres.js features a simple dynamic query builder by conditionally appending/omitting query fragments. It works by nesting sql`` fragments within other sql`` calls or fragments. This allows you to build dynamic queries safely without risking sql injections through usual string concatenation.

Partial queries

const olderThan = x => sql`and age > ${ x }`

const filterAge = true

await sql`
  select
   *
  from users
  where name is not null ${
    filterAge
      ? olderThan(50)
      : sql``
  }
`
// Which results in:
select * from users where name is not null
// Or
select * from users where name is not null and age > 50

Dynamic filters

await sql`
  select
    *
  from users ${
    id
      ? sql`where user_id = ${ id }`
      : sql``
  }
`

// Which results in:
select * from users
// Or
select * from users where user_id = $1

SQL functions

Using keywords or calling functions dynamically is also possible by using sql`` fragments.

const date = null

await sql`
  update users set updated_at = ${ date || sql`now()` }
`

// Which results in:
update users set updated_at = now()

Table names

Dynamic identifiers like table names and column names is also supported like so:

const table = 'users'
    , column = 'id'

await sql`
  select ${ sql(column) } from ${ sql(table) }
`

// Which results in:
select "id" from "users"

Quick primer on interpolation

Here's a quick oversight over all the ways to do interpolation in a query template string:

Interpolation syntax	Usage	Example
${ sql`` }	for keywords or sql fragments	await sql`SELECT * FROM users ${sql`order by age desc` }`
${ sql(string) }	for identifiers	await sql`SELECT * FROM ${sql('table_name')`
${ sql([] or {}, ...) }	for helpers	await sql`INSERT INTO users ${sql({ name: 'Peter'})}`
${ 'somevalue' }	for values	await sql`SELECT * FROM users WHERE age = ${42}`

Advanced query methods

Cursors

await sql``.cursor([rows = 1], [fn])

Use cursors if you need to throttle the amount of rows being returned from a query. You can use a cursor either as an async iterable or with a callback function. For a callback function new results won't be requested until the promise / async callback function has resolved.

callback function

await sql`
  select
    *
  from generate_series(1,4) as x
`.cursor(async([row]) => {
  // row = { x: 1 }
  await http.request('https://example.com/wat', { row })
})

for await...of

// for await...of
const cursor = sql`select * from generate_series(1,4) as x`.cursor()

for await (const [row] of cursor) {
  // row = { x: 1 }
  await http.request('https://example.com/wat', { row })
}

A single row will be returned by default, but you can also request batches by setting the number of rows desired in each batch as the first argument to .cursor:

await sql`
  select
    *
  from generate_series(1,1000) as x
`.cursor(10, async rows => {
  // rows = [{ x: 1 }, { x: 2 }, ... ]
  await Promise.all(rows.map(row =>
    http.request('https://example.com/wat', { row })
  ))
})

If an error is thrown inside the callback function no more rows will be requested and the outer promise will reject with the thrown error.

You can close the cursor early either by calling break in the for await...of loop, or by returning the token sql.CLOSE from the callback function.

await sql`
  select * from generate_series(1,1000) as x
`.cursor(row => {
  return Math.random() > 0.9 && sql.CLOSE // or sql.END
})

Instant iteration

await sql``.forEach(fn)

If you want to handle rows returned by a query one by one, you can use .forEach which returns a promise that resolves once there are no more rows.

await sql`
  select created_at, name from events
`.forEach(row => {
  // row = { created_at: '2019-11-22T14:22:00Z', name: 'connected' }
})

// No more rows

Query Descriptions

await sql``.describe() -> Result[]

Rather than executing a given query, .describe will return information utilized in the query process. This information can include the query identifier, column types, etc.

This is useful for debugging and analyzing your Postgres queries. Furthermore, .describe will give you access to the final generated query string that would be executed.

Rows as Array of Values

sql``.values()

Using .values will return rows as an array of values for each column, instead of objects.

This can be useful to receive identically named columns, or for specific performance/transformation reasons. The column definitions are still included on the result array, plus access to parsers for each column.

Rows as Raw Array of Buffers

sql``.raw()

Using .raw will return rows as an array with Buffer values for each column, instead of objects.

