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Applications and libraries/Database interfaces/HaskellDB

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== Introduction ==
 
== Introduction ==
   
A [[combinator]] library for declarative, type safe database management. A domain specific embedded language, containing the concept of [[extensible record]] and a special Query [[monad]] (among other powerful ideas, see [[#Related concepts]]).
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A [[combinator]] library for declarative, type safe database management. All queries and operations can be expressed in Haskell. No SQL need be written!
   
All the queries and operations are completely expressed within Haskell, no embedded (SQL) commands are needed.
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[http://hackage.haskell.org/package/haskelldb Hackage] hosts the [http://hackage.haskell.org/package/haskelldb latest release of HaskellDB]. The project home page can be found at http://trac.haskell.org/haskelldb.
   
== Status ==
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==== Archived Information ====
   
HaskellDB, pulled from it's repository, builds on GHC 6.10.1.
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Archive information from this page can be found on [[Applications and libraries/Database interfaces/HaskellDB/Archive]].
 
Some of HaskellDB HDBC backends (ODBC and SQLite3 to be exact) have been updated to work with recent HDBC (2.1 as of this writing).
 
 
This library is in need of some tender love and care. Drop a mail at HaskellDB mailing list if you're interested in improving code or documentation.
 
 
== Homes ==
 
 
=== Current Version ===
 
The current repository is stored at code.haskell.org.
 
There was a [http://www.haskell.org/pipermail/haskell-cafe/2008-December/051557.html complaint on Haskell-cafe] that HaskellDB does not compile with GHC 6.10.1. This is only partially true: one can darcs get HaskellDB repository and build it themselves.
 
 
The following procedure worked as of October, 2008:
 
* GHC 6.8.3
 
* Cabal 1.6(?)
 
* HDBC 1.1.5
 
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC
 
runghc Setup.lhs configure
 
runghc Setup.lhs build
 
sudo runghc Setup.lhs install
 
* HDBC.ODBC 1.1.4.4
 
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC-odbc
 
runghc Setup.hs configure
 
runghc Setup.hs build
 
sudo runghc Setup.hs install
 
* HaskellDB - patch 743
 
darcs get http://code.haskell.org/haskelldb
 
runghc Setup.hs configure
 
runghc Setup.hs build
 
sudo runghc Setup.hs install
 
cd driver-hdbc
 
runghc Setup.hs configure
 
runghc Setup.hs build
 
sudo runghc Setup.hs install
 
cd ../driver-hdbc-odbc
 
runghc Setup.hs configure
 
runghc Setup.hs build
 
sudo runghc Setup.hs install
 
 
=== [http://www.haskell.org/haskellDB/index.html Daan Leijen's original version] ===
 
It makes possible to use Haskell's typecheck system for a type-safe, declarative database management -- a combinator library. It can prevent the user even from using multiple labels in the same record, but the price for this: it needs a special extension of Haskell called Trex (providing [[extensible record]]s).
 
 
HaskellDB was originally developed by Daan Leijen, and is described in the paper Domain Specific Embedded Compilers, Daan Leijen and Erik Meijer. 2nd USENIX Conference on Domain-Specific Languages (DSL), Austin, USA, October 1999.
 
 
=== [http://haskelldb.sourceforge.net Chalmers version] ===
 
A student project by Björn Bringert, Anders Höckersten, Conny Andersson, Martin Andersson, Mary Bergman, Victor Blomqvist, Torbjörn Martin.
 
 
It works well with the most common Haskell implementations, because [[extensible record]]s (without check for multiple labels) are implemented in a way which does not need the Trex extension of Haskell.
 
 
See also Björn Bringert's slides [http://www.cs.chalmers.se/~bringert/publ/haskelldb/haskelldb-db-2005.pdf HaskellDB -- Type safe declarative database combinators].
 
 
== Other materials ==
 
 
=== How to use ===
 
 
HaskellDB needs database schema expressed in Haskell to operate (not only a schema, but also some boilerplate, too: fortunately, it can be derived automagically). Furthermore, HaskellDB description and real database schema should be kept in sync.
 
 
Here's an example of creating both database tables and appropriate Haskell boilerplate out of database specification.
 
