htoolkit-users — HToolkit Users Forum

[htoolkit-users] HSQL patch

[Frederik E. <fre...@a5...>]

Hi,

I just added a new SqlBind instance to HSQL.hsc

instance SqlBind a => SqlBind (Maybe a)

which returns NULL values as Nothing. I needed this because I'm using
an algorithm that uses NULL values and I didn't want to have to call
getFieldValueMB all the time. Actually I'm using my own wrapper module
which uses heterogenous lists so handling NULL values through the type
system is just much more convenient for me:

http://ofb.net/~frederik/futility/src/HSQLExtras.hs

Anyway, it was a bit of work to add this. I had to add a new method to
the SqlBind class

	fromSqlCStringLen :: SqlType -> CString -> Int -> IO (Maybe a)
	fromSqlCStringLen sqlType cstr cstrLen =
            if cstr == nullPtr then return Nothing
            else fromNonNullSqlCStringLen sqlType cstr cstrLen

to be used instead of 

	fromNonNullSqlCStringLen :: SqlType -> CString -> Int -> IO (Maybe a)

This is because apparently NULL values originally get into the system
as nullPtr's, so SqlBind needs to be able to know about those
nullPtr's in order to process NULL values.

Now getFieldValueMB passes fromSqlCStringLen rather than
fromNonNullSqlCStringLen to the driver. The drivers have to be updated
to make use of this feature - currently they intercept NULL values and
return Nothing, but they have to be changed so that they pass these
along to value extractor (which will return Just Nothing in the case
of my new instance). If they aren't changed, the old behavior will
just be preserved so it's *not* necessary to change all of them at
once. I updated MySQL (tested) and PostgreSQL (not tested), so you can
see what has to be done.

Now I can write something like this (it uses another wrapper,
http://ofb.net/~frederik/futility/src/DBTool.hs)

    query0 (sql "insert into $bar values (2,null)")
    Just ((a::Maybe Int) :. (b::Maybe Int) :. Nil) <- query1 (sql "select * from $bar limit 1")
    print (a,b)

==> (Just 2,Nothing)

I hope this patch is suitable. If it isn't accepted then I'll have to
create my own fork of the library, because I depend on this feature in
other stuff I'm distributing.

Cheers,

Frederik

Re: [htoolkit-users] HSQL 1.6 only returning

[Mark W. <mwa...@bi...>]

A call is being made to set SQL_ATTR_ROW_ARRAY_SIZE to 2 however this is =
only compiled in if MSSQL_ODBC is defined which it was in the Setup.lhs =
that I had.=20

I can't access CVS to confirm if this is in the main source tree or why =
it was put in.

Cheers

Mark
  ----- Original Message -----=20
  From: Mark Wassell=20
  To: hto...@li...=20
  Sent: Tuesday, November 01, 2005 9:12 PM
  Subject: [htoolkit-users] HSQL 1.6 only returning


  Hi,

  I am using HSQL 1.6 with ODBC to a MySQL database on Windows XP. When =
I do a query only every other row is being returned (ie only half of the =
rows).=20

  Does anyone have any idea what might be going on? I don't have a =
problem using Ruby.

  The code is based on the example code:

  retrieveRecords :: Connection -> IO [[String]]
  retrieveRecords c =3D do
   query c "select * from treenode " >>=3D collectRows getRow
   where
    getRow :: Statement -> IO [String]
    getRow stmt =3D do
     f1           <- (getFieldValue stmt "id")
     return [show (f1::Int)]


  main =3D handleSql print $ do
   bracket (connect datasource user_id password) disconnect $ \c ->
       inTransaction c $ \c -> do
                 rs <- retrieveRecords c
          mapM print rs
          putStrLn ""

  Cheers

  Mark

[htoolkit-users] HSQL 1.6 only returning

[Mark W. <mwa...@bi...>]

Hi,

I am using HSQL 1.6 with ODBC to a MySQL database on Windows XP. When I =
do a query only every other row is being returned (ie only half of the =
rows).=20

Does anyone have any idea what might be going on? I don't have a problem =
using Ruby.

