purescript-querydsl

A SQL query builder for Purescript, very loosely based on Java's Querydsl.

• Support standard SQL insert/update/delete/select queries.
• Allow building queries in a mostly type-safe and composable way.
• Generate reasonably readable SQL for monitoring and debugging.
• Support multiple underlying database platforms.

• Support create table syntax: these tend to be very database specific.

• Experimental, pre-alpha, full of bugs, lacking in features, unstable, don't rely on this, etc.
• Currently only SQLite is supported.

import Prelude
import Effect.Aff (Aff)
import QueryDsl (Column, Table, makeTable, from, select, where_, orderBy, limit, asc)
import QueryDsl.Expressions ((:==))
import QueryDsl.SQLite3 (runSelectManyQuery)
import SQLite3 (DBConnection)
import Type.Data.Boolean (False, True)

customer = makeTable "customer" :: Table (
  id :: Column Int False,
  firstName :: Column String True,
  lastName :: Column String True
)

getLastNames :: DBConnection -> Aff (Array { lastName :: String })
getLastNames db = do
  runSelectManyQuery db do
    c <- from customer
    pure $ select { lastName: c.lastName }
      `where_` (c.firstName :== "Bob")
      `orderBy` [asc c.id]
      `limit` 10

Querydsl requires that you call the makeTable function to create a value of type Table r for each table in your database. The row parameter r holds the types of the columns in the table, and must be given as a type assertion.

customer = makeTable "customer" :: Table (
  id :: Column Int False,
  firstName :: Column String True,
  lastName :: Column String True
)

The first parameter to each Column is the Purescript version of the database type, and the second parameter says whether this column is required for inserts or not. In this example id is not required because we know it is an auto-generated primary key column. Where columns are nullable in the database then it also might make sense for them to have required as False.

You can select rows from a table by creating a value of type SelectQuery and passing it to a database-specific run function (runSelectManyQuery in this case).

A monad is used to build the from-clause, and the value returned by the monad says what columns to select, and what where-clause/order-by/limit/etc to use.

runSelectManyQuery db do
  c <- from customer
  o <- innerJoin order (\o -> o.customer :== c.id)
  pure $ select {name: c.firstName, total: o.total} `where_` (o.total :>= 50)

For an insert you create an InsertQuery by calling insertInto with a record containing a value of the correct type for each non-optional column in the table, and possibly also values for the optional columns.

A database-specific run function is then used to execute the query (runQuery in this case).

runQuery db $ insertInto customer { firstName: "Jim", lastName: "Smith" }

To update a table you need a give update a record of expressions of the correct types for each column you want to update and a filtering expression that limits which rows are updated. If you want to update all rows then use alwaysTrue as the filter.

The columns function gives you access to expressions representing the columns of the table, if you need to refer to them in your update or filter expressions.

let c = columns customer in
runQuery db $ update customer { lastName: "Smythe" } (c.lastName :== "Smith")

To delete rows from a table you must provide deleteFrom with a filtering expression that selects the rows to delete.

let c = columns customer in
runQuery db $ deleteFrom customer (c.firstName :== "Paulo" :&& c.lastName :== "Coelho")

• With Bower: bower install purescript-querydsl --save.
• With Spago: Querydsl is not in a public package set, so you will have to add it to your packages.dhall. Refer to this project's spago.dhall to get the dependencies.
• You will also need yarn add sqlite3 to get the Node SQLite dependency.