 
<haskell>
 
-- Compile with:
 
-- ghc --make <filename>
 
---------------------------------
 
-- Compile a Haskell description of a database (from a DBInfo)
 
--
 
import Database.HaskellDB
 
import Database.HaskellDB.DBSpec.DBSpecToDBDirect
 
import Database.HaskellDB.DBSpec
 
import Database.HaskellDB.HDBC.ODBC
 
import Database.HaskellDB.DBSpec.PPHelpers
 
 
---------------------------------
 
-- Connect to a DSN through ODBC
 
withDB dsn = (connect driver) [ ("dsn",dsn) ]
 
 
---------------------------------
 
-- An example Database
 
testdb = DBInfo {dbname = "test", opts = testopts, tbls = [testtbl1]}
 
testopts = DBOptions {useBString = False, makeIdent = mkIdentPreserving}
 
testtbl1 = TInfo {tname = "test_tbl", cols = [testcol11,testcol12]}
 
testcol11 = CInfo {cname = "c11", descr = (IntT,False)}
 
testcol12 = CInfo {cname = "c12", descr = (IntT,True)}
 
 
---------------------------------
 
main = do
 
-- Generate the database type import files from the DBInfo structure
 
dbInfoToModuleFiles "" "Test" testdb
 
 
-- Create the database tables
 
withDB "testdsn" $ \db -> dbSpecToDatabase db testdb
 
</haskell>
 
 
Now we can express queries in a nice declarative and type-safe manner:
 
 
<haskell>
 
-- Compile with:
 
-- ghc --make <filename>
 
----------------------------------------------
 
-- Query the database and print results
 
--
 
import Database.HaskellDB
 
import Database.HaskellDB.DBSpec.DBSpecToDBDirect
 
import Database.HaskellDB.DBSpec
 
import Database.HaskellDB.HDBC.ODBC
 
 
-- This file generated from "dbInfoToModuleFiles" function in Part 1.
 
import Test.Test_tbl
 
 
---------------------------------
 
-- Connect to a DSN through ODBC
 
withDB dsn = (connect driver) [ ("dsn",dsn) ]
 
 
---------------------------------
 
-- Get all the rows from the test table
 
getSomeData :: Database -> IO [(Int,Maybe Int)]
 
getSomeData db = do
 
let q = do
 
t <- table test_tbl
 
order [desc t c11]
 
return t
 
rs <- query db q
 
return $ map (\row -> (row!c11, row!c12)) rs
 
 
---------------------------------
 
main = do
 
-- Query the database
 
rs <- withDB "testdsn" $ \db -> getSomeData db
 
putStrLn $ foldl (\str (a,b) -> str ++ "(" ++ (show a) ++ "," ++ (show b) ++ ")\n") "" rs
 
</haskell>
 
 
For more examples, see [http://haskelldb.sourceforge.net/getting-started.html Getting Started] and [http://haskelldb.sourceforge.net/guide/ Guide to Hacking].
 
 
=== ICS Wiki (FIXME: links seem broken) ===
 
[http://abaris.zoo.cs.uu.nl:8080/wiki/ ICS Wiki] is a huge resource of Haskell materials (among others).
 
* [http://abaris.zoo.cs.uu.nl:8080/wiki/pub/Afp/DomainSpecificLanguages/haskelldb.pdf Database programming with HaskellDB] -- a PDF file (slides). A webpage containing a link to it (among others): the bottom (attachment part) of [http://abaris.zoo.cs.uu.nl:8080/wiki/Afp/DomainSpecificLanguages the ''Domain Specific Languages'' page of ICS Wiki].
 
* There are other links to HaskellDB materials in the [http://abaris.zoo.cs.uu.nl:8080/wiki/Afp/DomainSpecificLanguages#4_Haskell_DB HaskellDB section of the same page].
 
 
=== Other ===
 
* [http://www.vimeo.com/1983774 HaskellDB Talk Trailer]
 
* [http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=8F1C49953E49974D927950052C15CA41?doi=10.1.1.26.6906&rep=rep1&type=pdf Original HaskellDB paper]
 
 
== Future ==
 
 
[http://homepages.cwi.nl/~ralf/HList/ HList --- a Haskell library for strongly typed heterogeneous collections] includes also extensible records. Its relatedness to database programming is described in the articles, see also its [http://hackage.haskell.org/trac/summer-of-code/ticket/33 possible] relatedness to HaskellDB project.
 
 
To explore other declarative, type safe database managament approaches, see [[../CoddFish|CoddFish]]. Also it uses [http://homepages.cwi.nl/~ralf/HList/ HList].
 
 
== Related concepts ==
 
 
Concepts which are concerned by the papers of the two official HaskellDB homes
 
* [[Extensible record]]
 
* [[Phantom type]]
 
* [[Generalised algebraic datatype]]
 
* [[Relational algebra]]
 

Revision as of 14:50, 13 September 2010

1 Introduction

A combinator library for declarative, type safe database management. All queries and operations can be expressed in Haskell. No SQL need be written!

Hackage hosts the latest release of HaskellDB. The project home page can be found at http://trac.haskell.org/haskelldb.

1.1 Archived Information

Archive information from this page can be found on Applications and libraries/Database interfaces/HaskellDB/Archive.