@sequeljs/ast is a SQL AST manager for JavaScript.
npm install --save @sequeljs/astGenerating 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()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" > 0Joins 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 4GROUP 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 examples above are fairly simple and other libraries match or come close to matching the expressiveness of Sequel.js AST.
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')))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" = 1This will return the reply for the first comment.
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"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"Feel free to contribute with this library. For more information, take a look at our contributing guide.
@sequeljs/ast is basically a rewrite of
Rails' Arel
library in TypeScript.
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