The code is based on the example code:

retrieveRecords :: Connection -> IO [[String]]
retrieveRecords c =3D do
 query c "select * from treenode " >>=3D collectRows getRow
 where
  getRow :: Statement -> IO [String]
  getRow stmt =3D do
   f1           <- (getFieldValue stmt "id")
   return [show (f1::Int)]


main =3D handleSql print $ do
 bracket (connect datasource user_id password) disconnect $ \c ->
     inTransaction c $ \c -> do
               rs <- retrieveRecords c
        mapM print rs
        putStrLn ""

Cheers

Mark

Re: [htoolkit-users] HSQL

[Krasimir A. <ka2...@ya...>]

Hi John,

I can change Sqlite.hs to Sqlite2.hs in the next HSQL
release but unfortunatelly this wil break the existing
programs that use SQLite. I hope that they aren't too
much. HSQL already has SQLite3 driver.

Cheers,
  Krasimir

--- John Lask <jv...@ho...> wrote:

> recently used HSQL: and had to make some mods..
> fromSqlValue
> 
> also advise that you change name of sqlite module as
> under windows/hugs the 
> sqlite.dll (hugs c interface) will cause a name
> clash with sqlite.dll 
> (sqlite dll) - advise to change to something like
> sqlite2 as the sqlite3 dll 
> is incompatible and you might want to add sqlite3
> support at later stage.
> 
> in the export list of HSQL as then it is possible to
> define instances of 
> SqlBind outside of HSQL
> 
> JL.
> 
> 
> 
> 
>
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[htoolkit-users] HSQL

[John L. <jv...@ho...>]

recently used HSQL: and had to make some mods..
fromSqlValue

also advise that you change name of sqlite module as under windows/hugs the 
sqlite.dll (hugs c interface) will cause a name clash with sqlite.dll 
(sqlite dll) - advise to change to something like sqlite2 as the sqlite3 dll 
is incompatible and you might want to add sqlite3 support at later stage.

in the export list of HSQL as then it is possible to define instances of 
SqlBind outside of HSQL

JL.

Re: [htoolkit-users] HSQL connection syntax

[Krasimir A. <ka2...@ya...>]

You should read the driver documentation for this kind
of questions (e.g. MySQL and ODBC documentations). In
particular cases the MySQL server name is the DNS name
(or localhost). For "Connection string" or "Data
source name" you should read the ODBC documentation
where it is described how to create new data sources.

Cheers,
  Krasimir

--- Frederik Eaton <fre...@a5...> wrote:

> The driver-specific HSQL documentation which I have
> doesn't say what
> syntax should be used for "Server name" in MySQL (I
> assume this can
> point to a unix domain socket or specify a hostname
> with port..?) or
> for "Connection string" or "Data source name" in
> ODBC. Does anyone
> know what the syntax for these strings is?
> 
> Thanks,
> 
> Frederik
> 
>     Database.HSQL.MySQL
>     Description
>     Synopsis
>     connect :: String -> String -> String -> String
> -> IO Connection
>     module Database.HSQL
>     Documentation
>     connect
>     :: String        Server name
>     -> String        Database name
>     -> String        User identifier
>     -> String        Authentication string
> (password)
>     -> IO Connection
>     Makes a new connection to the database server.
> 
>     ---
> 
>     Database.HSQL.ODBC
>     Description
>     Synopsis
>     connect :: String -> String -> String -> IO
> Connection
>     driverConnect :: String -> IO Connection
>     module Database.HSQL
>     Documentation
>     connect
>     :: String        Data source name
>     -> String        User identifier
>     -> String        Authentication string
> (password)
>     -> IO Connection the returned value represents
> the new connection
>     Makes a new connection to the ODBC data source
>     driverConnect
>     :: String                  Connection string
>     -> IO Connection           the returned value
> represents the new connection
>     driverConnect is an alternative to connect. It
> supports data
>     sources that require more connection information
> than the three
>     arguments in connect and data sources that are
> not defined in the
>     system information.
> 
> 
> -- 
> http://ofb.net/~frederik/
> 
> 
>
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[htoolkit-users] erroneous error text

[Frederik E. <fre...@a5...>]

Hi,

When I try to cast the result of a 'sum' to Int, I get the following
error message:

The type of sum(a.s) field can't be converted to SqlDouble type

When I change the type to Double it goes away. So it looks like the
error message is reporting the type converted *from* and not the type
converted *to*. Maybe the text should be changed to e.g.

