haskelldb-users — For questions, suggestions, bug reports and patches

Re: [Haskelldb-users] Using Integer instead of Ints in dbToDBSpec

[Justin B. <jgb...@gm...>]

You should write your own. There is a program included (might even be
dbToDBSpec) that people always ask how to make do one thing or
another. It's a lot easier to look at how that program is written and
create your own for your own needs.

On Thu, Mar 19, 2009 at 7:10 PM, Dean Michael Berris
<mik...@gm...> wrote:
> Hi Guys,
>
> (Sorry if there are too many questions, I can't seem to find the
> answers easily anywhere else...)
>
> How do I make 'dbToDBSpec' create DBInfo's that don't use 'Int' but
> rather just 'Integer's for numeric non-floating-point fields?
>
> TIA
>
> --
> Dean Michael Berris | Software Engineer, Friendster, Inc.
> blog.cplusplus-soup.com | twitter.com/mikhailberis |
> linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
> deanberris.com
>
> ------------------------------------------------------------------------------
> Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are
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> easily build your RIAs with Flex Builder, the Eclipse(TM)based development
> software that enables intelligent coding and step-through debugging.
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[Haskelldb-users] Using Integer instead of Ints in dbToDBSpec

[Dean M. B. <mik...@gm...>]

Hi Guys,

(Sorry if there are too many questions, I can't seem to find the
answers easily anywhere else...)

How do I make 'dbToDBSpec' create DBInfo's that don't use 'Int' but
rather just 'Integer's for numeric non-floating-point fields?

TIA

-- 
Dean Michael Berris | Software Engineer, Friendster, Inc.
blog.cplusplus-soup.com | twitter.com/mikhailberis |
linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
deanberris.com

Re: [Haskelldb-users] Error Handling

[Dean M. B. <mik...@gm...>]

On Fri, Mar 20, 2009 at 8:04 AM, Justin Bailey <jgb...@gm...> wrote:
> Check out handleSql on the HDBC documentation
>
>  http://hackage.haskell.org/packages/archive/HDBC/2.1.0/doc/html/Database-HDBC.html#v%3AhandleSql
>

Thanks for the link! This definitely helps. :)

-- 
Dean Michael Berris | Software Engineer, Friendster, Inc.
blog.cplusplus-soup.com | twitter.com/mikhailberis |
linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
deanberris.com

Re: [Haskelldb-users] Error Handling

[Justin B. <jgb...@gm...>]

Check out handleSql on the HDBC documentation

 http://hackage.haskell.org/packages/archive/HDBC/2.1.0/doc/html/Database-HDBC.html#v%3AhandleSql

On Thu, Mar 19, 2009 at 5:00 PM, Dean Michael Berris
<mik...@gm...> wrote:
> On Fri, Mar 20, 2009 at 7:06 AM, Justin Bailey <jgb...@gm...> wrote:
>> You may be able to use the error handling provided by the underlying
>> library. However, that may not work. You may have more luck using
>> HaskellDB to generate SQL for you, which you execute directly using
>> your DB provider. That's how I've used it in the past, at least.
>>
>
> Hmmm... not quite the answer I was looking for... But at any rate, the
> program does exit with an SqlError -- I'm using the HDBC.ODBC backend,
> is there a way for me to inspect that object properly at some point in
> the program?
>
> --
> Dean Michael Berris | Software Engineer, Friendster, Inc.
> blog.cplusplus-soup.com | twitter.com/mikhailberis |
> linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
> deanberris.com
>

Re: [Haskelldb-users] Error Handling

[Dean M. B. <mik...@gm...>]

On Fri, Mar 20, 2009 at 7:06 AM, Justin Bailey <jgb...@gm...> wrote:
> You may be able to use the error handling provided by the underlying
> library. However, that may not work. You may have more luck using
> HaskellDB to generate SQL for you, which you execute directly using
> your DB provider. That's how I've used it in the past, at least.
>

Hmmm... not quite the answer I was looking for... But at any rate, the
program does exit with an SqlError -- I'm using the HDBC.ODBC backend,
is there a way for me to inspect that object properly at some point in
the program?

-- 
Dean Michael Berris | Software Engineer, Friendster, Inc.
blog.cplusplus-soup.com | twitter.com/mikhailberis |
linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
deanberris.com

Re: [Haskelldb-users] Error Handling

[Justin B. <jgb...@gm...>]

You may be able to use the error handling provided by the underlying
library. However, that may not work. You may have more luck using
HaskellDB to generate SQL for you, which you execute directly using
your DB provider. That's how I've used it in the past, at least.

