-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Memory-constant streaming of Persistent entities from PostgreSQL
--   
--   This library provides a set of APIs for performing queries on
--   Persistent entities in constant memory, streaming the results using
--   <tt>conduit</tt>.
--   
--   The library relies on PostgreSQL-specific features to avoid loading
--   all the results of a query into memory at once. This allows for
--   accessing tables of millions of entities from Haskell without a memory
--   blow-up.
@package persistent-postgresql-streaming
@version 0.1.0.0

module Database.Persist.Postgresql.Streaming.Internal

-- | Run a <tt>Text</tt> query, with interpolated <tt>PersistValue</tt>s,
--   against a PostgreSQL backend using cursors, parsing the results with a
--   custom parser function and streaming them back.
--   
--   If the parser function returns <tt>Left</tt> for any row, a
--   <a>PersistException</a> will be thrown.
rawSelectStream :: MonadResource m => ([PersistValue] -> Either Text result) -> Text -> [PersistValue] -> ConduitT () result (ReaderT (RawPostgresql SqlBackend) m) ()

module Database.Persist.Postgresql.Streaming

-- | Run a query against a PostgreSQL backend, streaming back the results
--   in constant memory using the PostgreSQL cursor feature.
--   
--   NB: this function is likely to perform worse than <a>selectSource</a>
--   on small result sets.
--   
--   NB: for large result sets, this function is likely to perform very
--   poorly unless you manually configure the
--   <tt>cursor_tuple_fraction</tt> setting to be close to <tt>1</tt>. This
--   setting decides how much PostgreSQL will prioritise returning the
--   first rows quickly vs. returning all rows efficiently. See
--   
--   <a>https://postgresqlco.nf/doc/en/param/cursor_tuple_fraction/</a>
--   
--   for more.
selectStream :: (MonadResource m, MonadReader backend m, PersistRecordBackend record SqlBackend, BackendCompatible (RawPostgresql SqlBackend) backend) => [Filter record] -> [SelectOpt record] -> ConduitT () (Entity record) m ()