The type of sum(a.s) field can't be converted from SqlDouble to SqlInteger

Thanks,

Frederik

-- 
http://ofb.net/~frederik/

[htoolkit-users] HSQL connection syntax

[Frederik E. <fre...@a5...>]

The driver-specific HSQL documentation which I have doesn't say what
syntax should be used for "Server name" in MySQL (I assume this can
point to a unix domain socket or specify a hostname with port..?) or
for "Connection string" or "Data source name" in ODBC. Does anyone
know what the syntax for these strings is?

Thanks,

Frederik

    Database.HSQL.MySQL
    Description
    Synopsis
    connect :: String -> String -> String -> String -> IO Connection
    module Database.HSQL
    Documentation
    connect
    :: String        Server name
    -> String        Database name
    -> String        User identifier
    -> String        Authentication string (password)
    -> IO Connection
    Makes a new connection to the database server.

    ---

    Database.HSQL.ODBC
    Description
    Synopsis
    connect :: String -> String -> String -> IO Connection
    driverConnect :: String -> IO Connection
    module Database.HSQL
    Documentation
    connect
    :: String        Data source name
    -> String        User identifier
    -> String        Authentication string (password)
    -> IO Connection the returned value represents the new connection
    Makes a new connection to the ODBC data source
    driverConnect
    :: String                  Connection string
    -> IO Connection           the returned value represents the new connection
    driverConnect is an alternative to connect. It supports data
    sources that require more connection information than the three
    arguments in connect and data sources that are not defined in the
    system information.


-- 
http://ofb.net/~frederik/

Re: [htoolkit-users] Problems installing hsql 1.6 MySQL package

[tim <ti...@cs...>]

Hi Krasismir,

I removed all the cc options from MySQL.buildinfo
and evrything built and installed fine. I haven't
done any tests yet.

Thank you very much!
Tim

Krasimir Angelov schrieb:
> Hi Tim,
> 
> It looks like there is a bug in Cabal which is fixed
> in CVS. The problem is that the cc-options field in
> MySQL.buildinfo contains "-fomit-frame-pointer -pipe
> -march=i586 -mtune=pentiumpro" options. These options
> are incorrectly passed to hsc2hs which is a bug. The
> workaround is to remove manually these options. I
> think that after that you will be able to preprocess
> the hsc2hs scripts.
> 
> Cheers,
>   Krasimir
> 
> --- tim <ti...@cs...> wrote:
> 
> 


-- 
Tim Richter
Technischer Angestellter, Theoretische Informatik, Uni Potsdam
14482 Potsdam, August-Bebel-Str. 89, Haus 4, Zimmer 1.19
Tel.: 0331 977 3064
email: ti...@cs...

Re: [htoolkit-users] Problems installing hsql 1.6 MySQL package

[Krasimir A. <ka2...@ya...>]

Hi Tim,

Try to run Setup.lhs with -v option:

$ ./Setup.lhs build -v

and send me the generated output. Can you send me the
generated MySQL.buildinfo file?

Cheers,
  Krasimir

--- tim <ti...@cs...> wrote:

