@sequeljs/ast NPM

Sequel.js - AST

@sequeljs/ast is a SQL AST manager for JavaScript.

Installation

npm install --save @sequeljs/ast

A Gentle Introduction

Generating a query with Sequel.js AST is simple. For example, in order to produce

SELECT * FROM "users"

you construct a table relation and convert it to SQL:

let users = new Table('users')
users = users.project('*')
users.toSQL()

More Sophisticated Queries

Here is a whirlwind tour through the most common SQL operators. These will probably cover 80% of all interaction with the database.

First is the 'restriction' operator, where:

users.project('*').where(users.get('name').eq('amy'))
// SELECT * FROM "users" WHERE "users"."name" = 'amy'

What would, in SQL, be part of the SELECT clause is called in Sequel.js AST a projection:

users.project(users.get('id'))
// SELECT "users"."id" FROM "users"

Comparison operators =, !=, <, >, <=, >=, IN:

users.where(users.get('age').eq(10)).project('*')
// SELECT * FROM "users" WHERE "users"."age" = 10

users.where(users.get('age').notEq(10)).project('*')
// SELECT * FROM "users" WHERE "users"."age" != 10

users.where(users.get('age').lt(10)).project('*')
// SELECT * FROM "users" WHERE "users"."age" < 10

users.where(users.get('age').gt(10)).project('*')
// SELECT * FROM "users" WHERE "users"."age" > 10

users.where(users.get('age').lteq(10)).project('*')
// SELECT * FROM "users" WHERE "users"."age" <= 10

users.where(users.get('age').gteq(10)).project('*')
// SELECT * FROM "users" WHERE "users"."age" >= 10

users.where(users.get('age').inVal([20, 16, 17])).project('*')
// SELECT * FROM "users" WHERE "users"."age" IN (20, 16, 17)

Bitwise operators &, |, ^, <<, >>:

users.where((users.get('bitmap').bitwiseAnd(16)).gt(0)).project('*')
// SELECT * FROM "users" WHERE ("users"."bitmap" & 16) > 0

users.where((users.get('bitmap').bitwiseOr(16)).gt(0)).project('*')
// SELECT * FROM "users" WHERE ("users"."bitmap" | 16) > 0

users.where((users.get('bitmap').bitwiseXor(16)).gt(0)).project('*')
// SELECT * FROM "users" WHERE ("users"."bitmap" ^ 16) > 0

users.where((users.get('bitmap').bitwiseShiftLeft(1)).gt(0)).project('*')
// SELECT * FROM "users" WHERE ("users"."bitmap" << 1) > 0

users.where((users.get('bitmap').bitwiseShiftRight(1)).gt(0)).project('*')
// SELECT * FROM "users" WHERE ("users"."bitmap" >> 1) > 0

users.where((users.get('bitmap').bitwiseNot()).gt(0)).project('*')
// SELECT * FROM "users" WHERE  ~ "users"."bitmap" > 0

Joins resemble SQL strongly:

users.join(photos).on(users.get('id').eq(photos.get('user_id'))).project('*')
// SELECT * FROM "users" INNER JOIN "photos" ON "users"."id" = "photos"."user_id"

Left joins:

users.join(photos, OuterJoin).on(users.get('id').eq(photos.get('user_id'))).project('*')
// SELECT * FROM "users" LEFT OUTER JOIN "photos" ON "users"."id" = "photos"."user_id"

What are called LIMIT and OFFSET in SQL are called take and skip in Sequel.js AST:

users.take(5).project('*') // SSELECT * FROM "users" LIMIT 5
users.skip(4).project('*') // SELECT * FROM "users" OFFSET 4

GROUP BY is called group:

users.project(users.get('name')).group(users.get('name'))
// SELECT "users"."name" FROM "users" GROUP BY "users"."name"

The best property of Sequel.js AST is its "composability," or closure under all operations. For example, to restrict AND project, just "chain" the method invocations:

users
  .where(users.get('name').eq('amy'))
  .project(users.get('id'))
// SELECT "users"."id" FROM "users" WHERE "users"."name" = 'amy'

All operators are chainable in this way, and they are chainable any number of times, in any order.

users.where(users.get('name').eq('bob')).where(users.get('age').lt(25))