On Thu, Mar 19, 2009 at 4:00 PM, Dean Michael Berris
<mik...@gm...> wrote:
> Hi Guys,
>
> Any pointers on how I should handle errors from the queries I execute?
> Does HaskellDB throw any exceptions? How should I recover from errors
> that happen from within the suggested 'withDB' combinator?
>
> TIA
>
> --
> Dean Michael Berris | Software Engineer, Friendster, Inc.
> blog.cplusplus-soup.com | twitter.com/mikhailberis |
> linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
> deanberris.com
>
> ------------------------------------------------------------------------------
> Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are
> powering Web 2.0 with engaging, cross-platform capabilities. Quickly and
> easily build your RIAs with Flex Builder, the Eclipse(TM)based development
> software that enables intelligent coding and step-through debugging.
> Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com
> _______________________________________________
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>

[Haskelldb-users] Error Handling

[Dean M. B. <mik...@gm...>]

Hi Guys,

Any pointers on how I should handle errors from the queries I execute?
Does HaskellDB throw any exceptions? How should I recover from errors
that happen from within the suggested 'withDB' combinator?

TIA

-- 
Dean Michael Berris | Software Engineer, Friendster, Inc.
blog.cplusplus-soup.com | twitter.com/mikhailberis |
linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
deanberris.com

Re: [Haskelldb-users] 'cabal install haskelldb-hsql' fails looking for old-time

[Dean M. B. <mik...@gm...>]

On Thu, Mar 19, 2009 at 11:39 PM, Justin Bailey <jgb...@gm...> wrote:
> You want to add old-time as a dependency in the cabal file for
> haskelldb-hsql. Word of caution - hsql isn't very well maintained, I dont
> think. You are better going with HDBC.
>

Thanks. So I have to hack it manually?

My problem with ODBC in general is that I've been running into
problems where the MySQL ODBC driver doesn't do auto-reconnection
properly. Explicitly opening and closing connections causes my Haskell
application to crash for some reason with a segmentation fault.

Debugging ODBC errors is no fun too, so that's why I'm looking around
for an alternative.

Thanks again, hopefully I can get that to work somehow and see if I
get farther with HSQL instead of HDBC.

-- 
Dean Michael Berris | Software Engineer, Friendster, Inc.
blog.cplusplus-soup.com | twitter.com/mikhailberis |
linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
deanberris.com

Re: [Haskelldb-users] 'cabal install haskelldb-hsql' fails looking for old-time

[Justin B. <jgb...@gm...>]

You want to add old-time as a dependency in the cabal file for
haskelldb-hsql. Word of caution - hsql isn't very well maintained, I dont
think. You are better going with HDBC.

On Thu, Mar 19, 2009 at 8:08 AM, Dean Michael Berris <mik...@gm...
> wrote:

