talking to postgresql from C/C++ - Mailing list pgsql-hackers

I've been trying to get information on a programming interface to the database.  Over the last while Dave Page and I
haveemailed each other.  Dave has suggested I join the hacker maillist. 

Thus I am forwarding the communication I sent to Dave.  I hope this is approriated in this channel.  If not please
advisewhere I should go. 


I'll look forward to some clarification about what is or is not available by way of talking to the database from
languageslike C. 

Thanks.

Terrell Larson


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Date: Fri, 7 Mar 2003 04:18:45 -0700
From: terr
To: Dave Page <dpage@vale-housing.co.uk>
Subject: Re: Fwd: ODBC docs
Message-ID: <20030307041844.I24536@saturn.terralogic.net>
References: <03AF4E498C591348A42FC93DEA9661B8259D29@mail.vale-housing.co.uk>
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In-Reply-To: <03AF4E498C591348A42FC93DEA9661B8259D29@mail.vale-housing.co.uk>; from dpage@vale-housing.co.uk on Fri,
Mar07, 2003 at 08:49:00AM -0000 


Over at M$, I see the following:

    * SQQLAllocConnect Function
    * SQLAllocEnv Function
    * SQLAllocHandle Function
    * SQLAllocStmt Function
    * SQLBindCol Function
    * SQLBindParameter Function
    * SQLBrowseConnect Function
    * SQLBulkOperations Function
    * SQLCancel Function
    * SQLCloseCursor Function
    * SQLColAttribute Function
    * SQLColAttributes Function
    * SQLColumnPrivileges Function
    * SQLColumns Function
    * SQLConnect Function
    * SQLCopyDesc Function
    * SQLDataSources Function
    * SQLDescribeCol Function
    * SQLDescribeParam Function
    * SQLDisconnect Function
    * SQLDriverConnect Function
    * SQLDrivers Function
    * SQLEndTran Function
    * SQLError Function
    * SQLExecDirect Function
    * SQLExecute Function
    * SQLExtendedFetch Function
    * SQLFetch Function
    * SQLFetchScroll Function
    * SQLForeignKeys Function
    * SQLFreeConnect Function
    * SQLFreeEnv Function
    * SQLFreeHandle Function
    * SQLFreeStmt Function
    * SQLGetConnectAttr Function
    * SQLGetConnectOption Function
    * SQLGetCursorName Function
    * SQLGetData Function
    * SQLGetDescField Function
    * SQLGetDescRec Function
    * SQLGetDiagField Function
    * SQLGetDiagRec Function
    * SQLGetEnvAttr Function
    * SQLGetFunctions Function
    * SQLGetInfo Function
    * SQLGetStmtAttr Function
    * SQLGetStmtOption Function
    * SQLGetTypeInfo Function
    * SQLMoreResults Function
    * SQLNativeSql Function
    * SQLNumParams Function
    * SQLNumResultCols Function
    * SQLParamData Function
    * SQLParamOptions Function
    * SQLPrepare Function
    * SQLPrimaryKeys Function
    * SQLProcedureColumns Function
    * SQLProcedures Function
    * SQLPutData Function
    * SQLRowCount Function
    * SQLSetConnectAttr Function
    * SQLSetConnectOption Function
    * SQLSetCursorName Function
    * SQLSetDescField Function
    * SQLSetDescRec Function
    * SQLSetEnvAttr Function
    * SQLSetParam Function
    * SQLSetPos Function
    * SQLSetScrollOptions Function
    * SQLSetStmtAttr Function
    * SQLSetStmtOption Function
    * SQLSpecialColumns Function
    * SQLStatistics Function
    * SQLTablePrivileges Function
    * SQLTables Function
    * SQLTransact Function


This looks like the API.  Thanks.  Now - IMHO "we" should have these docs on "our" website instead of having to rely on
M$.  

It this is truely not currently available I may be able to start flanging something up.  I suspect that there may be
bitsand peices around... perhaps the whole thing. 

Also - I really want to find out how some of these functions are implemented.  The problem I'm looking at is that:

(1) if I use ecpg then I get over 1000 parameters stuffed into some of the calls.  This is just plain NUTZ.  Aside from
itbeing virtually insane to try to pass this many parameters to a function call, it makes absolutly no sense to stack
over1000 addresses, call the interface, find out the row is not present, tear down the addresses, build the row (about
100fields), stack over 1000 addresses bak up, call the interface to post the row, and tear the stack back down only to
dothis all over again for the next row. 

Passing this many addresses is so NUTZ that when I popped into the #C developers group on Freenode and also the #debian
channelsand asked if anyone knew the maximum number of parameters one could pass into a function call - that they
startedto abuse me!  haha.  Some must have thought I was a 1st year uni student without much common sense.  What can I
say. IMHO 1000+ parameters is an embarrasment. 

(2) if I use libpg then I apparently have to map each and every column for each row over and over, column by column for
eachrow in a manner that is very similar to (1).  None of the columns change between calls to the database and none of
thevariables move around. (in this case the buffers are statically mapped - by design)  I should be able to build up a
tableof the mapping of MY C VARIABLES into the columns in the table ONCE at the beginning of a run and then use it over
andover row by row as I post things into the database. 

(3) The update functions I have encountered so far are basically a SQL INSERT statement.  This means that my code must
gothrough the buffer containing the row to be inserted and build up a HUGE string with ugly codes in it - converting
binaryvalues into ACSII and eventually having done this HUGE amount of work, pass the string to the interface so that
itcan parse the string which is a HUGE amount of work and eventually get the data back into a mapped binary buffer from
whichthe database manager can arrange to store it in the database on disk. 