This can be useful for specific performance/transformation reasons. The column definitions are still included on the result array, plus access to parsers for each column.

Queries in Files

await sql.file(path, [args], [options]) -> Result[]

Using a file for a query is also supported with optional parameters to use if the file includes $1, $2, etc

const result = await sql.file('query.sql', ['Murray', 68])

Multiple statements in one query

await sql``.simple()

The postgres wire protocol supports "simple" and "extended" queries. "simple" queries supports multiple statements, but does not support any dynamic parameters. "extended" queries support parameters but only one statement. To use "simple" queries you can use sql``.simple(). That will create it as a simple query.

await sql`select 1; select 2;`.simple()

Copy to/from as Streams

Postgres.js supports COPY ... queries, which are exposed as Node.js streams.

await sql`copy ... from stdin`.writable() -> Writable

import { pipeline } from 'node:stream/promises'

// Stream of users with the default tab delimitated cells and new-line delimitated rows
const userStream = Readable.from([
  'Murray\t68\n',
  'Walter\t80\n'
])

const query = await sql`copy users (name, age) from stdin`.writable()
await pipeline(userStream, query);

await sql`copy ... to stdout`.readable() -> Readable

Using Stream Pipeline

import { pipeline } from 'node:stream/promises'
import { createWriteStream } from 'node:fs'

const readableStream = await sql`copy users (name, age) to stdout`.readable()
await pipeline(readableStream, createWriteStream('output.tsv'))
// output.tsv content: `Murray\t68\nWalter\t80\n`

Using for await...of

const readableStream = await sql`
  copy (
    select name, age
    from users
    where age = 68
  ) to stdout
`.readable()
for await (const chunk of readableStream) {
  // chunk.toString() === `Murray\t68\n`
}

NOTE This is a low-level API which does not provide any type safety. To make this work, you must match your copy query parameters correctly to your Node.js stream read or write code. Ensure Node.js stream backpressure is handled correctly to avoid memory exhaustion.

Canceling Queries in Progress

Postgres.js supports, canceling queries in progress. It works by opening a new connection with a protocol level startup message to cancel the current query running on a specific connection. That means there is no guarantee that the query will be canceled, and due to the possible race conditions it might even result in canceling another query. This is fine for long running queries, but in the case of high load and fast queries it might be better to simply ignore results instead of canceling.

const query = sql`select pg_sleep 100`.execute()
setTimeout(() => query.cancel(), 100)
const result = await query

Execute

await sql``.execute()

The lazy Promise implementation in Postgres.js is what allows it to distinguish Nested Fragments from the main outer query. This also means that queries are always executed at the earliest in the following tick. If you have a specific need to execute the query in the same tick, you can call .execute()

Unsafe raw string queries

Advanced unsafe use cases

await sql.unsafe(query, [args], [options]) -> Result[]

If you know what you're doing, you can use unsafe to pass any string you'd like to postgres. Please note that this can lead to SQL injection if you're not careful.

sql.unsafe('select ' + danger + ' from users where id = ' + dragons)

You can also nest sql.unsafe within a safe sql expression. This is useful if only part of your fraction has unsafe elements.

const triggerName = 'friend_created'
const triggerFnName = 'on_friend_created'
const eventType = 'insert'
const schema_name = 'app'
const table_name = 'friends'

await sql`
  create or replace trigger ${sql(triggerName)}
  after ${sql.unsafe(eventType)} on ${sql.unsafe(`${schema_name}.${table_name}`)}
  for each row
  execute function ${sql(triggerFnName)}()
`

await sql`
  create role friend_service with login password ${sql.unsafe(`'${password}'`)}
`

Transactions

BEGIN / COMMIT await sql.begin([options = ''], fn) -> fn()

Use sql.begin to start a new transaction. Postgres.js will reserve a connection for the transaction and supply a scoped sql instance for all transaction uses in the callback function. sql.begin will resolve with the returned value from the callback function.

