Snippet for finding nearby locations using Postgres

Snippets.md

@@ -5,3 +5,7 @@ Generic useful pieces of code
 ## Dates
 
 * [Formatting dates](https://github.com/yesodweb/yesod-cookbook/blob/master/snippets/Formatting-dates.md)
+
+## Persistent
+
+* [Find nearby locations using Postgres](./snippets/Find-Nearby-Locations.md)

snippets/Find-Nearby-Locations.md

@@ -0,0 +1,88 @@
+# Find nearby locations using Postgres
+
+This snipped is the direct translation of the concept and code presented here in [google developer map resource](https://developers.google.com/maps/articles/phpsqlsearch_v3#findnearsql). The only difference here is that we are using `postgres` database instead of `mysql`.
+
+``` haskell
+#!/usr/bin/env stack
+{- stack
+     --resolver lts-6.11
+     --install-ghc
+     runghc
+     --package persistent
+     --package persistent-postgresql
+     --package persistent-template
+     --package mtl
+-}
+
+{-# LANGUAGE EmptyDataDecls             #-}
+{-# LANGUAGE FlexibleContexts           #-}
+{-# LANGUAGE GADTs                      #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE MultiParamTypeClasses      #-}
+{-# LANGUAGE OverloadedStrings          #-}
+{-# LANGUAGE QuasiQuotes                #-}
+{-# LANGUAGE TemplateHaskell            #-}
+{-# LANGUAGE TypeFamilies               #-}
+
+import Database.Persist
+import Database.Persist.Postgresql
+import Database.Persist.TH
+import Control.Monad.IO.Class  (liftIO)
+import Control.Monad.Logger    (runStderrLoggingT)
+import Control.Monad.Reader
+
+share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
+Markers
+    name String 
+    address String
+    lat Double
+    lon Double
+    deriving Show
+|]
+
+loadData :: MonadIO m => ReaderT SqlBackend m ()
+loadData = do
+  insert_ $ Markers "Frankie Johnnie & Luigo Too" "939 W El Camino Real, Mountain View, CA" 37.386339 (-122.085823)
+  insert_ $ Markers "Amici's East Coast Pizzeria" "790 Castro St  Mountain View  CA" 37.38714 (-122.083235)
+  insert_ $ Markers "Kapp's Pizza Bar & Grill" "191 Castro St  Mountain View  CA" 37.393885 (-122.078916)
+  insert_ $ Markers "Round Table Pizza: Mountain View" "570 N Shoreline Blvd  Mountain View  CA" 37.402653 (-122.079354)
+  insert_ $ Markers "Tony & Alba's Pizza & Pasta" "619 Escuela Ave  Mountain View  CA" 37.394011 (-122.095528)
+  insert_ $Markers "Oregano's Wood-Fired Pizza" "4546 El Camino Real  Los Altos  CA" 37.401724 (-122.114646)
+
+connStr = "host=localhost dbname=test1 user=postgres password=postgres port=5432"
+
+data GeoLocation = GeoLocation
+    { latitude :: Double,
+      longitude :: Double 
+    } deriving (Show, Eq, Ord)
+
+findNearbyMarkers :: (MonadIO m) => GeoLocation -> ReaderT SqlBackend m [(Single String, Single Double)]
+findNearbyMarkers (GeoLocation lat lon) = rawSql "SELECT name, ( 3959 * acos( cos( radians(37) ) * cos( radians( ? ) ) * cos( radians( ? ) - radians(-122) ) + sin( radians(37) ) * sin( radians( ? ) ) ) ) AS distance FROM markers" [PersistDouble lat, PersistDouble lon, PersistDouble lat]
+
+main :: IO ()
+main = runStderrLoggingT $ withPostgresqlPool connStr 10 $ liftSqlPersistMPool $ do
+         runMigration migrateAll
+         loadData
+         let geo = GeoLocation 37.0 (-122.0)
+         markers <- findNearbyMarkers geo
+         liftIO $ print "Nearby markers"
+         liftIO $ print markers
+```
+
+Execution:
+
+``` shellsession
+sibi::jane { ~/scripts }-> ./geo.hs
+Migrating: CREATe TABLE "markers"("id" SERIAL8  PRIMARY KEY UNIQUE,"name" VARCHAR NOT NULL,"address" VARCHAR NOT NULL,"lat" DOUBLE PRECISION NOT NULL,"lon" DOUBLE PRECISION NOT NULL)
+[Debug#SQL] CREATe TABLE "markers"("id" SERIAL8  PRIMARY KEY UNIQUE,"name" VARCHAR NOT NULL,"address" VARCHAR NOT NULL,"lat" DOUBLE PRECISION NOT NULL,"lon" DOUBLE PRECISION NOT NULL); []
+[Debug#SQL] INSERT INTO "markers"("name","address","lat","lon") VALUES(?,?,?,?) RETURNING "id"; [PersistText "Frankie Johnnie & Luigo Too",PersistText "939 W El Camino Real, Mountain View, CA",PersistDouble 37.386339,PersistDouble (-122.085823)]
+[Debug#SQL] INSERT INTO "markers"("name","address","lat","lon") VALUES(?,?,?,?) RETURNING "id"; [PersistText "Amici's East Coast Pizzeria",PersistText "790 Castro St  Mountain View  CA",PersistDouble 37.38714,PersistDouble (-122.083235)]
+[Debug#SQL] INSERT INTO "markers"("name","address","lat","lon") VALUES(?,?,?,?) RETURNING "id"; [PersistText "Kapp's Pizza Bar & Grill",PersistText "191 Castro St  Mountain View  CA",PersistDouble 37.393885,PersistDouble (-122.078916)]
+[Debug#SQL] INSERT INTO "markers"("name","address","lat","lon") VALUES(?,?,?,?) RETURNING "id"; [PersistText "Round Table Pizza: Mountain View",PersistText "570 N Shoreline Blvd  Mountain View  CA",PersistDouble 37.402653,PersistDouble (-122.079354)]
+[Debug#SQL] INSERT INTO "markers"("name","address","lat","lon") VALUES(?,?,?,?) RETURNING "id"; [PersistText "Tony & Alba's Pizza & Pasta",PersistText "619 Escuela Ave  Mountain View  CA",PersistDouble 37.394011,PersistDouble (-122.095528)]
+[Debug#SQL] INSERT INTO "markers"("name","address","lat","lon") VALUES(?,?,?,?) RETURNING "id"; [PersistText "Oregano's Wood-Fired Pizza",PersistText "4546 El Camino Real  Los Altos  CA",PersistDouble 37.401724,PersistDouble (-122.114646)]
+[Debug#SQL] SELECT name, ( 3959 * acos( cos( radians(37) ) * cos( radians( ? ) ) * cos( radians( ? ) - radians(-122) ) + sin( radians(37) ) * sin( radians( ? ) ) ) ) AS distance FROM markers; [PersistDouble 37.0,PersistDouble (-122.0),PersistDouble 37.0]
+"Nearby cities"
+[(Single {unSingle = "Frankie Johnnie & Luigo Too"},Single {unSingle = 0.0}),(Single {unSingle = "Amici's East Coast Pizzeria"},Single {unSingle = 0.0}),(Single {unSingle = "Kapp's Pizza Bar & Grill"},Single {unSingle = 0.0}),(Single {unSingle = "Round Table Pizza: Mountain View"},Single {unSingle = 0.0}),(Single {unSingle = "Tony & Alba's Pizza & Pasta"},Single {unSingle = 0.0}),(Single {unSingle = "Oregano's Wood-Fired Pizza"},Single {unSingle = 0.0})]
+```
+