> Hello,
> 
> I'm rather new to Haskell, ghc, Cabal and all that.
> I'd very much like to do some CGI/HTML programming
> in Haskell using WASH and a MySQL Database. Since
> WASH
> doesn't support MySQL I thought I should give HSQL a
> try.
> 
> The hsql-1.6. package itself installed fine under
> ghc 6.4 on my PC
> running Mandriva 2005. But the mysql package has
> following problem:
> 
> tim@jered MySQL$ runghc Setup.lhs configure
> Warning: No license-file field.
> Configuring hsql-mysql-1.6...
> configure: searching for ghc in path.
> configure: found ghc at /usr/bin/ghc
> configure: looking for package tool: ghc-pkg near
> compiler in /usr/bin/ghc
> configure: found package tool in /usr/bin/ghc-pkg
> configure: Using install prefix: /usr/local
> configure: Using compiler: /usr/bin/ghc
> configure: Compiler flavor: GHC
> configure: Compiler version: 6.4
> configure: Using package tool: /usr/bin/ghc-pkg
> configure: No haddock found
> configure: No happy found
> configure: No alex found
> configure: Using hsc2hs: /usr/bin/hsc2hs
> configure: Using cpphs: /usr/local/bin/cpphs
> configure: Reading installed packages...
> configure: Dependency base-any: using base-1.0
> configure: Dependency hsql-any: using hsql-1.6
> configure: Using mysql_config: /usr/bin/mysql_config
> configure: configuring mysqlclient library
> 
> - so far, so good (or do I need some of haddock,
> happy, alex ... ?)
> 
> tim@jered MySQL$ runghc Setup.lhs build
> Preprocessing library hsql-mysql-1.6...
> unrecognized option `-f'
> unrecognized option `-p'
> unrecognized option `-m'
> unrecognized option `-a'
> unrecognized option `-r'
> unrecognized option `-m'
> unrecognized option `-f'
> unrecognized option `-n'
> Usage: hsc2hs [OPTIONS] INPUT.hsc [...]
>  
>   -o FILE          --output=FILE          name of
> main output file
>   -t FILE          --template=FILE        template
> file
> 
>  ... and so on ...
> 
> *** Exception: got error code while preprocessing:
> Database.HSQL.MySQL
> 
> I hope somebody of you sees at once what's going on
> and takes the time
> point it out to me.
> 
> Tim Richter
> 
> Computer Science
> University Potsdam
> Germany
> 
> 
> 
> 
> 
>
-------------------------------------------------------
> SF.Net email is sponsored by: Discover Easy Linux
> Migration Strategies
> from IBM. Find simple to follow Roadmaps,
> straightforward articles,
> informative Webcasts and more! Get everything you
> need to get up to
> speed, fast.
>
http://ads.osdn.com/?ad_id=7477&alloc_id=16492&op=click
> _______________________________________________
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> hto...@li...
>
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> 



		
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[htoolkit-users] Problems installing hsql 1.6 MySQL package

[tim <ti...@cs...>]

Hello,

I'm rather new to Haskell, ghc, Cabal and all that.
I'd very much like to do some CGI/HTML programming
in Haskell using WASH and a MySQL Database. Since WASH
doesn't support MySQL I thought I should give HSQL a try.

The hsql-1.6. package itself installed fine under ghc 6.4 on my PC
running Mandriva 2005. But the mysql package has following problem:

tim@jered MySQL$ runghc Setup.lhs configure
Warning: No license-file field.
Configuring hsql-mysql-1.6...
configure: searching for ghc in path.
configure: found ghc at /usr/bin/ghc
configure: looking for package tool: ghc-pkg near compiler in /usr/bin/ghc
configure: found package tool in /usr/bin/ghc-pkg
configure: Using install prefix: /usr/local
configure: Using compiler: /usr/bin/ghc
configure: Compiler flavor: GHC
configure: Compiler version: 6.4
configure: Using package tool: /usr/bin/ghc-pkg
configure: No haddock found
configure: No happy found
configure: No alex found
configure: Using hsc2hs: /usr/bin/hsc2hs
configure: Using cpphs: /usr/local/bin/cpphs
configure: Reading installed packages...
configure: Dependency base-any: using base-1.0
configure: Dependency hsql-any: using hsql-1.6
configure: Using mysql_config: /usr/bin/mysql_config
configure: configuring mysqlclient library

- so far, so good (or do I need some of haddock, happy, alex ... ?)

tim@jered MySQL$ runghc Setup.lhs build
Preprocessing library hsql-mysql-1.6...
unrecognized option `-f'
unrecognized option `-p'
unrecognized option `-m'
unrecognized option `-a'
unrecognized option `-r'
unrecognized option `-m'
unrecognized option `-f'
unrecognized option `-n'
Usage: hsc2hs [OPTIONS] INPUT.hsc [...]
 