> Hi Guys,
>
> I get this when I do 'cabal install haskelldb-hsql':
>
> Resolving dependencies...
> [1 of 1] Compiling Main             (
> /tmp/haskelldb-hsql-0.101938/haskelldb-hsql-0.10/Setup.hs,
> /tmp/haskelldb-hsql-0.101938/haskelldb-hsql-0.10/dist/setup/Main.o )
> Linking /tmp/haskelldb-hsql-0.101938/haskelldb-hsql-0.10/dist/setup/setup
> ...
> Configuring haskelldb-hsql-0.10...
> Warning: No 'build-type' specified. If you do not need a custom Setup.hs or
> ./configure script then use 'build-type: Simple'.
> Preprocessing library haskelldb-hsql-0.10...
> Building haskelldb-hsql-0.10...
>
> Database/HaskellDB/HSQL.hs:25:7:
>    Could not find module `System.Time':
>      it is a member of package old-time-1.0.0.1, which is hidden
> cabal: Error: some packages failed to install:
> haskelldb-hsql-0.10 failed during the building phase. The exception was:
> exit: ExitFailure 1
>
> Anything I can do to get this fixed? Running 'ghc-pkg describe
> old-time' yields this:
>
> name: old-time
> version: 1.0.0.1
> license: BSD3
> copyright:
> maintainer: lib...@ha...
> stability:
> homepage:
> package-url:
> description: This package provides the old time library.
>             For new code, the new time library is recommended.
> category: System
> author:
> exposed: True
> exposed-modules: System.Time
> hidden-modules:
> import-dirs: /usr/lib64/ghc-6.10.1/old-time-1.0.0.1
> library-dirs: /usr/lib64/ghc-6.10.1/old-time-1.0.0.1
> hs-libraries: HSold-time-1.0.0.1
> extra-libraries:
> extra-ghci-libraries:
> include-dirs: /usr/lib64/ghc-6.10.1/old-time-1.0.0.1/include
> includes: HsTime.h
> depends: base-4.0.0.0 old-locale-1.0.0.1
> hugs-options:
> cc-options:
> ld-options:
> framework-dirs:
> frameworks:
> haddock-interfaces:
> /usr/share/doc/ghc-6.10.1/libraries/old-time/old-time.haddock
> haddock-html: /usr/share/doc/ghc-6.10.1/libraries/old-time
>
> Am I missing anything obvious?
>
> TIA
>
> --
> Dean Michael Berris | Software Engineer, Friendster, Inc.
> blog.cplusplus-soup.com | twitter.com/mikhailberis |
> linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
> deanberris.com
>
>
> ------------------------------------------------------------------------------
> Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are
> powering Web 2.0 with engaging, cross-platform capabilities. Quickly and
> easily build your RIAs with Flex Builder, the Eclipse(TM)based development
> software that enables intelligent coding and step-through debugging.
> Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com
> _______________________________________________
> Haskelldb-users mailing list
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>

[Haskelldb-users] 'cabal install haskelldb-hsql' fails looking for old-time

[Dean M. B. <mik...@gm...>]

Hi Guys,

I get this when I do 'cabal install haskelldb-hsql':

Resolving dependencies...
[1 of 1] Compiling Main             (
/tmp/haskelldb-hsql-0.101938/haskelldb-hsql-0.10/Setup.hs,
/tmp/haskelldb-hsql-0.101938/haskelldb-hsql-0.10/dist/setup/Main.o )
Linking /tmp/haskelldb-hsql-0.101938/haskelldb-hsql-0.10/dist/setup/setup ...
Configuring haskelldb-hsql-0.10...
Warning: No 'build-type' specified. If you do not need a custom Setup.hs or
./configure script then use 'build-type: Simple'.
Preprocessing library haskelldb-hsql-0.10...
Building haskelldb-hsql-0.10...

Database/HaskellDB/HSQL.hs:25:7:
    Could not find module `System.Time':
      it is a member of package old-time-1.0.0.1, which is hidden
cabal: Error: some packages failed to install:
haskelldb-hsql-0.10 failed during the building phase. The exception was:
exit: ExitFailure 1

Anything I can do to get this fixed? Running 'ghc-pkg describe
old-time' yields this:

name: old-time
version: 1.0.0.1
license: BSD3
copyright:
maintainer: lib...@ha...
stability:
homepage:
package-url:
description: This package provides the old time library.
             For new code, the new time library is recommended.
category: System
author:
exposed: True
exposed-modules: System.Time
hidden-modules:
import-dirs: /usr/lib64/ghc-6.10.1/old-time-1.0.0.1
library-dirs: /usr/lib64/ghc-6.10.1/old-time-1.0.0.1
hs-libraries: HSold-time-1.0.0.1
extra-libraries:
extra-ghci-libraries:
include-dirs: /usr/lib64/ghc-6.10.1/old-time-1.0.0.1/include
includes: HsTime.h
depends: base-4.0.0.0 old-locale-1.0.0.1
hugs-options:
cc-options:
ld-options:
framework-dirs:
frameworks:
haddock-interfaces:
/usr/share/doc/ghc-6.10.1/libraries/old-time/old-time.haddock
haddock-html: /usr/share/doc/ghc-6.10.1/libraries/old-time

Am I missing anything obvious?

TIA

-- 
Dean Michael Berris | Software Engineer, Friendster, Inc.
blog.cplusplus-soup.com | twitter.com/mikhailberis |
linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
deanberris.com

Re: [Haskelldb-users] Segfault, in Linux when performing multiple connections over ODBC

[Justin B. <jgb...@gm...>]

Are you using the latest HDBC from Hackage? If not, upgrade to it and
see if the problem goes away. If that doesn't help, your best bet is
to go through the HDBC people - haskelldb just uses  HDBC, it doesn't
do anything special with it.