BEGIN is automatically sent with the optional options, and if anything fails ROLLBACK will be called so the connection can be released and execution can continue.

const [user, account] = await sql.begin(async sql => {
  const [user] = await sql`
    insert into users (
      name
    ) values (
      'Murray'
    )
    returning *
  `

  const [account] = await sql`
    insert into accounts (
      user_id
    ) values (
      ${ user.user_id }
    )
    returning *
  `

  return [user, account]
})

Do note that you can often achieve the same result using WITH queries (Common Table Expressions) instead of using transactions.

It's also possible to pipeline the requests in a transaction if needed by returning an array with queries from the callback function like this:

const result = await sql.begin(sql => [
  sql`update ...`,
  sql`update ...`,
  sql`insert ...`
])

SAVEPOINT await sql.savepoint([name], fn) -> fn()

sql.begin('read write', async sql => {
  const [user] = await sql`
    insert into users (
      name
    ) values (
      'Murray'
    )
  `

  const [account] = (await sql.savepoint(sql =>
    sql`
      insert into accounts (
        user_id
      ) values (
        ${ user.user_id }
      )
    `
  ).catch(err => {
    // Account could not be created. ROLLBACK SAVEPOINT is called because we caught the rejection.
  })) || []

  return [user, account]
})
.then(([user, account]) => {
  // great success - COMMIT succeeded
})
.catch(() => {
  // not so good - ROLLBACK was called
})

PREPARE TRANSACTION await sql.prepare([name]) -> fn()

Indicates that the transactions should be prepared using the PREPARE TRANSACTION [NAME] statement instead of being committed.

sql.begin('read write', async sql => {
  const [user] = await sql`
    insert into users (
      name
    ) values (
      'Murray'
    )
  `

  await sql.prepare('tx1')
})

Data Transformation

Postgres.js allows for transformation of the data passed to or returned from a query by using the transform option.

Built in transformation functions are:

• For camelCase - postgres.camel, postgres.toCamel, postgres.fromCamel
• For PascalCase - postgres.pascal, postgres.toPascal, postgres.fromPascal
• For Kebab-Case - postgres.kebab, postgres.toKebab, postgres.fromKebab

These built in transformations will only convert to/from snake_case. For example, using { transform: postgres.toCamel } will convert the column names to camelCase only if the column names are in snake_case to begin with. { transform: postgres.fromCamel } will convert camelCase only to snake_case.

By default, using postgres.camel, postgres.pascal and postgres.kebab will perform a two-way transformation - both the data passed to the query and the data returned by the query will be transformed:

// Transform the column names to and from camel case
const sql = postgres({ transform: postgres.camel })

await sql`CREATE TABLE IF NOT EXISTS camel_case (a_test INTEGER, b_test TEXT)`
await sql`INSERT INTO camel_case ${ sql([{ aTest: 1, bTest: 1 }]) }`
const data = await sql`SELECT ${ sql('aTest', 'bTest') } FROM camel_case`

console.log(data) // [ { aTest: 1, bTest: '1' } ]

To only perform half of the transformation (eg. only the transformation to or from camel case), use the other transformation functions:

// Transform the column names only to camel case
// (for the results that are returned from the query)
postgres({ transform: postgres.toCamel })

await sql`CREATE TABLE IF NOT EXISTS camel_case (a_test INTEGER)`
await sql`INSERT INTO camel_case ${ sql([{ a_test: 1 }]) }`
const data = await sql`SELECT a_test FROM camel_case`

console.log(data) // [ { aTest: 1 } ]

// Transform the column names only from camel case
// (for interpolated inserts, updates, and selects)
const sql = postgres({ transform: postgres.fromCamel })

await sql`CREATE TABLE IF NOT EXISTS camel_case (a_test INTEGER)`
await sql`INSERT INTO camel_case ${ sql([{ aTest: 1 }]) }`
const data = await sql`SELECT ${ sql('aTest') } FROM camel_case`

console.log(data) // [ { a_test: 1 } ]

Note that Postgres.js does not rewrite the static parts of the tagged template strings. So to transform column names in your queries, the sql() helper must be used - eg. ${ sql('columnName') } as in the examples above.

