How do you define relationships between data types?
Well, why is it any different from other fields? From one of your examples
[1], I'd expect you to have a list of questions in the Quiz data type, and
if necessary, a quiz field in the Question data type. This might be a bit
tricky but certainly achievable [2].
Something like the following:
data Quiz = Quiz {
description :: String,
subject :: String,
questions :: [Question]
} deriving (Show, Read)
data Question = Question {
title :: String,
choiceA :: String,
choiceB :: String,
choiceC :: String,
quiz :: Quiz
} deriving (Show, Read)
[1] http://github.com/chriseidhof/persist/blob/master/examples/Model.phs
[2] http://www.haskell.org/haskellwiki/Tying_the_Knot
On 28 September 2010 16:13, Chris Eidhof
Hey Jonathan,
I've done some work on this. The hard part is defining relationships between datatypes: how do you model this in Haskell? I've some code on github: http://github.com/chriseidhof/persist, you might be interested in that.
-chris
On 25 sep 2010, at 21:31, Jonathan Geddes wrote:
Cafe,
HaskellDB takes a database schema and produces Haskell data structures (plus some other query-related stuff for its EDSL query language).
What I'm looking for is the inverse of this functionality. I want to create tables based on a Haskell data structure with a few simple rules. These rules include: if a field is not of the form `Maybe a' then it can't be nullable in the database. If a field is not a primitive (in the database) then it is actually stored in another table and a reference id is stored in the table. Tables are produced recursively, unless they already exist, etc.
The HaskellDB approach is great for interfacing with existing tables, but in my case I already have data structures and now I would like a quick way to create tables to persist them.
Does such a thing exist? If not, would you find it useful? I may take this up as a side project if it does not already exist and others would find it useful.
Thanks,
--Jonathan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
-- Ozgur Akgun