  -o FILE          --output=FILE          name of main output file
  -t FILE          --template=FILE        template file

 ... and so on ...

*** Exception: got error code while preprocessing: Database.HSQL.MySQL

I hope somebody of you sees at once what's going on and takes the time
point it out to me.

Tim Richter

Computer Science
University Potsdam
Germany

[htoolkit-users] Installing hsql on ghc 6.4

[Robert v. H. <rh...@cs...>]

Hi all,

I am experiencing a problem with installing hsql on a Mac, with ghc 6.4.

Namely, during make install, it says:

/usr/local/bin/ghc-pkg -u -g -i hsql.pkg
Reading package info from "hsql.pkg" ghc-pkg: Line 1: Invalid syntax (no 
colon after field name)

I have attached the package.conf file from ghc.

The hsql.pkg file looks like this:

Package
    {name = "hsql",
     auto=True,
     import_dirs = ["/Users/rherk/soft/HSQL/lib/HSQL/GHC/imports"],
     source_dirs = [],
     library_dirs = 
["/Users/rherk/soft/HSQL/lib/HSQL/GHC","/Users/rherk/soft/mysql/lib/mysql"],
     hs_libraries = ["HSsql"],
     extra_libraries = ["mysqlclient","mysqlclient","m","z"],
     include_dirs = [],
     c_includes = [],
     package_deps = ["base"],
     extra_ghc_opts = [],
     extra_cc_opts = [],
     extra_ld_opts = [],
     framework_dirs = [],
     extra_frameworks = []
    }

Now, it may of course well be that it  is the package.conf file from the 
ghc 6.4 distribution that is wrong. If this is indeed the case, please 
tell me, so that I can contact them about this.

Regards,
Robert

Re: [htoolkit-users] Problem with HSQL

[Bjorn B. <d00...@dt...>]

Robert van Herk wrote:
> However, when I do ghci -package hsql, I get:
> Loading package base ... linking ... done.
> Loading package hsql ... ghc-6.2.2: can't load .so/.DLL for: c=20
> (/usr/lib/libc.so: invalid ELF header)

I belive you are the second person in the world to see this error. If=20
you Google for it, all you get is a log of me asking about it in the=20
#haskell irc channel. The problem is that for some reason, on some=20
machines mysql-config reports that it needs -lc. This means that=20
/usr/lib/ghc-6.2.2/package.conf will have "c" in extra_libraries, which=20
means that ghci will try to load libc.so. This is completely redundant,=20
and causes the error above. The simplest solution is to hand-edit=20
package.conf after installing HSQL and remove "c" from extra_libraries=20
in the hsql section. We should probably put a fix for this in the=20
configure script.

/Bj=F6rn

[htoolkit-users] Problem with HSQL

[Robert v. H. <rh...@cs...>]

Hi all,

I am experiencing a problem building HSQL on SuSE 9.2, GHC 6.2.2.

I checked out HSQL from cvs, did
 ./configure --enable-mysql --prefix=/home/robert/soft
 make install

This seemed to go perfectly. Configure told me
 MySQL:       yes
 PostgreSQL:  no
 SQLite:      no
 ODBC:        no
which was what I wanted.

However, when I do ghci -package hsql, I get:
 Loading package base ... linking ... done.
 Loading package hsql ... ghc-6.2.2: can't load .so/.DLL for: c 
(/usr/lib/libc.so: invalid ELF header)

Do you have any idea what might be wrong?

Thanks,
Robert

Re: [htoolkit-users] "commands out of sync"

[Frederik E. <fre...@a5...>]

> I guess that means that in a concurrent application I should use some
> other object to identify the main database internally than a
> connection, maybe an 'IO Connection'...?

Until I get "Too many connections". Sigh.

Re: [htoolkit-users] HSQL, HList

[Frederik E. <fre...@a5...>]

> If you already have an open result and try to run another query, you 
> will get an expcetion with the MySQL drivers.

OK, this was the subject of my other recent message.

