4e9e90d · rel8 · git.iko.soy

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Expand on `select` needing a connection

4e9e90dOllie Charles5 years ago

docs/tutorial.rst+16−13

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unifiedsplit

@@ -204,10 +204,13 @@ Recall we defined ``projectAuthorId`` as ``Column f AuthorId``. Now we have

204We'll see more about ``Expr`` soon, but you can think of ``Expr a`` as "SQL

205expressions of type ``a``\".

206

207−To execute this ``Query``, we pass it to ``select``::

207+To execute this ``Query``, we pass it to ``select``. This function takes both a

208+database connection (which can be obtained using hasql's ``acquire`` function),

209+and the ``Query`` to run::

208

210

211+ >>> Right conn <- acquire "user=postgres"

209− >>> :t select c (each projectSchema)

212+ >>> :t select conn (each projectSchema)

210− select c (each projectSchema) :: MonadIO m => m [Project Result]

213+ select conn (each projectSchema) :: MonadIO m => m [Project Result]

211

214

212When we ``select`` things containing ``Expr``\s, Rel8 builds a new response

215When we ``select`` things containing ``Expr``\s, Rel8 builds a new response

213table with the ``Result`` interpretation. This means you'll get back plain

216table with the ``Result`` interpretation. This means you'll get back plain

@@ -222,7 +225,7 @@ wrappping type at all.

222

225

223Putting this all together, we can run our first query::

226Putting this all together, we can run our first query::

224

227

225− >>> select c (each projectSchema) >>= mapM_ print

228+ >>> select conn (each projectSchema) >>= mapM_ print

226 Project {projectAuthorId = 1, projectName = "rel8"}

229 Project {projectAuthorId = 1, projectName = "rel8"}

227 Project {projectAuthorId = 2, projectName = "aeson"}

230 Project {projectAuthorId = 2, projectName = "aeson"}

228 Project {projectAuthorId = 2, projectName = "text"}

231 Project {projectAuthorId = 2, projectName = "text"}

@@ -232,7 +235,7 @@ sometimes we're only interested in a subset of the columns of a table. To

232restrict the returned columns, we can specify a projection by using ``Query``\s

235restrict the returned columns, we can specify a projection by using ``Query``\s

233``Functor`` instance::

236``Functor`` instance::

234

237

235− >>> select c $ projectName <$> each projectSchema

238+ >>> select conn $ projectName <$> each projectSchema

236 ["rel8","aeson","text"]

239 ["rel8","aeson","text"]

237

240

238Joins

241Joins

@@ -248,7 +251,7 @@ We can do this by simply calling ``each`` twice, and then returning a tuple of

248their results::

251their results::

249

252

250 >>> :{

253 >>> :{

251− mapM_ print =<< select c do

254+ mapM_ print =<< select conn do

252 author <- each authorSchema

255 author <- each authorSchema

253 project <- each projectSchema

256 project <- each projectSchema

254 return (projectName project, authorName author)

257 return (projectName project, authorName author)

@@ -267,7 +270,7 @@ This isn't quite right, though, as we have ended up pairing up the wrong

267projects and authors. To fix this, we can use ``where_`` to restrict the

270projects and authors. To fix this, we can use ``where_`` to restrict the

268returned rows. We could write::

271returned rows. We could write::

269

272

270− select c $ do

273+ select conn $ do

271 author <- each authorSchema

274 author <- each authorSchema

272 project <- each projectSchema

275 project <- each projectSchema

273 where_ $ projectAuthorId project ==. authorId author

276 where_ $ projectAuthorId project ==. authorId author

@@ -284,7 +287,7 @@ for the particular joins in your database. In our case, this would be::

284Our final query is then::

287Our final query is then::

285

288

286 >>> :{

289 >>> :{

287− mapM_ print =<< select c do

290+ mapM_ print =<< select conn do

288 author <- each authorSchema

291 author <- each authorSchema

289 project <- projectsForAuthor author

292 project <- projectsForAuthor author

290 return (projectName project, authorName author)

293 return (projectName project, authorName author)

@@ -303,7 +306,7 @@ transformer to allow for the possibility of the join to fail.

303In our test database, we can see that there's another author who we haven't

306In our test database, we can see that there's another author who we haven't

304seen yet::

307seen yet::

305

308

306− >>> select c $ authorName <$> each authorSchema

309+ >>> select conn $ authorName <$> each authorSchema

307 ["Ollie","Bryan O'Sullivan","Emily Pillmore"]

310 ["Ollie","Bryan O'Sullivan","Emily Pillmore"]

308

311

309Emily wasn't returned in our earlier query because - in our database - she

312Emily wasn't returned in our earlier query because - in our database - she

@@ -311,7 +314,7 @@ doesn't have any registered projects. We can account for this partiality in our

311original query by wrapping the ``projectsForAuthor`` call with ``optional``::

314original query by wrapping the ``projectsForAuthor`` call with ``optional``::

312

315

313 >>> :{

316 >>> :{

314− mapM_ print =<< select c do

317+ mapM_ print =<< select conn do

315 author <- each authorSchema

318 author <- each authorSchema

316 mproject <- optional $ projectsForAuthor author

319 mproject <- optional $ projectsForAuthor author

317 return (authorName author, projectName <$> mproject)

320 return (authorName author, projectName <$> mproject)

@@ -356,8 +359,8 @@ focus on the /type/ of that query::

356 return (author, project)

359 return (author, project)

357 where

360 where

358

361

359− >>> :t select c authorsAndProjects

362+ >>> :t select conn authorsAndProjects

360− select c authorsAndProjects

363+ select conn authorsAndProjects

361 :: MonadIO m => m [(Author Result, Project Result)]

364 :: MonadIO m => m [(Author Result, Project Result)]

362

365

363

366

@@ -374,7 +377,7 @@ simply wrapping the call to ``projectsForAuthor`` with either ``some`` or

374author to have no projects::

377author to have no projects::

375

378

376 >>> :{

379 >>> :{

377− mapM_ print =<< select c do

380+ mapM_ print =<< select conn do

378 author <- each authorSchema

381 author <- each authorSchema

379 projectNames <- many $ projectName <$> projectsForAuthor author

382 projectNames <- many $ projectName <$> projectsForAuthor author

380 return (authorName author, projectNames)

383 return (authorName author, projectNames)