Transform undefined Values

By default, Postgres.js will throw the error UNDEFINED_VALUE: Undefined values are not allowed when undefined values are passed

// Transform the column names to and from camel case
const sql = postgres({
  transform: {
    undefined: null
  }
})

await sql`CREATE TABLE IF NOT EXISTS transform_undefined (a_test INTEGER)`
await sql`INSERT INTO transform_undefined ${ sql([{ a_test: undefined }]) }`
const data = await sql`SELECT a_test FROM transform_undefined`

console.log(data) // [ { a_test: null } ]

To combine with the built in transform functions, spread the transform in the transform object:

// Transform the column names to and from camel case
const sql = postgres({
  transform: {
    ...postgres.camel,
    undefined: null
  }
})

await sql`CREATE TABLE IF NOT EXISTS transform_undefined (a_test INTEGER)`
await sql`INSERT INTO transform_undefined ${ sql([{ aTest: undefined }]) }`
const data = await sql`SELECT ${ sql('aTest') } FROM transform_undefined`

console.log(data) // [ { aTest: null } ]

Custom Transform Functions

To specify your own transformation functions, you can use the column, value and row options inside of transform, each an object possibly including to and from keys:

• to: The function to transform the outgoing query column name to, i.e SELECT ${ sql('aName') } to SELECT a_name when using postgres.toCamel.
• from: The function to transform the incoming query result column name to, see example below.

Both parameters are optional, if not provided, the default transformation function will be used.

// Implement your own functions, look at postgres.toCamel, etc
// as a reference:
// https://github.com/porsager/postgres/blob/4241824ffd7aa94ffb482e54ca9f585d9d0a4eea/src/types.js#L310-L328
function transformColumnToDatabase() { /* ... */ }
function transformColumnFromDatabase() { /* ... */ }

const sql = postgres({
  transform: {
    column: {
      to: transformColumnToDatabase,
      from: transformColumnFromDatabase,
    },
    value: { /* ... */ },
    row: { /* ... */ }
  }
})

Listen & notify

When you call .listen, a dedicated connection will be created to ensure that you receive notifications instantly. This connection will be used for any further calls to .listen. The connection will automatically reconnect according to a backoff reconnection pattern to not overload the database server.

Listen await sql.listen(channel, onnotify, [onlisten]) -> { state }

.listen takes the channel name, a function to handle each notify, and an optional function to run every time listen is registered and ready (happens on initial connect and reconnects). It returns a promise which resolves once the LISTEN query to Postgres completes, or if there is already a listener active.

await sql.listen('news', payload => {
  const json = JSON.parse(payload)
  console.log(json.this) // logs 'is'
})

The optional onlisten method is great to use for a very simply queue mechanism:

await sql.listen(
  'jobs',
  (x) => run(JSON.parse(x)),
  ( ) => sql`select unfinished_jobs()`.forEach(run)
)

function run(job) {
  // And here you do the work you please
}

Notify await sql.notify(channel, payload) -> Result[]

Notify can be done as usual in SQL, or by using the sql.notify method.

sql.notify('news', JSON.stringify({ no: 'this', is: 'news' }))

Realtime subscribe

Postgres.js implements the logical replication protocol of PostgreSQL to support subscription to real-time updates of insert, update and delete operations.

NOTE To make this work you must create the proper publications in your database, enable logical replication by setting wal_level = logical in postgresql.conf and connect using either a replication or superuser.

Quick start

Create a publication (eg. in migration)

CREATE PUBLICATION alltables FOR ALL TABLES

Subscribe to updates

const sql = postgres({ publications: 'alltables' })

const { unsubscribe } = await sql.subscribe(
  'insert:events',
  (row, { command, relation, key, old }) => {
    // Callback function for each row change
    // tell about new event row over eg. websockets or do something else
  },
  () => {
    // Callback on initial connect and potential reconnects
  }
)

Subscribe pattern

You can subscribe to specific operations, tables, or even rows with primary keys.

operation : schema . table = primary_key

operation is one of * | insert | update | delete and defaults to *

schema defaults to public

table is a specific table name and defaults to *

primary_key can be used to only subscribe to specific rows

Examples

sql.subscribe('*',                () => /* everything */ )
sql.subscribe('insert',           () => /* all inserts */ )
sql.subscribe('*:users',          () => /* all operations on the public.users table */ )
sql.subscribe('delete:users',     () => /* all deletes on the public.users table */ )
sql.subscribe('update:users=1',   () => /* all updates on the users row with a primary key = 1 */ )

Numbers, bigint, numeric

Number in javascript is only able to represent 2⁵³-1 safely which means that types in PostgreSQLs like bigint and numeric won't fit into Number.