> >What I'm seeing is that if I run closeStatement before reading all the
> >rows from a query, it goes ahead and reads the rest of the rows
> >silently, which is bad if there are millions of rows. For instance, if
> >there is an error, like if I request a field with the wrong type, then
> >since these are caught by a 'finally' clause in getFieldValue and
> >trigger a closeStatement, the error message isn't printed (by
> >'handleSql print' in main) until the whole table is read in, several
> >minutes later.
> 
> That doesn't seem like what you'd expect. Bug in the driver, or HSQL maybe?

I don't know, but the HSQL code looks like it's doing the right thing.
OTOH, MySQL should do better than that...

> >I'm trying to get MyODBC installed - this is necessary using MySQL
> >through ODBC, right? - to see if the behavior is any different, since
> >you seemed to imply it would be less problematic.
> 
> Well, yes and no. You don't get the exception like with the MySQL 
> driver, but the reason for that is that the MyODBC driver seems to fetch 
> the entire result set from the server straight away and keep it locally. 
> So you can have two open queries, but the only thing you gain from 
> laziness is that the data you never use will be in C code, not Haskell, 
> and thus take up less space. But that of course won't help if the 
> results are larger that you local RAM for example.

Ah, that's terrible. So I have no reason to use ODBC.

Frederik

-- 
http://ofb.net/~frederik/

[htoolkit-users] "commands out of sync"

[Frederik E. <fre...@a5...>]

Uing MySQL interface ... If I try to open two statements at once, i.e.
before closing the first one, then I get the error message "Commands
out of sync; you can't run this command now". It looks like a
limitation of libmysqlclient...

If I open multiple connections, it seems to work, is this the only way
to do concurrent queries?

I guess that means that in a concurrent application I should use some
other object to identify the main database internally than a
connection, maybe an 'IO Connection'...?

Frederik

-- 
http://ofb.net/~frederik/

Re: [htoolkit-users] HSQL, HList

[Bjorn B. <d00...@dt...>]

Frederik Eaton wrote:
>>You might want to be careful with collectRowsAsync. We have the same=20
>>thing in HaskellDB, and it turns out to be a problem with some database=
s=20
>>if you run a second query without getting all that data from the first=20
>>one. I think MySQL with the native drivers does it for example, but not=
=20
>>with ODBC.
>=20
> What are the symptoms?

If you already have an open result and try to run another query, you=20
will get an expcetion with the MySQL drivers.

> What I'm seeing is that if I run closeStatement before reading all the
> rows from a query, it goes ahead and reads the rest of the rows
> silently, which is bad if there are millions of rows. For instance, if
> there is an error, like if I request a field with the wrong type, then
> since these are caught by a 'finally' clause in getFieldValue and
> trigger a closeStatement, the error message isn't printed (by
> 'handleSql print' in main) until the whole table is read in, several
> minutes later.

That doesn't seem like what you'd expect. Bug in the driver, or HSQL mayb=
e?

> I'm trying to get MyODBC installed - this is necessary using MySQL
> through ODBC, right? - to see if the behavior is any different, since
> you seemed to imply it would be less problematic.

Well, yes and no. You don't get the exception like with the MySQL=20
driver, but the reason for that is that the MyODBC driver seems to fetch=20
the entire result set from the server straight away and keep it locally.=20
So you can have two open queries, but the only thing you gain from=20
laziness is that the data you never use will be in C code, not Haskell,=20
and thus take up less space. But that of course won't help if the=20
results are larger that you local RAM for example.

/Bj=F6rn

Re: [htoolkit-users] HSQL, HList

[Frederik E. <fre...@a5...>]

> You might want to be careful with collectRowsAsync. We have the same 
> thing in HaskellDB, and it turns out to be a problem with some databases 
> if you run a second query without getting all that data from the first 
> one. I think MySQL with the native drivers does it for example, but not 
> with ODBC.

What are the symptoms?