To put it bluntly this sort of interface is INSANE.

What I need is the following structure passed into the database manager:

struct record_mapping {
  void *address_of_field;  // a pointer to the data
  enum field_type;         // as defined: pgint, pgfloat, pgvarchar, pgblob...
  char *field_name;        // internal name in the database
  etc
  etc
  etc
}

and then I can call an initialization routine passing either this structure or the information in it to the database
managerin say a cursor.   

If this interface does NOT exist then it should be created.

If I were to do this then I would create the following functions:

pg_cursor_address = pg_Create_Cursor ( db_handle, max_number_variables );

if the address is NULL then the function failed.  the error code should be in db_handle.  If we can't put it into the
handle,then we pass &success, an int. 

int success = pg_Define_Column_Entry ( pg_cursor_address, &myvar, pg_field_type, "column-name", .... );

If it is successful, sucess = 0, if fails, sucess has the error code.

pg_cursor_address = pg_Destroy_Cursor ( pg_cursor_address );

This routine returns a NULL thus detroying the pointer.  Meanwhile any malloc()'s are freed and the cursor is torn
down.

success = pg_Exec_Query ( pg_cursor_address, "insert");

an example of how to insert a row.  success = 0 => ok.  non-zero carries an extensive list of reasons.  The text of the
reasonshould be retrivable with a sister function. 

success = pg_Exec_Query ( pg_cursor_address, "select where blah" );

an example of how to fetch a row.  Only the first selected row is copied into the transfer buffer.  Again success = 0
impliesyou got the data. 

success = pg_Exec_Query ( pg_cursor_address, "next-row" );

When the last row has been returned, a success is set to a non-zero.

success = pg_Exec_Query ( pg_cursor_address, "replace-row" );

In this case, the application fetched the row, updated it and wants the replacement posted into the database.

------------

I'll stop now.  I just fired this off the top of my head.  I'm looking to find an interface that will sort of work like
this,and work relatively efficiently.  Perhaps this is the ODBC interface and perhaps it is the libpg interface... but
ifthis is in libpg I sure could not find it. 

IF this interface does NOT exist then I could perhaps write it.  Now, I am not familiar with the source tree or what
internalfunctions and structures might be available to support this.  Clearly I could write an interface like this and
hookit up to libpg - but the libpg from what I can tell does NOT support a cursor and needs to build up a call column
bycolumn and this is what we're trying to avoid. 

Given the excellent quality of PostgreSQL I just *HAVE* to believe a suitable interface already exists and I have just
notbeen able to find it. 

Again, if it does not exist, with a very small amount of guidence I figure I can probably make it happen.  If this is
thedirection we need to go, then I would like the opportunity to knock heads with some people who are already familiar
withwhat is out there so as to define exactly HOW this interface should look so that it comes out looking clean and
wellthought out and not some botch created by an amature. 

Thanks for your help.






On Fri, Mar 07, 2003 at 08:49:00AM -0000, Dave Page wrote:
> Why not take a look at msdn.microsoft.com? There is some very useful
> documentation in the Data Access SDK on ODBC - and after all, Microsoft
> did invent it!
>
> Regards, Dave.
>
> > -----Original Message-----
> > From: terr@terralogic.net [mailto:terr@terralogic.net]
> > Sent: 07 March 2003 09:43
> > To: Dave Page
> > Subject: Re: Fwd: ODBC docs
> >
> >
> > I've been through that documentation.  THere is some docs on
> > using the odbc interfce from JODBC and from Python, but there
> > is nothing on how to use it from C or C++.
> >
> > In my case, I was planning on doing the database interface in
> > C, bit C++
> >
> >
> > On Fri, Mar 07, 2003 at 08:03:23AM -0000, Dave Page wrote:
> > > Should be OK now. The server had a RAID controller failure.
> > >
> > > Regards, Dave.
> > >
> > > > -----Original Message-----
> > > > From: terr@terralogic.net [mailto:terr@terralogic.net]
> > > > Sent: 07 March 2003 00:45
> > > > To: Dave Page
> > > > Subject: Re: Fwd: ODBC docs
> > > >
> > > >
> > > > This link takes me to here:
> > > > http://gborg.postgresql.org/project/psqlodbc/projdisplay.php
> > > >
> > > > there is a link there which says "PostgreSQL Docs"  the link
> > > > does not work and I get this:
> > > >
> > > > Warning: pg_exec(): supplied argument is not a valid
> > > > PostgreSQL link resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 184
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 187
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 190
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 191
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 192
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 193
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 194
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 195
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 196
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 197
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 198
> > > >
> > > > Warning: pg_result(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/globals.php on line 205
> > > >
> > > > Warning: pg_exec(): supplied argument is not a valid
> > > > PostgreSQL link resource in
> > > > /usr/local/www/www.postgresql.org/docs/view.php on line 23
> > > >
> > > > Warning: pg_numrows(): supplied argument is not a valid
> > > > PostgreSQL result resource in
> > > > /usr/local/www/www.postgresql.org/docs/view.php on line 25
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > On Fri, Mar 07, 2003 at 12:19:23AM -0000, Dave Page wrote:
> > > > > It's rumoured that Bruce Momjian once said:
> > > > > >
> > > > > > You can find stuff at odbc.postgresql.org, I think.
> > > > > >
> > > > > >
> > > > >
> > > > > Hi Bruce,
> > > > >
> > > > > That's now deprecated. It's all at
> > > > > http://gborg.postgresql.org/project/psqlodbc/ now.
> > Regards, Dave.
> > > > >
> > > > >
> > > >
> >

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