The OR operator works like this:

users.where(users.get('name').eq('bob').or(users.get('age').lt(25)))

The AND operator behaves similarly. Here is an example of the DISTINCT operator:

const posts = new Table('posts')
posts.project(posts.get('title')).distinct()
posts.toSQL() // SELECT DISTINCT "posts"."title" FROM "posts"

Aggregate functions AVG, SUM, COUNT, MIN, MAX, HAVING:

photos.group(photos.get('user_id')).having(photos.get('id').count().gt(5))
// SELECT FROM "photos" GROUP BY "photos"."user_id" HAVING COUNT("photos"."id") > 5

users.project(users.get('age').sum())
// SELECT SUM("users"."age") FROM "users"

users.project(users.get('age').average())
// SELECT AVG("users"."age") FROM "users"

users.project(users.get('age').maximum())
// SELECT MAX("users"."age") FROM "users"

users.project(users.get('age').minimum())
// SELECT MIN("users"."age") FROM "users"

users.project(users.get('age').count())
// SELECT COUNT("users"."age") FROM "users"

Aliasing Aggregate Functions:

users.project(users.get('age').average().as("mean_age"))
// SELECT AVG("users"."age") AS mean_age FROM "users"

The Advanced Features

The examples above are fairly simple and other libraries match or come close to matching the expressiveness of Sequel.js AST.

Inline math operations

Suppose we have a table products with prices in different currencies. And we have a table currency_rates, of constantly changing currency rates. In Sequel.js AST:

products = new Table('products')
// Attributes: ['id', 'name', 'price', 'currency_id']

currency_rates = new Table('currency_rates')
// Attributes: ['from_id', 'to_id', 'date', 'rate']

Now, to order products by price in user preferred currency simply call:

products
  .join('currency_rates')
  .on(products.get('currency_id').eq(currencyRates.get('from_id')))
  .where(currencyRates.get('to_id').eq(userPreferredCurrency))
  .where(currencyRates.get('date').eq(new Date()))
  .order(products.get('price').multiply(currencyRates.get('rate')))

Complex Joins

Alias

Where Sequel.js AST really shines is in its ability to handle complex joins and aggregations. As a first example, let's consider an "adjacency list", a tree represented in a table. Suppose we have a table comments, representing a threaded discussion:

comments = new Table('comments')

And this table has the following attributes:

// ['id', 'body', 'parent_id']

The parent_id column is a foreign key from the comments table to itself. Joining a table to itself requires aliasing in SQL. This aliasing can be handled from Sequel.js AST as below:

replies = comments.alias()
commentsWithReplies = comments
  .join(replies)
  .on(replies.get('parent_id').eq(comments.get('id')))
  .where(comments.get('id').eq(1))
  .project('*')

// SELECT * FROM "comments" INNER JOIN "comments" "comments_2"
// ON "comments_2"."parent_id" = "comments"."id"
// WHERE "comments"."id" = 1

This will return the reply for the first comment.

CTE

Common Table Expressions (CTE) support via:

Create a CTE

cteTable = new Table('cte_table')
composedCte = new Nodes.As(cteTable, photos.where(photos.get('created_at').gt(new Date('2021-01-01'))))

Use the created CTE:

users
  .join(cteTable)
  .on(users.get('id').eq(cteTable.get('user_id')))
  .project(users.get('id'), cteTable.get('click').sum())
  .with(composedCte)

// WITH "cte_table" AS (SELECT FROM "photos" WHERE "photos"."created_at" > '2021-01-01 00:00:00')
// SELECT "users"."id", SUM("cte_table"."click")
// FROM "users" INNER JOIN "cte_table" ON "users"."id" = "cte_table"."user_id"

Write SQL strings

When your query is too complex for Sequel.js AST, you can use Nodes.SQLLiteral:

photoClicks = new Nodes.SQLLiteral(`
  CASE WHEN condition1 THEN calculation1
  WHEN condition2 THEN calculation2
  WHEN condition3 THEN calculation3
  ELSE default_calculation END
  `)
photos.project(photoClicks.as("photo_clicks"))

// SELECT
// CASE WHEN condition1 THEN calculation1
// WHEN condition2 THEN calculation2
// WHEN condition3 THEN calculation3
// ELSE default_calculation END
//   AS photo_clicks FROM "photos"