31 Mar 2022, 20:00

PureScript web app for dummies - part 3



In the previous post, we created a little client side app to create, update and delete notes

It works well, but it is not very useful because nothing is being persisted

Now we are going to add a database to the server

PureScript web app for dummies series

02 Mar 2022set up a basic HTTPure serverhttps://tiago.dalligna.com/2022/03/purescript-web-app-for-dummies-part-1/
07 Mar 2022add a client side apphttps://tiago.dalligna.com/2022/03/purescript-web-app-for-dummies-part-2/
31 Mar 2022add a database, API, and unit testshttps://tiago.dalligna.com/2022/03/purescript-web-app-for-dummies-part-3/
11 Apr 2022connect frontend client to the apihttps://tiago.dalligna.com/2022/04/purescript-web-app-for-dummies-part-4/

Prepare your project to sqlite

step 1: add sqlite to spago AND npm

spago install sqlite3
npm install sqlite3

step 2: add *.db to your gitignore (you dont want to save your database in git).

Add a database access file

I will not paste the whole file here, but only the most important bits instead.

We start with some helper functions.

module Server.Database where
-- This type is just a to add the Aff monad
type InitDBType a = forall m. MonadAff m => m a

-- So now we return our InitDBType together with the connection because of the Aff
openDb :: String -> InitDBType Sqlite.DBConnection
openDb filename = liftAff $ Sqlite.newDB filename

-- just a helper to make queries (return values)
query ::  a. ReadForeign a => String -> Array String -> Aff (Array a)
query sql params = do
  db <- init
  liftAff (Sqlite.queryDB db sql (unsafeToForeign <$> params))
    <#> read
    >>> hush
    >>> fromMaybe []
-- same as query, but it ignores the response
run :: String -> Array String -> InitDBType Unit
run sql params = do
  db <- init
  liftAff $ void $ Sqlite.queryDB db sql (unsafeToForeign <$> params)

-- this is a poor man's migration runner
init :: InitDBType Sqlite.DBConnection
init = do
  let dbFilename = "notes.db"
  (liftAff $ FS.exists dbFilename) >>= case _ of
    false -> createDb dbFilename *> openDb dbFilename
    true -> openDb dbFilename
-- and here the poor man's migrations
createDb :: String -> InitDBType Unit
createDb filename = do
  db <- liftAff $ Sqlite.newDB filename
  liftAff $ Sqlite.closeDB db
  run "CREATE TABLE IF NOT EXISTS notes( title text, content text, createdAt text PRIMARY KEY);" []

This comments are not saved in the github. Should I put it there? It feels a bit too much…

anyway, this is how to use it:

-- the query result will be automatically parsed to the return type (Array Note)
getNotes :: String -> Aff (Array Note)
getNotes str =
  query "SELECT * FROM notes" [ ]

-- to run a command is similar, but the return type is just Unit
saveNote :: Note -> Aff Unit
saveNote note = 
      INSERT INTO notes (title, content, createdAt) VALUES (@title, @content, @createdAt)
      ON CONFLICT(createdAt) DO UPDATE SET title=@title, content=@content WHERE createdAt=@createdAt
    [ note.title, note.content, note.createdAt ]

Create an api file, nothing special, just parse the parameters and call the db, such as:

saveNote :: String -> String -> HTTPure.ResponseM
saveNote token body = case JSON.readJSON body of
  Right (note :: Note) -> do
    notes <- DB.saveNote note
    HTTPure.ok "ok"
  Left err -> HTTPure.internalServerError (show err)

Now we have to modify our Router to include this new Api endpoints

router { body, query, headers, method, path } = do

  bodyString <- HTTPure.toString body

  case method, path of
    HTTPure.Get, [ "api", "notes" ] -> API.getNotes "token"
    HTTPure.Post, [ "api", "note" ] -> API.saveNote "token" bodyString
    HTTPure.Delete, [ "api", "note", id ] -> API.deleteNote "token" id

Pretty straightforward, just call the api

Except, while creating this, the new version of HTTPure is out, and body is not a string anymore.

So that is why we had to create the bodyString value

This is not too bad right? but how do we test it?

well, we start with a simple Request using VS Code rest client:

POST http://localhost:8080/api/note

{ "title": "the test note"
, "content": "bla bla bla"
, "createdAt": "2022-03-19T10:20:30"

GET http://localhost:8080/api/notes

DELETE http://localhost:8080/api/note/2022-03-19 

cool right?

well, not really… it works but by now we should start thinking about something that has been so neglected so far

Unit testing

Unit testing in purs is quite simple. You add a lib, describe is just to group the similar tests.

For each test include an it section describing the test.

main :: Effect Unit
main = launchAff_ $ runSpec [console reporter] do
describe "DB" do
it "insert" do 
let note = { title: "the test note", content: "bla bla bla", createdAt: "2022-03-19T10:20:30"} 
DB.saveNote note 
dbNotes <- DB.getNotes "" 
dbNotes `shouldContain` note

I will just leave this test code here and link to the github

It is pretty self explanatory

PS: a function surrounded by backticks can be place in between 2 parameters for improved readability. ex:

dbNotes `shouldContain` note
-- is the same as
shouldContain dbNotes note


This post thought you how to add an sqlite database to your app, adapt the api to serve it, and create unit tests.

The code is available in the tag v5 of our pnotes repo.

So far, so good.

But… why is my app is still not saving/loading/deleting in/from the database? Well, our client side is not calling our API yet. But this will be fixed in the next post.