s9gf4ult/hdbi

Haskell Database Connectivity

HDBI

Welcome to HDBI, Haskell Database Independent interface.

HDBI is the fork of HDBC. This is just improved HDBC with new features.

Installation

Tested on GHC-7.4 but must work on older and newer versions, HUGS is not supported for now.

The steps to install are:

cabal install hdbi

hdbi's Issues

Make the statements tagged

Make the statements tagged

prepare :: Connection -> Query -> Tagged New Statement
execute :: Tagged New Statement -> Tagged Executed Statement
finish :: Tagged a Statement -> Tagged Finished Statement
reset :: Tagged a Statement -> Tagged New Statement

This brings the lifecycle of the statements to typelevel.

Add support of nested transactions

Many databases support nested transactions through "savepoints". We could add this feature to withTransaction function, but this one must be a method of Connection because savepoints are implemented differently in databases. There is also some another differences in databases, so this is more logical to do withTransaction as Connection method and remove begin rollback and commit methods to unleash a driver developer's hands.

remove `affectedRows` from `Statement`

SQlite does not support this feature on statement level so it must be moved from common interface to database-specific

withTransaction and similar combinators must use MonadIO

withTransaction has type

withTransaction :: Connection conn => conn -> IO a -> IO a

which means we can just IO as inner action, this must be MonadIO instead.

The same is for other such combinators.

Make named parameters posible

Add named request parameter placeholders like select * from tbl where fld1 = :param1: and fld2 in :param1: to :param2:

We will need also some method like

executeNamed :: Statement -> [(ParamName, SqlValue)] -> IO ()

to execute such a queries. This will also need a special query parser

Documentation for difference between hdbi and hdbc

It would be great if there was documentation for how hdbi differs from hdbc.

`FromRow` and `ToRow` typeclasses

Add typeclasses FromRow and ToRow to simplify data convertion between database and Haskell.

class FromRow a where
  fromRow :: [SqlValue] -> a

class ToRow a where
  toRow :: a -> [SqlValue]

Note, that typeclass Statement should not change, this is logical to add separate functions for statement execution and row fetching like this

executeRow :: (Statement stmt, ToRow r) => stmt -> r -> IO ()
fetchFromRow :: (Statement stmt, FromRow r) => stmt -> IO (Maybe r)