Btukfyl

I would like to run PureScript code in AWS Lambda. Normally, if a lambda function has to call the database, the connection is stored in a global variable. Excuse me if the following JavaScript code is syntactically wrong as I don't write JavaScript but something like below is what I want(this is the code expected by AWS Lambda):

function createConnection() {

    connection = SomeDBLibrary.createConnection(username, pwd)

    return connection;

}

global.db_connection = createConnection();



handler = (event, context, callback) => {

    // TODO use global.db_connection here to call the database

};



module.exports {

 handler: handler

};

How do I write the equivalent PureScript to get such code? Currently, I call the createConnection() function in each of my CRUD methods which is wasteful.

Edit 1:

My actual PureScript code is below. The function which I want to call only once is aPool. However, I believe it's being called everytime one hits the /list endpoint. I would like it to be hit only once when the handler is loaded for the first time.

module Main where



import Prelude hiding (apply)



import Data.Bifunctor (lmap)

import Data.Either (Either)

import Database.Postgres (Client, ClientConfig, ConnectionInfo, Pool, Query(Query), connectionInfoFromConfig, defaultPoolConfig, mkPool, query_, withClient)

import Effect (Effect)

import Effect.Aff (Aff)

import Effect.Aff.Class (liftAff)

import Effect.Class (class MonadEffect, liftEffect)

import Effect.Console (log)

import Effect.Exception (Error, error)

import Foreign (Foreign)

import Node.Express.App (App, get)

import Node.Express.Handler (Handler)

import Node.Express.Response (sendJson)

import Simple.JSON as JSON

import Network.AWS.Lambda.Express as Lambda





clientConfig :: ClientConfig

clientConfig =

  { host: "localhost"

  , database: "test"

  , port: 5432

  , user: "testuser"

  , password: "test"

  , ssl: false

  }



type IndexedTodo = { id :: Int, description :: String, isdone :: Boolean }



connectionInfo :: ConnectionInfo

connectionInfo = connectionInfoFromConfig clientConfig defaultPoolConfig



println :: forall a. MonadEffect a => String -> a Unit

println str =  liftEffect $ log str



aPool :: Effect Pool

aPool = do

  println "In Pooler"

  mkPool connectionInfo



withConnectionPool :: forall a. Effect Pool -> (Client -> Aff a) -> Aff a

withConnectionPool somePool f = do

  pool <- liftEffect somePool

  withClient pool c -> f c



withConnection :: forall a. (Client -> Aff a) -> Aff a

withConnection = withConnectionPool aPool



read' :: forall a. JSON.ReadForeign a => Foreign -> Either Error a

read' = lmap (error <<< show) <<< JSON.read



readTodoList :: Aff (Array IndexedTodo)

readTodoList = do

  let selectQuery = Query "select * from todos" :: Query IndexedTodo

  withConnection $ query_ read' selectQuery



listTodosHandler :: Handler

listTodosHandler = do

  userdata <- liftAff readTodoList

  sendJson userdata





app :: App

app = do

  get "/list"       listTodosHandler



-- Define the AWS Lambda handler

handler :: Lambda.HttpHandler

handler = Lambda.makeHandler app

I think that this requires a FFI like:

foreign import dbConnection :: Effect Connection

with implementation:

exports.dbConnection = function() {

  if(globals.dbConnection === undefined) {

    globals.dbConnection = createConnection();

  }

  return globals.dbConnection;

}