Since Node.js v10.4 we can use BigInt to match the PostgreSQL type bigint which is returned for eg. count(*). Unfortunately, it doesn't work with JSON.stringify out of the box, so Postgres.js will return it as a string.

If you want to use BigInt you can add this custom type:

const sql = postgres({
  types: {
    bigint: postgres.BigInt
  }
})

There is currently no guaranteed way to handle numeric / decimal types in native Javascript. These [and similar] types will be returned as a string. The best way in this case is to use custom types.

Result Array

The Result Array returned from queries is a custom array allowing for easy destructuring or passing on directly to JSON.stringify or general Array usage. It includes the following properties.

.count

The count property is the number of affected rows returned by the database. This is useful for insert, update and delete operations to know the number of rows since .length will be 0 in these cases if not using RETURNING ....

.command

The command run by the query - eg. one of SELECT, UPDATE, INSERT, DELETE

.columns

The columns returned by the query useful to determine types, or map to the result values when using .values()

{
  name  : String,    // Column name,
  type  : oid,       // PostgreSQL oid column type
  parser: Function   // The function used by Postgres.js for parsing
}

.statement

The statement contains information about the statement implicitly created by Postgres.js.

{
  name    : String,  // The auto generated statement name
  string  : String,  // The actual query string executed
  types   : [oid],   // An array of oid expected as input parameters
  columns : [Column] // Array of columns - same as Result.columns
}

.state

This is the state { pid, secret } of the connection that executed the query.

Connection details

All Postgres options

const sql = postgres('postgres://username:password@host:port/database', {
  host                 : '',            // Postgres ip address[es] or domain name[s]
  port                 : 5432,          // Postgres server port[s]
  path                 : '',            // unix socket path (usually '/tmp')
  database             : '',            // Name of database to connect to
  username             : '',            // Username of database user
  password             : '',            // Password of database user
  ssl                  : false,         // true, prefer, require, tls.connect options
  max                  : 10,            // Max number of connections
  max_lifetime         : null,          // Max lifetime in seconds (more info below)
  idle_timeout         : 0,             // Idle connection timeout in seconds
  connect_timeout      : 30,            // Connect timeout in seconds
  prepare              : true,          // Automatic creation of prepared statements
  types                : [],            // Array of custom types, see more below
  onnotice             : fn,            // Default console.log, set false to silence NOTICE
  onparameter          : fn,            // (key, value) when server param change
  debug                : fn,            // Is called with (connection, query, params, types)
  socket               : fn,            // fn returning custom socket to use
  transform            : {
    undefined          : undefined,     // Transforms undefined values (eg. to null)
    column             : fn,            // Transforms incoming column names
    value              : fn,            // Transforms incoming row values
    row                : fn             // Transforms entire rows
  },
  connection           : {
    application_name   : 'postgres.js', // Default application_name
    ...                                 // Other connection parameters, see https://www.postgresql.org/docs/current/runtime-config-client.html
  },
  target_session_attrs : null,          // Use 'read-write' with multiple hosts to
                                        // ensure only connecting to primary
  fetch_types          : true,          // Automatically fetches types on connect
                                        // on initial connection.
})

Note that max_lifetime = 60 * (30 + Math.random() * 30) by default. This resolves to an interval between 30 and 60 minutes to optimize for the benefits of prepared statements and working nicely with Linux's OOM killer.

