I' wasn't sure about the SelectOpt
s only being applicable to entity value, so I checked that in a small snippet of code. Assuming an entity looks like this:
EntityA
key Text
time UTCTime
deriving Show
you can just list SelectOpt
s you're interested in and get the desirable output.
The sample code looks like this:
main :: IO ()
main = runSqlite ":memory:" $ do
runMigration migrateAll
currentTime <- liftIO getCurrentTime
-- insert some data
_ <- insert $ EntityA "first" currentTime
_ <- insert $ EntityA "second" currentTime
_ <- insert $ EntityA "third" currentTime
_ <- insert $ EntityA "fourth" currentTime
currentTime <- liftIO getCurrentTime
-- insert more data
_ <- insert $ EntityA "fifth" currentTime
_ <- insert $ EntityA "sixth" currentTime
_ <- insert $ EntityA "seventh" currentTime
_ <- insert $ EntityA "eighth" currentTime
currentTime <- liftIO getCurrentTime
-- insert more data
_ <- insert $ EntityA "this one will be first" currentTime
sorted <- selectList [] [Desc EntityATime, Asc EntityAId]
mapM_ (liftIO . print) sorted
and the output is:
Migrating: CREATE TABLE "entity_a"("id" INTEGER PRIMARY KEY,"key" VARCHAR NOT NULL,"time" TIMESTAMP NOT NULL)
Entity {entityKey = Key {unKey = PersistInt64 9}, entityVal = EntityA {entityAKey = "this one will be first", entityATime = 2014-05-07 20:15:35.627561 UTC}}
Entity {entityKey = Key {unKey = PersistInt64 5}, entityVal = EntityA {entityAKey = "fifth", entityATime = 2014-05-07 20:15:35.627026 UTC}}
Entity {entityKey = Key {unKey = PersistInt64 6}, entityVal = EntityA {entityAKey = "sixth", entityATime = 2014-05-07 20:15:35.627026 UTC}}
Entity {entityKey = Key {unKey = PersistInt64 7}, entityVal = EntityA {entityAKey = "seventh", entityATime = 2014-05-07 20:15:35.627026 UTC}}
Entity {entityKey = Key {unKey = PersistInt64 8}, entityVal = EntityA {entityAKey = "eighth", entityATime = 2014-05-07 20:15:35.627026 UTC}}
Entity {entityKey = Key {unKey = PersistInt64 1}, entityVal = EntityA {entityAKey = "first", entityATime = 2014-05-07 20:15:35.626622 UTC}}
Entity {entityKey = Key {unKey = PersistInt64 2}, entityVal = EntityA {entityAKey = "second", entityATime = 2014-05-07 20:15:35.626622 UTC}}
Entity {entityKey = Key {unKey = PersistInt64 3}, entityVal = EntityA {entityAKey = "third", entityATime = 2014-05-07 20:15:35.626622 UTC}}
Entity {entityKey = Key {unKey = PersistInt64 4}, entityVal = EntityA {entityAKey = "fourth", entityATime = 2014-05-07 20:15:35.626622 UTC}}
I can publish the sample project (it's on fpcomplete.com) if you're interested, but I guess this illustrates it well.