On Wed, Mar 18, 2009 at 9:43 AM, Dean Michael Berris
<mik...@gm...> wrote:
> Hi,
>
> I've recently found out that there was a subtle issue with opening and
> closing multiple connections in the same application context to the
> same data source over HaskellDB.HDBC.ODBC.
>
> I use unix-odbc and the MySQL 5 ODBC adaptor that comes with Gentoo
> Linux (updated to latest 2008 release) -- I've also upgraded to GHC
> 6.10.1 and subsequently wrote an application that (by mistake
> initially) created and destroyed connections to the ODBC layer. This
> caused the manifestation of a segmentation fault.
>
> I cannot post the whole code which causes the crash, but I can try and
> reproduce with another test case.
>
> Is this a known problem?
>
> Thanks and have a great day everyone.
>
> --
> Dean Michael Berris | Software Engineer, Friendster, Inc.
> blog.cplusplus-soup.com | twitter.com/mikhailberis |
> linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
> deanberris.com
>
> ------------------------------------------------------------------------------
> Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are
> powering Web 2.0 with engaging, cross-platform capabilities. Quickly and
> easily build your RIAs with Flex Builder, the Eclipse(TM)based development
> software that enables intelligent coding and step-through debugging.
> Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com
> _______________________________________________
> Haskelldb-users mailing list
> Has...@li...
> https://lists.sourceforge.net/lists/listinfo/haskelldb-users
>

[Haskelldb-users] Segfault, in Linux when performing multiple connections over ODBC

[Dean M. B. <mik...@gm...>]

Hi,

I've recently found out that there was a subtle issue with opening and
closing multiple connections in the same application context to the
same data source over HaskellDB.HDBC.ODBC.

I use unix-odbc and the MySQL 5 ODBC adaptor that comes with Gentoo
Linux (updated to latest 2008 release) -- I've also upgraded to GHC
6.10.1 and subsequently wrote an application that (by mistake
initially) created and destroyed connections to the ODBC layer. This
caused the manifestation of a segmentation fault.

I cannot post the whole code which causes the crash, but I can try and
reproduce with another test case.

Is this a known problem?

Thanks and have a great day everyone.

-- 
Dean Michael Berris | Software Engineer, Friendster, Inc.
blog.cplusplus-soup.com | twitter.com/mikhailberis |
linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis |
deanberris.com

[Haskelldb-users] Semantics of Empty / optimization

[Michael S. <sp...@de...>]

Hi there,

I'm really a user of HaskellDB, but am trying to mine the source code
for my own work.  In reviewing the optimizations, I've stumbled upon
this code:

removeEmpty
        = foldPrimQuery (Empty, BaseTable, project, restrict, binary, group, special)
        where
          -- Messes up queries without a table, e.g. constant queries
	  -- disabled by Bjorn Bringert 2004-04-08
          --project assoc Empty   = Empty
          project assoc query   | null assoc    = Empty
                                | otherwise     = Project assoc query

I'm wondering this is true: My understanding of Empty is that it
represents a nullary relation with a single element.  (This is necessary
to it can be the identity wrt. cartesian product, I think.)  If that's
the case, this transformation is incorrect, as `project [] query' should
return as many rows as query, not just one.  Or am I overlooking
something?

-- 
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla

Re: [Haskelldb-users] HDBC.ODBC, MySQL, connection string validity

[Justin B. <jgb...@gm...>]

I've applied your patch and uploaded a new release of HaskellDB to
hackage - 0.12. I also uploaded a new release of each HDBC driver so
they work with HDBC v2. Thanks Artyom for your patches in that area!

2009/2/10 Artyom Shalkhakov <art...@gm...>:
> Hello,
>
> I have successfully built HaskellDB and it's HDBC driver (using the version in
> darcs); some queries can be performed, but I noticed that sometimes MySQL
> ODBC fails with strange errors ("database not selected", etc.).
>
> I don't know whether it's a bug in MySQL driver or not, but if one
> replaces spaces
> with ";" when constructing connection string out of key-value pairs, everything
> works correctly.
>
> I can submit a patch fixing this. Is anybody interested?
>
> Cheers,
> Artyom Shalkhakov.
>
> ------------------------------------------------------------------------------
> Create and Deploy Rich Internet Apps outside the browser with Adobe(R)AIR(TM)
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Re: [Haskelldb-users] HDBC.ODBC, MySQL, connection string validity

[Artyom S. <art...@gm...>]

Hello,

2009/2/10 Justin Bailey <jgb...@gm...>:
> Please do. I have commit rights to the repo and will apply your patch ...