What I'm seeing is that if I run closeStatement before reading all the
rows from a query, it goes ahead and reads the rest of the rows
silently, which is bad if there are millions of rows. For instance, if
there is an error, like if I request a field with the wrong type, then
since these are caught by a 'finally' clause in getFieldValue and
trigger a closeStatement, the error message isn't printed (by
'handleSql print' in main) until the whole table is read in, several
minutes later.

I'm trying to get MyODBC installed - this is necessary using MySQL
through ODBC, right? - to see if the behavior is any different, since
you seemed to imply it would be less problematic.

Frederik

-- 
http://ofb.net/~frederik/

Re: [htoolkit-users] HSQL, HList

[Frederik E. <fre...@a5...>]

On Tue, Feb 22, 2005 at 10:18:03PM +0100, Bjorn Bringert wrote:
> Frederik Eaton wrote:
> >I wrote some functions which can be used with HSQL to make it a lot
> >more concise, using the HList concept:
> >
> >http://ofb.net/~frederik/SqlRow/
> >
> >If anybody wants to look at it and give feedback. Maybe it could be
> >incorporated into the library.
> 
> One difference to the current HSQL is that you access record fields by 
> position rather than by name. Not sure whether this is good or bad. One 
> problem is that there is as little type safety now as before, and it's 
> as easy to access a non-existing field.
> 
> The nice thing is that you can get back a whole row at a time, and I 
> like the pattern trick in:
> 
> getRows stmt >>=
>         mapM_ (\ (m :. n :. p :. Nil) ->
> 
> All in all I think it is a very good demonstration of what you can do 
> with heterogenous lists, and it's not really worse than HSQL when it 
> comes to type-safety.

Thanks.

> You might want to have a look at HaskellDB, 
> http://haskelldb.sourceforge.net/ . It uses a similar scheme for record 
> types. It adds a layer of type safety, and you construct the queries 
> using combinators.
> 
> You might want to be careful with collectRowsAsync. We have the same 
> thing in HaskellDB, and it turns out to be a problem with some databases 
> if you run a second query without getting all that data from the first 
> one. I think MySQL with the native drivers does it for example, but not 
> with ODBC.

About accessing record fields by name vs. position, that was one
reason I wanted to write this. I wasn't sure how to name fields with
expressions such as:

select min(a.s), avg(a.s), max(a.s), sum(a.s) from ...

and felt that it shouldn't be necessary either. Temporary names (X as
a, Y as b) are possible but cumbersome. Positional bindings seem more
lightweight and nimble and in tune with the rest of Haskell - they are
how function parameters are done, after all.

One thing that doesn't come out in the example is that it should also
be a lot easier to do assignments from singleton select statements as
above, with another utility function or two, which can be quite common
in database applications.

(min :. ave :. max :. sum :. Nil) <- doOneRow "select ..."

I've looked at HaskellDB, I was shying away from it because I thought
I needed a more direct mapping to SQL internals.

Thanks for the heads up on collectRowsAsync.

-- 
Frederik Eaton                         http://ofb.net/~frederik/

Re: [htoolkit-users] HSQL, HList

[Frederik E. <fre...@a5...>]

On Tue, Feb 22, 2005 at 09:51:35PM +0100, Shae Matijs Erisson wrote:
> Frederik Eaton <fre...@a5...> writes:
> 
> > Is there anyone on this list?
> 
> Me me! I'm here! I haven't gotten around to reading the HList paper though,
> so I won't be able to give you intelligent feedback on your code till I do.

Oh, don't read the whole paper, in fact you probably don't need to
read any of it, most of it goes far beyond what I use, which is pretty
self-explanatory.

 data a :* l = a :. l
 data HNil = Nil

e.g.

 -- x :: Bool :* String :* Int :* HNil
 x = True :. "Hi" :. 4 :. Nil

It's just a way of giving you something like a tuple type, but with
access to the internals so you can make instances based on the
structure. The important part of my module is:

 instance SqlRow HNil where
     getFieldValues s [] = return Nil
     getFieldValues s _ = fail "Wrong number of fields"

 instance (SqlBind a, SqlRow l) => SqlRow (a :* l) where
     getFieldValues s (f:fs) = do
         a <- getFieldValue s f 
         l <- getFieldValues s fs
         return (a :. l)

The paper does other neat things like defining classes for appending
two HList types and for accessing list elements by index (which has to
be encoded as a type-level natural).

