Database.TemplatePG.SQL

This module exposes the high-level Template Haskell interface for querying and manipulating the PostgreSQL server.

All SQL string arguments support expression interpolation. Just enclose your expression in {} in the SQL string.

Note that transactions are messy and untested. Attempt to use them at your own risk.

Documentation

queryTuples :: String -> Q Exp

queryTuples :: String -> (Handle -> IO [(column1, column2, ...)])

Query a PostgreSQL server and return the results as a list of tuples.

Example (where h is a handle from pgConnect):

@$(queryTuples "SELECT usesysid, usename FROM pg_user") h

> IO [(Maybe String, Maybe Integer)]

@

queryTuple :: String -> Q Exp

queryTuple :: String -> (Handle -> IO (Maybe (column1, column2, ...)))

Convenience function to query a PostgreSQL server and return the first result as a tuple. If the query produces no results, return Nothing.

Example (where h is a handle from pgConnect):

@let sysid = 10::Integer;

$(queryTuple "SELECT usesysid, usename FROM pg_user WHERE usesysid = {sysid}") h

> IO (Maybe (Maybe String, Maybe Integer))

@

execute :: String -> Q Exp

execute :: String -> (Handle -> IO ())

Convenience function to execute a statement on the PostgreSQL server.

Example (where h is a handle from pgConnect):

@let rolename = "BOfH"

$(execute "CREATE ROLE {rolename}") h @

insertIgnore :: IO () -> IO ()

Ignore duplicate key errors. This is also limited to the IO Monad.

withTransaction :: Handle -> IO a -> IO a

Run a sequence of IO actions (presumably SQL statements) wrapped in a transaction. Unfortunately you're restricted to using this in the IO Monad for now due to the use of onException. I'm debating adding a MonadPeelIO version.

rollback :: Handle -> IO ()

Roll back a transaction.

thConnection :: IO Handle

Grab a PostgreSQL connection for compile time. We do so through the environment variables: TPG_DB, TPG_HOST, TPG_PORT, TPG_USER, and TPG_PASS. Only TPG_DB is required.