Okay, here it is (attached).

I've updated HDBC, HDBC-ODBC and HDBC-Sqlite3 backends so they compile
with the latest HDBC (2.1.0 as of this writing). I haven't tested
Sqlite3, though.

Also, can anybody tell me why documentation is so scarce, isn't HaskellDB
a good thing to use? Also, HaskellDB seems dead (like Lisp, which is dead
but living :)).

Cheers,
Artyom Shalkhakov.

Re: [Haskelldb-users] HDBC.ODBC, MySQL, connection string validity

[Justin B. <jgb...@gm...>]

Please do. I have commit rights to the repo and will apply your patch ...

On Tue, Feb 10, 2009 at 3:20 AM, Artyom Shalkhakov <
art...@gm...> wrote:

> Hello,
>
> I have successfully built HaskellDB and it's HDBC driver (using the version
> in
> darcs); some queries can be performed, but I noticed that sometimes MySQL
> ODBC fails with strange errors ("database not selected", etc.).
>
> I don't know whether it's a bug in MySQL driver or not, but if one
> replaces spaces
> with ";" when constructing connection string out of key-value pairs,
> everything
> works correctly.
>
> I can submit a patch fixing this. Is anybody interested?
>
> Cheers,
> Artyom Shalkhakov.
>
>
> ------------------------------------------------------------------------------
> Create and Deploy Rich Internet Apps outside the browser with
> Adobe(R)AIR(TM)
> software. With Adobe AIR, Ajax developers can use existing skills and code
> to
> build responsive, highly engaging applications that combine the power of
> local
> resources and data with the reach of the web. Download the Adobe AIR SDK
> and
> Ajax docs to start building applications today-
> http://p.sf.net/sfu/adobe-com
> _______________________________________________
> Haskelldb-users mailing list
> Has...@li...
> https://lists.sourceforge.net/lists/listinfo/haskelldb-users
>

[Haskelldb-users] HDBC.ODBC, MySQL, connection string validity

[Artyom S. <art...@gm...>]

Hello,

I have successfully built HaskellDB and it's HDBC driver (using the version in
darcs); some queries can be performed, but I noticed that sometimes MySQL
ODBC fails with strange errors ("database not selected", etc.).

I don't know whether it's a bug in MySQL driver or not, but if one
replaces spaces
with ";" when constructing connection string out of key-value pairs, everything
works correctly.

I can submit a patch fixing this. Is anybody interested?

Cheers,
Artyom Shalkhakov.

Re: [Haskelldb-users] Trying to build with ghc 6.10 : Is haskelldb still maintained ?

[Laurent G. <ml...@ni...>]

Thanks for your answers Justin.

On Dec 15, 2008, at 18:23, Justin Bailey wrote:
> On Sun, Dec 14, 2008 at 9:16 AM, Laurent Giroud <ml...@ni...> wrote:
>> However, it is not possible for me to compile haskelldb-dynamic,  
>> which
>> seems necessary to get the DBDirect program which analyzes the
>> database. This is something that I inferred from my research on the
>> web since the current documentation (or lack thereof) seems totally
>> obsolete on that matter.
>
> It's probably easier to write your own "DBDirect" like program than
> use the one in the distribution.


I don't know if I can do that yet, but I'll give it a try if I fail to  
build it.

>> Moreover, I also failed at building a working driver, be it for hdbc,
>> hsql (which seems utterly dead and unmaintained): hdbc-odbc doesn't
>> build either since Setup.hs wants to use a function which is now
>> obsolete.
>
> I am on Windows and have used HDBC-postgres successfully with  
> haskelldb.

Since I am on mac os x, I started with MySQL which is somehow  
"officially" supported by Apple, but it's a good idea indeed, I'll try  
it if I can't get anything to connect with MySQL.

>> Are there any plan to update haskelldb so it builds again with cabal
>> 1.6 and the recent versions of the modules it depends on or is this
>> library not maintained anymore ?
>
> haskelldb hasn't seen a lot of love lately, but people do still commit
> fixes. But as you have found it, it's not updated very frequently. If

Do you have any idea of why people submit patches but nobody ends up  
updating the version on hackage ?

> If
> you can get it building though, it's a pretty neat library. I used it
> to generate SQL queries and then executed those separately, but even
> for that it was a great library.