-- 
Frederik Eaton                         http://ofb.net/~frederik/

Re: [htoolkit-users] HSQL, HList

[Bjorn B. <d00...@dt...>]

Frederik Eaton wrote:
> I wrote some functions which can be used with HSQL to make it a lot
> more concise, using the HList concept:
>=20
> http://ofb.net/~frederik/SqlRow/
>=20
> If anybody wants to look at it and give feedback. Maybe it could be
> incorporated into the library.

One difference to the current HSQL is that you access record fields by=20
position rather than by name. Not sure whether this is good or bad. One=20
problem is that there is as little type safety now as before, and it's=20
as easy to access a non-existing field.

The nice thing is that you can get back a whole row at a time, and I=20
like the pattern trick in:

getRows stmt >>=3D
         mapM_ (\ (m :. n :. p :. Nil) ->

All in all I think it is a very good demonstration of what you can do=20
with heterogenous lists, and it's not really worse than HSQL when it=20
comes to type-safety.

You might want to have a look at HaskellDB,=20
http://haskelldb.sourceforge.net/ . It uses a similar scheme for record=20
types. It adds a layer of type safety, and you construct the queries=20
using combinators.

You might want to be careful with collectRowsAsync. We have the same=20
thing in HaskellDB, and it turns out to be a problem with some databases=20
if you run a second query without getting all that data from the first=20
one. I think MySQL with the native drivers does it for example, but not=20
with ODBC.

> Is there anyone on this list?

Yes.

/Bj=F6rn

Re: [htoolkit-users] HSQL, HList

[Shae M. E. <sh...@Sc...>]

Frederik Eaton <fre...@a5...> writes:

> Is there anyone on this list?

Me me! I'm here! I haven't gotten around to reading the HList paper though,
so I won't be able to give you intelligent feedback on your code till I do.
-- 
Shae Matijs Erisson - http://www.ScannedInAvian.com/ - Sockmonster once said:
You could switch out the unicycles for badgers, and the game would be the same.

[htoolkit-users] HSQL, HList

[Frederik E. <fre...@a5...>]

I wrote some functions which can be used with HSQL to make it a lot
more concise, using the HList concept:

http://ofb.net/~frederik/SqlRow/

If anybody wants to look at it and give feedback. Maybe it could be
incorporated into the library.

Is there anyone on this list?

Frederik

[htoolkit-users] HSQL patch: collectRowsAsync

[Frederik E. <fre...@a5...>]

(needed a better subject)

On Tue, Feb 22, 2005 at 03:38:55AM -0800, Frederik Eaton wrote:
> Please apply:
> 
> --- HSQL/src/HSQL.hsc   2005-02-22 03:37:23.000000000 -0800
> +++ HSQL-modified/src/HSQL.hsc  2005-02-22 03:36:44.000000000 -0800
> @@ -606,3 +606,22 @@
>                                         return (x:xs)
>                                 else return []
>  
> +-- | The 'collectRowsASync' function is just like collectRows, but it
> +-- uses unsafeInterleaveIO to in the same manner as hGetContents to
> +-- cause rows to be read asynchronously from the database in an
> +-- "on-demand" fashion as list elements are accessed in the result.
> +collectRowsAsync :: (Statement -> IO a) -> Statement -> IO [a]
> +collectRowsAsync act stmt = loop
> +      where
> +        closeAndThrow e = do closeStatement stmt; throw e
> +        loop = unsafeInterleaveIO $ (do
> +         success <- catch (fetch stmt) closeAndThrow
> +         if success
> +            then do
> +              x <- catch (act stmt) closeAndThrow
> +              xs <- loop
> +              return (x:xs)
> +            else do
> +              closeStatement stmt
> +              return [])
> +
> 
> Thanks,
> 
>   Frederik
> 
> -- 
> Frederik Eaton                         http://ofb.net/~frederik/
> 

-- 
Frederik Eaton                         http://ofb.net/~frederik/