Dynamic passwords

When clients need to use alternative authentication schemes such as access tokens or connections to databases with rotating passwords, provide either a synchronous or asynchronous function that will resolve the dynamic password value at connection time.

const sql = postgres(url, {
  // Other connection config
  ...
  // Password function for the database user
  password : async () => await signer.getAuthToken(),
})

SSL

Although vulnerable to MITM attacks, a common configuration for the ssl option for some cloud providers is to set rejectUnauthorized to false (if NODE_ENV is production):

const sql =
  process.env.NODE_ENV === 'production'
    ? // "Unless you're using a Private or Shield Heroku Postgres database, Heroku Postgres does not currently support verifiable certificates"
      // https://help.heroku.com/3DELT3RK/why-can-t-my-third-party-utility-connect-to-heroku-postgres-with-ssl
      postgres({ ssl: { rejectUnauthorized: false } })
    : postgres()

For more information regarding ssl with postgres, check out the Node.js documentation for tls.

Multi-host connections - High Availability (HA)

Multiple connection strings can be passed to postgres() in the form of postgres('postgres://localhost:5432,localhost:5433', ...). This works the same as native the psql command. Read more at multiple host URIs.

Connections will be attempted in order of the specified hosts/ports. On a successful connection, all retries will be reset. This ensures that hosts can come up and down seamlessly.

If you specify target_session_attrs: 'primary' or PGTARGETSESSIONATTRS=primary Postgres.js will only connect to the primary host, allowing for zero downtime failovers.

The Connection Pool

Connections are created lazily once a query is created. This means that simply doing const sql = postgres(...) won't have any effect other than instantiating a new sql instance.

No connection will be made until a query is made.

For example:

const sql = postgres() // no connections are opened

await sql`...` // one connection is now opened
await sql`...` // previous opened connection is reused

// two connections are opened now
await Promise.all([
  sql`...`,
  sql`...`
])

When there are high amount of concurrent queries, postgres will open as many connections as needed up until max number of connections is reached. By default max is 10. This can be changed by setting max in the postgres() call. Example - postgres('connectionURL', { max: 20 }).

This means that we get a much simpler story for error handling and reconnections. Queries will be sent over the wire immediately on the next available connection in the pool. Connections are automatically taken out of the pool if you start a transaction using sql.begin(), and automatically returned to the pool once your transaction is done.

Any query which was already sent over the wire will be rejected if the connection is lost. It'll automatically defer to the error handling you have for that query, and since connections are lazy it'll automatically try to reconnect the next time a query is made. The benefit of this is no weird generic "onerror" handler that tries to get things back to normal, and also simpler application code since you don't have to handle errors out of context.

There are no guarantees about queries executing in order unless using a transaction with sql.begin() or setting max: 1. Of course doing a series of queries, one awaiting the other will work as expected, but that's just due to the nature of js async/promise handling, so it's not necessary for this library to be concerned with ordering.

Since this library automatically creates prepared statements, it also has a default max lifetime for connections to prevent memory bloat on the database itself. This is a random interval for each connection between 45 and 90 minutes. This allows multiple connections to independently come up and down without affecting the service.

Connection timeout

By default, connections will not close until .end() is called. However, it may be useful to have them close automatically when:

• re-instantiating multiple sql`` instances
• using Postgres.js in a Serverless environment (Lambda, etc.)
• using Postgres.js with a database service that automatically closes connections after some time (see ECONNRESET issue)

This can be done using the idle_timeout or max_lifetime options. These configuration options specify the number of seconds to wait before automatically closing an idle connection and the maximum time a connection can exist, respectively.

For example, to close a connection that has either been idle for 20 seconds or existed for more than 30 minutes:

const sql = postgres({
  idle_timeout: 20,
  max_lifetime: 60 * 30
})

Cloudflare Workers support

Postgres.js has built-in support for the TCP socket API in Cloudflare Workers, which is on-track to be standardized and adopted in Node.js and other JavaScript runtimes, such as Deno.

You can use Postgres.js directly in a Worker, or to benefit from connection pooling and query caching, via the Hyperdrive service available to Workers by passing the Hyperdrive connectionString when creating a new postgres client as follows:

// Requires Postgres.js 3.4.0 or later
import postgres from 'postgres'

interface Env {
    HYPERDRIVE: Hyperdrive;
}

export default async fetch(req: Request, env: Env, ctx: ExecutionContext) {
    // The Postgres.js library accepts a connection string directly
    const sql = postgres(env.HYPERDRIVE.connectionString)
    const results = await sql`SELECT * FROM users LIMIT 10`
    return Response.json(results)
}

In wrangler.toml you will need to enable the nodejs_compat compatibility flag to allow Postgres.js to operate in the Workers environment:

compatibility_flags = ["nodejs_compat"]

Auto fetching of array types

Postgres.js will automatically fetch table/array-type information when it first connects to a database.