It seems to be a great library indeed, that's why I was a bit  
surprised to see that the hackage version did not build: it would seem  
to me that it was by far the most interesting of the database library  
available on Haskell. SQL type safety is such a great feature that I  
thought nobody would want to use anything but that, apparently I was  
wrong since the other database libraries (hdbc, takusen) seem to be  
more active than haskelldb is.

Thanks again for your reply !

Cheers,
Laurent

Re: [Haskelldb-users] Trying to build with ghc 6.10 : Is haskelldb still maintained ?

[Justin B. <jgb...@gm...>]

On Sun, Dec 14, 2008 at 9:16 AM, Laurent Giroud <ml...@ni...> wrote:
> However, it is not possible for me to compile haskelldb-dynamic, which
> seems necessary to get the DBDirect program which analyzes the
> database. This is something that I inferred from my research on the
> web since the current documentation (or lack thereof) seems totally
> obsolete on that matter.

It's probably easier to write your own "DBDirect" like program than
use the one in the distribution.

> Moreover, I also failed at building a working driver, be it for hdbc,
> hsql (which seems utterly dead and unmaintained): hdbc-odbc doesn't
> build either since Setup.hs wants to use a function which is now
> obsolete.

I am on Windows and have used HDBC-postgres successfully with haskelldb.

> Are there any plan to update haskelldb so it builds again with cabal
> 1.6 and the recent versions of the modules it depends on or is this
> library not maintained anymore ?

haskelldb hasn't seen a lot of love lately, but people do still commit
fixes. But as you have found it, it's not updated very frequently. If
you can get it building though, it's a pretty neat library. I used it
to generate SQL queries and then executed those separately, but even
for that it was a great library.

Justin

[Haskelldb-users] Trying to build with ghc 6.10 : Is haskelldb still maintained ?

[Laurent G. <ml...@ni...>]

Hi,

I have been trying to build a working version of haskelldb from the  
packages available on hackage but couldn't manage to obtain one so far.

All packages I have tried required some adaptations for ghc 6.10.1 and  
I managed to build the following ones:

haskelldb-0.10
haskelldb-flat-0.10
haskelldb-hdbc-0.10

However, it is not possible for me to compile haskelldb-dynamic, which  
seems necessary to get the DBDirect program which analyzes the  
database. This is something that I inferred from my research on the  
web since the current documentation (or lack thereof) seems totally  
obsolete on that matter.

It fails because the package depends on the plugins package which  
can't be build with anything but cabal 1.4. Having ghc 6.10.1 with  
cabal 1.6 and not enough haskell skills I am completely stuck there.

It looks like installing ghc 6.8 or 6.6 with cabal 1.4 might help  
building everything properly but it wouldn't make much sense to work  
with an environment which by all standards is obsolete.

Moreover, I also failed at building a working driver, be it for hdbc,  
hsql (which seems utterly dead and unmaintained): hdbc-odbc doesn't  
build either since Setup.hs wants to use a function which is now  
obsolete.

I found that the code on http://code.haskell.org/haskelldb seems  
fresher than what is on hackage, but still couldn't build it...

Are there any plan to update haskelldb so it builds again with cabal  
1.6 and the recent versions of the modules it depends on or is this  
library not maintained anymore ?

My haskell capabilities do not allow me to do more than fix a few  
cabal broken dependencies unfortunately so I'd like to know if there's  
still hope that these problem can be fixed. I have been advised to try  
other database interfaces, such as HDBC or Takusen however they are  
very classic SQL wrappers which bring nothing more than what I can  
find for C++ or any other language out there...

Thanks in advance for any hints/information you might have.

Regards,
Laurent

[Haskelldb-users] GROUP BY bug fix

[Justin B. <jgb...@gm...>]

On Thu, Jul 10, 2008 at 12:04 AM, Henning Thielemann
<has...@he...> wrote:
>
> SELECT C2 C
> FROM (SELECT C C2
>       FROM POINTS T1
>       GROUP BY C2) T1
>
>
> But the C2 after GROUP BY does not denote a column of a table. It may be
> replaced by C or the GROUP BY may be moved to the outer SELECT statement.
>

I've corrected this bug in the attached patch. It occurred because the
defaultSqlGroup function in Database.HaskellDB.Sql.Default did not
properly filter projected columns from its group by clause. I also
fixed a bug in defaultSqlProject where order by columns were not added
to the group by clause if they did not appear in a projection.

