@sejohnson/tql v2.0.0

What is it?

pnpm i @sejohnson/tql

TQL (Template-SQL) is a lightweight library for writing SQL in TypeScript:

import { init, PostgresDialect } from '@sejohnson/tql';

const { query, fragment, IDENTIFIER, IDENTIFIERS, LIST, VALUES, SET, UNSAFE } = init({ dialect: PostgresDialect });

const [q, params] = query`SELECT * FROM users`;
// output: ['SELECT * FROM users', []]

Its API is simple -- everything starts and ends with query, which returns a tuple of the compiled query string and parameters to pass to your database. Some of the functions exported by this library are capitalized. The reason is twofold: First, they're meant to mirror some sort of SQL clause. We typically capitalize SQL clauses, so we capitalize their JavaScript equivalent. Second, this should help you remember that they're meant to be used inside this library's tagged template expressions. Oh, right, tagged template expressions. Let's talk about those!

A Primer on Tagged Templates

What is a tagged template in JavaScript? Quite simply, it's a function with the following signature:

function taggedTemplate(strings: TemplateStringsArray, ...values: unknown[]): any {
	// just like any regular function, you can return anything from here!
}

const parameterName = 'strings';
const result = taggedTemplate`The stringy parts of this are split on the "holes" and passed in as the "${variableName}" array!`;
// strings = ['The stringy parts of this are split on the "holes" and passed in as the ", " array!"]
// values: ['strings']

This is good news for SQL! The values in strings can only come directly from your code (as in, you as a developer definitely wrote them), which means they're always safe. We can then view the "holes" (anything between ${}) as a doorway through which more-exotic, potentially-unsafe things can be safely passed into your query.

But how do we know what to do with the special values passed through the "doorways"? Let's break it down. We need two pieces of semantic information:

• The developer's intent (what should the query compiler do with this information?)
• The actual data being passed through

This is trivially easy to do with classes -- if we only allow subclasses of a parent class (called TqlNode) to be passed in, then we can do something simple like this when building our query tree:

if (!value instanceof TqlNode) {
	return new TqlParameter(value);
}
return value;

Now we know all of the values we have are instances of our parent class, we can use which specific subclass they are to determine what to do with them. For example, if the node is a TqlParameter node, we would add a $1 (or whichever number it should have) into the query string and pass the node.data value into the parameters array.

API

To start, you'll need to initialize the query compiler:

import { init, PostgresDialect } from '@sejohnson/tql';

const { ... } = init({ dialect: PostgresDialect });

Missing your dialect? Feel free to open a PR -- they're pretty easy to write!

Below, you can see the utilities returned from init, but here's a summary table:

Important: Anywhere you pass a single value into query or fragment, you can also pass in an array of values. They'll be treated just as if you'd simply interpolated them right next to each other, with all the same protections.

Parameters

Anything directly passed into a template becomes a parameter. Essentially, the "holes" in the template are filled in with the dialect's parameter placeholder, and the value itself is passed directly into the parameters array:

const userId = 1234;
const [q, params] = query`SELECT * FROM users WHERE user_id = ${userId}`;
// output: ['SELECT * FROM users WHERE user_id = $1', [1234]]

List parameters

Need to use list syntax?:

const userId = [1234, 5678];
const [q, params] = query`SELECT * FROM users WHERE user_id IN ${LIST(userId)}`;
// output: ['SELECT * FROM users WHERE user_id IN ($1, $2)', [1234, 5678]]

Composable queries

Need to share clauses between queries, or do you just find it more convenient to build a specific query in multiple variable declarations? fragment is what you're looking for!

const userId = 1234;
const whereClause = fragment`WHERE user_id = ${userId}`;
const [q, params] = query`SELECT * FROM users ${whereClause}`;
// output: ['SELECT * FROM users WHERE user_id = $1', [1234]]

Fragments can be nested recursively, so the possibilities are endless.

If you need to combine a group of fragments, you can use fragment.join, which accepts a delimiter and an array of things to join:

const maxAge = 30;
const minAge = 25;
const firstName = undefined;

const filters = [];
if (maxAge) filters.push(fragment`age < ${maxAge}`);
if (minAge) filters.push(fragment`age > ${minAge}`);
if (firstName) filters.push(fragment`firstName = ${firstName}`);

let whereClause = fragment``;
if (filters.length > 0) {
	// note that the delimiter is a fragment -- if you were to pass just the string
	// ` AND `, `query` would end up substituting parameters in place of it, as "naked" strings
	// are untrustworthy.
	joinedFilters = fragment.join(fragment` AND `, filters);
	whereClause = fragment`WHERE ${joinedFilters}`;
}
const [q, params] = query`SELECT * FROM users ${whereClause};`;
// output: [
//   'SELECT * FROM users WHERE age < $1 AND age > $2;',
//   [30, 25]
// ]

If you need to arbitrarily combine templates, don't forget that they're nestable:

const select = fragment`SELECT *`;
const from = fragment`FROM users`;
const where = fragment`WHERE user_id = ${1234}`;
// somehow, the paramters will all be interpolated in the right order, no matter what!
const cte = fragment`${select} ${from} ${where}`;
const [q, params] = query`
WITH user AS (${cte})
SELECT * FROM user;
`;
// output: [
//   `WITH user AS (SELECT * FROM users WHERE user_id = $1)
//    SELECT * FROM user`,
//   [1234]
// ]

Identifiers

Need to dynamically insert identifiers?

const columns = ['name', 'dob'];
const [q, params] = query`SELECT ${IDENTIFIERS(columns)} FROM users`;
// output: ['SELECT "name", "dob" FROM users', []]

Note: Dotted identifiers are escaped with all sides quoted, so dbo.users would become "dbo"."users".

VALUES clauses

Inserting records is a pain!

const users = [
	{ name: 'vercelliott', favorite_hobby: 'screaming into the void' },
	{ name: 'reselliott', favorite_hobby: 'thrifting' },
];
const [q, params] = query`INSERT INTO users ${VALUES(users)}`;
// output: [
//   'INSERT INTO users ("name", "favorite_hobby") VALUES ($1, $2), ($3, $4)',
//   ['vercelliott', 'screaming into the void', 'reselliott', 'thrifting']
//  ]

VALUES also accepts just one record instead of an array. If an array is passed, it will validate that all records have the same columns.

SET clauses

Updating records can also be a pain!

const updatedUser = { name: 'vercelliott' };
const userId = 1234;
const [q, params] = query`UPDATE users ${SET(updatedUser)} WHERE userId = ${userId}`;
// output: ['UPDATE users SET "name" = $1 WHERE userId = $2', ['vercelliott', 1234]]

UNSAFE

This is just a tagged template that will be verbatim-inserted into your query. It is unsafe, do not pass unsanitized user input into it!

I want to...

As people ask questions about how to do various things, I'll fill out this section as a sort of FAQ.