If you have revoked access to pg_catalog this feature will no longer work and will need to be disabled.

You can disable this feature by setting fetch_types to false.

Environmental variables

It is also possible to connect to the database without a connection string or any options. Postgres.js will fall back to the common environment variables used by psql as in the table below:

const sql = postgres()

Option	Environment Variables
host	PGHOST
port	PGPORT
database	PGDATABASE
username	PGUSERNAME or PGUSER
password	PGPASSWORD
idle_timeout	PGIDLE_TIMEOUT
connect_timeout	PGCONNECT_TIMEOUT

Prepared statements

Prepared statements will automatically be created for any queries where it can be inferred that the query is static. This can be disabled by using the prepare: false option. For instance — this is useful when using PGBouncer in transaction mode.

Custom Types

You can add ergonomic support for custom types, or simply use sql.typed(value, type) inline, where type is the PostgreSQL oid for the type and the correctly serialized string. (oid values for types can be found in the pg_catalog.pg_type table.)

Adding Query helpers is the cleanest approach which can be done like this:

const sql = postgres({
  types: {
    rect: {
      // The pg_types oid to pass to the db along with the serialized value.
      to        : 1337,

      // An array of pg_types oids to handle when parsing values coming from the db.
      from      : [1337],

      //Function that transform values before sending them to the db.
      serialize : ({ x, y, width, height }) => [x, y, width, height],

      // Function that transforms values coming from the db.
      parse     : ([x, y, width, height]) => { x, y, width, height }
    }
  }
})

// Now you can use sql.typed.rect() as specified above
const [custom] = await sql`
  insert into rectangles (
    name,
    rect
  ) values (
    'wat',
    ${ sql.typed.rect({ x: 13, y: 37, width: 42, height: 80 }) }
  )
  returning *
`

// custom = { name: 'wat', rect: { x: 13, y: 37, width: 42, height: 80 } }

Custom socket

Easily do in-process ssh tunneling to your database by providing a custom socket for Postgres.js to use. The function (optionally async) must return a socket-like duplex stream.

Here's a sample using ssh2

import ssh2 from 'ssh2'

const sql = postgres({
  ...options,
  socket: ({ host: [host], port: [port] }) => new Promise((resolve, reject) => {
    const ssh = new ssh2.Client()
    ssh
    .on('error', reject)
    .on('ready', () =>
      ssh.forwardOut('127.0.0.1', 12345, host, port,
        (err, socket) => err ? reject(err) : resolve(socket)
      )
    )
    .connect(sshOptions)
  })
})

Teardown / Cleanup

To ensure proper teardown and cleanup on server restarts use await sql.end() before process.exit().

Calling sql.end() will reject new queries and return a Promise which resolves when all queries are finished and the underlying connections are closed. If a { timeout } option is provided any pending queries will be rejected once the timeout (in seconds) is reached and the connections will be destroyed.

Sample shutdown using Prexit

import prexit from 'prexit'

prexit(async () => {
  await sql.end({ timeout: 5 })
  await new Promise(r => server.close(r))
})

Reserving connections

await sql.reserve()

The reserve method pulls out a connection from the pool, and returns a client that wraps the single connection. This can be used for running queries on an isolated connection.

const reserved = await sql.reserve()
await reserved`select * from users`
await reserved.release()

reserved.release()

Once you have finished with the reserved connection, call release to add it back to the pool.

Error handling

Errors are all thrown to related queries and never globally. Errors coming from database itself are always in the native Postgres format, and the same goes for any Node.js errors eg. coming from the underlying connection.

Query errors will contain a stored error with the origin of the query to aid in tracing errors.

Query errors will also contain the query string and the parameters. These are not enumerable to avoid accidentally leaking confidential information in logs. To log these it is required to specifically access error.query and error.parameters, or set debug: true in options.