I added a few tests for the new cases which appear to work. Any
comments welcome!

Justin

[Haskelldb-users] Converting BoundedString to String

[Justin B. <jgb...@gm...>]

I have run into a problem several times where I have a column that is
defined as Expr BStr10 (or similar) and I want to convert it to a
string column, i.e. Expr String. I came up with a class declaration
and some instances that can do it, but is there a simpler way? I have
(which must be defined in Query.hs since it uses the Expr
constructor):

class BStrToStr s d where
  toStr :: s -> d

instance (Size n) => BStrToStr (Expr (BoundedString n)) (Expr String) where
  toStr (Expr e) = Expr e

instance (Size n) => BStrToStr (Expr (Maybe (BoundedString n))) (Expr
(Maybe String)) where
  toStr (Expr m) = Expr m

This toy example shows the class in action. "query" will compile fine,
but "queryX" will not (when uncommented). Any suggestions are welcome!

Justin

\begin{code}
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
import Database.HaskellDB
import Database.HaskellDB.DBLayout
import Database.HaskellDB.Query (Expr(..))
import Database.HaskellDB.BoundedList (Size)

query = do
 t <- table someTable
 project $ strField << (toStr (t ! bstrField) :: Expr String)

-- Below does not compile.
--
queryX = do
  t <- table someTable
  project $ strField << t ! bstrField

class BStrToStr s d where
  toStr :: s -> d

instance (Size n) => BStrToStr (Expr (BoundedString n)) (Expr String) where
  toStr (Expr e) = Expr e

instance (Size n) => BStrToStr (Expr (Maybe (BoundedString n))) (Expr
(Maybe String)) where
  toStr (Expr m) = Expr m

type SomeTable = (RecCons StrField (Expr String)
                   (RecCons BStrField (Expr BStr10) RecNil))

someTable :: Table SomeTable
someTable = baseTable "someTable" $
             hdbMakeEntry StrField #
             hdbMakeEntry BStrField

data StrField = StrField
instance FieldTag StrField where
    fieldName _ = "strField"

strField :: Attr StrField String
strField = mkAttr StrField

data BStrField = BStrField
instance FieldTag BStrField where
    fieldName _ = "bstrField"

bstrField :: Attr BStrField BStr10
bstrField = mkAttr BStrField

\end{code}

[Haskelldb-users] Patch for review: Template Haskell function for HaskellDB

[Justin B. <jgb...@gm...>]

All,

Attached you'll find a patch which adds several useful Template
Haskell functions to haskelldb. They are not intended to be part of
the base haskelldb install, so no new dependency on TH is introduced.
Instead, they are in a haskelldb-th directory under the haskelldb
source distribution, similar to how the driver files are distributed.
Building and installing the package is easy:

  cd haskelldb-th
  runhaskell Setup.hs configure
  runhaskell Setup.hs build
  runhaskell Setup.hs haddock
  runhaskell Setup.hs install

Only one module is exported at this time - Database.HaskellDB.CodeGen.
The functions exported are:

  mkField, mkFieldWithName, mkDBDirectField - Create compile-time
field declarations with various levels of control over names.
  mkDBDirectTable, mkDBDirectTableWithName, mkDBDirectTableType --
Create compile-time table declarations and  type synonyms, with
various degrees of control over names or individual piece.
  mkRecord - Provides a simpler way to build projections from multiple
tables and fields.

Comments and suggestions welcome! If this patch is accepted, I will
upload the package to hackage so it is available as a separate
download. Of course, it depends on haskelldb 0.11, so that will need
to be updated first.

Justin

p.s. haskelldb actually has some legacy functions in
test/old/THField.hs that are similar to these, but I discovered those
after I'd written mine, plus they aren't quite as robust.

Re: [Haskelldb-users] Sorting by the result of an expression

[Justin B. <jgb...@gm...>]

On Mon, Jul 21, 2008 at 11:47 AM, GrayShade <gra...@gm...> wrote:

> Is there any way to do something like
>                order [desc t (constant date' .-. date)]
>
> in HaskellDB (i. e. sorting by an expression, not by a column).
>

There isn't. You can create a column containing the expression you'd like to
sort by, though.

Justin

[Haskelldb-users] Sorting by the result of an expression

[GrayShade <gra...@gm...>]

Is there any way to do something like
		order [desc t (constant date' .-. date)]

in HaskellDB (i. e. sorting by an expression, not by a column).

Thanks.