There are also the following errors specifically for this library.

UNSAFE_TRANSACTION

Only use sql.begin or max: 1

To ensure statements in a transaction runs on the same connection (which is required for them to run inside the transaction), you must use sql.begin(...) or only allow a single connection in options (max: 1).

UNDEFINED_VALUE

Undefined values are not allowed

Postgres.js won't accept undefined as values in tagged template queries since it becomes ambiguous what to do with the value. If you want to set something to null, use null explicitly.

MESSAGE_NOT_SUPPORTED

X (X) is not supported

Whenever a message is received from Postgres which is not supported by this library. Feel free to file an issue if you think something is missing.

MAX_PARAMETERS_EXCEEDED

Max number of parameters (65534) exceeded

The postgres protocol doesn't allow more than 65534 (16bit) parameters. If you run into this issue there are various workarounds such as using sql([...]) to escape values instead of passing them as parameters.

SASL_SIGNATURE_MISMATCH

Message type X not supported

When using SASL authentication the server responds with a signature at the end of the authentication flow which needs to match the one on the client. This is to avoid man-in-the-middle attacks. If you receive this error the connection was canceled because the server did not reply with the expected signature.

NOT_TAGGED_CALL

Query not called as a tagged template literal

Making queries has to be done using the sql function as a tagged template. This is to ensure parameters are serialized and passed to Postgres as query parameters with correct types and to avoid SQL injection.

AUTH_TYPE_NOT_IMPLEMENTED

Auth type X not implemented

Postgres supports many different authentication types. This one is not supported.

CONNECTION_CLOSED

write CONNECTION_CLOSED host:port

This error is thrown if the connection was closed without an error. This should not happen during normal operations, so please create an issue if this was unexpected.

CONNECTION_ENDED

write CONNECTION_ENDED host:port

This error is thrown if the user has called sql.end() and performed a query afterward.

CONNECTION_DESTROYED

write CONNECTION_DESTROYED host:port

This error is thrown for any queries that were pending when the timeout to sql.end({ timeout: X }) was reached.

CONNECTION_CONNECT_TIMEOUT

write CONNECTION_CONNECT_TIMEOUT host:port

This error is thrown if the startup phase of the connection (tcp, protocol negotiation, and auth) took more than the default 30 seconds or what was specified using connect_timeout or PGCONNECT_TIMEOUT.

TypeScript support

postgres has TypeScript support. You can pass a row list type for your queries in this way:

interface User {
  id: number
  name: string
}

const users = await sql<User[]>`SELECT * FROM users`
users[0].id // ok => number
users[1].name // ok => string
users[0].invalid // fails: `invalid` does not exists on `User`

However, be sure to check the array length to avoid accessing properties of undefined rows:

const users = await sql<User[]>`SELECT * FROM users WHERE id = ${id}`
if (!users.length)
  throw new Error('Not found')
return users[0]

You can also prefer destructuring when you only care about a fixed number of rows. In this case, we recommend you to prefer using tuples to handle undefined properly:

const [user]: [User?] = await sql`SELECT * FROM users WHERE id = ${id}`
if (!user) // => User | undefined
  throw new Error('Not found')
return user // => User

// NOTE:
const [first, second]: [User?] = await sql`SELECT * FROM users WHERE id = ${id}` // fails: `second` does not exist on `[User?]`
const [first, second] = await sql<[User?]>`SELECT * FROM users WHERE id = ${id}` // don't fail : `second: User | undefined`

We do our best to type all the public API, however types are not always updated when features are added or changed. Feel free to open an issue if you have trouble with types.

Migration tools

Postgres.js doesn't come with any migration solution since it's way out of scope, but here are some modules that support Postgres.js for migrations:

• https://github.com/porsager/postgres-shift
• https://github.com/lukeed/ley
• https://github.com/JAForbes/pgmg

Thank you

A really big thank you to @JAForbes who introduced me to Postgres and still holds my hand navigating all the great opportunities we have.

Thanks to @ACXgit for initial tests and dogfooding.

Also thanks to Ryan Dahl for letting me have the postgres npm package name.