/******************************************************************************
 * $Id: ogrpgdatasource.cpp,v 1.18 2003/05/21 03:59:42 warmerda Exp $
 *
 * Project:  OpenGIS Simple Features Reference Implementation
 * Purpose:  Implements OGRPGDataSource class.
 * Author:   Frank Warmerdam, warmerda@home.com
 *
 ******************************************************************************
 * Copyright (c) 2000, Frank Warmerdam
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 ******************************************************************************
 *
 * $Log: ogrpgdatasource.cpp,v $
 * Revision 1.18  2003/05/21 03:59:42  warmerda
 * expand tabs
 *
 * Revision 1.17  2002/12/12 14:28:35  warmerda
 * fixed bug in DeleteLayer
 *
 * Revision 1.16  2002/10/20 03:45:27  warmerda
 * added debug on table create command
 *
 * Revision 1.15  2002/10/09 18:30:10  warmerda
 * substantial upgrade to type handling, and preservations of width/precision
 *
 * Revision 1.14  2002/10/04 14:03:09  warmerda
 * added column name laundering support
 *
 * Revision 1.13  2002/05/09 16:48:08  warmerda
 * upgrade to quote table and field names
 *
 * Revision 1.12  2002/05/09 16:03:19  warmerda
 * major upgrade to support SRS better and add ExecuteSQL
 *
 * Revision 1.11  2002/03/01 20:42:00  warmerda
 * fixed parsing of connect string, see bug 107
 *
 * Revision 1.10  2002/01/13 21:48:32  warmerda
 * fixed addgeometrycolumn call to include pszDBname
 *
 * Revision 1.9  2002/01/13 16:23:16  warmerda
 * capture dbname= parameter for use in AddGeometryColumn() call
 *
 * Revision 1.8  2001/11/15 21:19:58  warmerda
 * added soft transaction semantics
 *
 * Revision 1.7  2001/09/28 04:03:52  warmerda
 * partially upraded to PostGIS 0.6
 *
 * Revision 1.6  2001/07/18 04:55:16  warmerda
 * added CPL_CSVID
 *
 * Revision 1.5  2001/06/26 20:59:13  warmerda
 * implement efficient spatial and attribute query support
 *
 * Revision 1.4  2001/06/20 16:10:24  warmerda
 * fixed PostGIS autodetect
 *
 * Revision 1.3  2001/06/19 22:29:12  warmerda
 * upgraded to include PostGIS support
 *
 * Revision 1.2  2000/11/23 06:03:35  warmerda
 * added Oid support
 *
 * Revision 1.1  2000/10/17 17:46:51  warmerda
 * New
 *
 */

#include "ogr_pg.h"
#include "cpl_conv.h"
#include "cpl_string.h"

CPL_CVSID("$Id: ogrpgdatasource.cpp,v 1.18 2003/05/21 03:59:42 warmerda Exp $");

static void OGRPGNoticeProcessor( void *arg, const char * pszMessage );

/************************************************************************/
/*                          OGRPGDataSource()                           */
/************************************************************************/

OGRPGDataSource::OGRPGDataSource()

{
    pszName = NULL;
    pszDBName = NULL;
    papoLayers = NULL;
    nLayers = 0;
    hPGConn = NULL;
    bHavePostGIS = FALSE;
    nSoftTransactionLevel = 0;

    nKnownSRID = 0;
    panSRID = NULL;
    papoSRS = NULL;
}

/************************************************************************/
/*                          ~OGRPGDataSource()                          */
/************************************************************************/

OGRPGDataSource::~OGRPGDataSource()

{
    int         i;

    FlushSoftTransaction();

    CPLFree( pszName );
    CPLFree( pszDBName );

    for( i = 0; i < nLayers; i++ )
        delete papoLayers[i];
    
    CPLFree( papoLayers );

    if( hPGConn != NULL )
        PQfinish( hPGConn );

    for( i = 0; i < nKnownSRID; i++ )
    {
        if( papoSRS[i] != NULL && papoSRS[i]->Dereference() == 0 )
            delete papoSRS[i];
    }
    CPLFree( panSRID );
    CPLFree( papoSRS );
}

/************************************************************************/
/*                                Open()                                */
/************************************************************************/

int OGRPGDataSource::Open( const char * pszNewName, int bUpdate,
                              int bTestOpen )

{
    CPLAssert( nLayers == 0 );

/* -------------------------------------------------------------------- */
/*      Verify postgresql prefix.                                       */
/* -------------------------------------------------------------------- */
    if( !EQUALN(pszNewName,"PG:",3) )
    {
        if( !bTestOpen )
            CPLError( CE_Failure, CPLE_AppDefined, 
                      "%s does not conform to PostgreSQL naming convention,"
                      " PG:*\n" );
        return FALSE;
    }
    
/* -------------------------------------------------------------------- */
/*      Try to establish connection.                                    */
/* -------------------------------------------------------------------- */
    hPGConn = PQconnectdb( pszNewName + 3 );
    if( hPGConn == NULL || PQstatus(hPGConn) == CONNECTION_BAD )
    {
        CPLError( CE_Failure, CPLE_AppDefined, 
                  "PGconnectcb failed.\n%s", 
                  PQerrorMessage(hPGConn) );
        PQfinish(hPGConn);
        hPGConn = NULL;
        return FALSE;
    }

    pszName = CPLStrdup( pszNewName );
    
    bDSUpdate = bUpdate;

/* -------------------------------------------------------------------- */
/*      Install a notice processor.                                     */
/* -------------------------------------------------------------------- */
    PQsetNoticeProcessor( hPGConn, OGRPGNoticeProcessor, this );

/* -------------------------------------------------------------------- */
/*      Try to establish the database name from the connection          */
/*      string passed.                                                  */
/* -------------------------------------------------------------------- */
    if( strstr(pszNewName, "dbname=") != NULL )
    {
        int     i;

        pszDBName = CPLStrdup( strstr(pszNewName, "dbname=") + 7 );

        for( i = 0; pszDBName[i] != '\0'; i++ )
        {
            if( pszDBName[i] == ' ' )                                   
            {
                pszDBName[i] = '\0';
                break;
            }
        }
    }
    else if( getenv( "USER" ) != NULL )
        pszDBName = CPLStrdup( getenv("USER") );
    else
        pszDBName = CPLStrdup( "unknown_dbname" );
        
    CPLDebug( "OGR_PG", "DBName=\"%s\"", pszDBName );

/* -------------------------------------------------------------------- */
/*      Test to see if this database instance has support for the       */
/*      PostGIS Geometry type.  If so, disable sequential scanning      */
/*      so we will get the value of the gist indexes.                   */
/* -------------------------------------------------------------------- */
    PGresult            *hResult;
    
    hResult = PQexec(hPGConn, "BEGIN");

    if( hResult && PQresultStatus(hResult) == PGRES_COMMAND_OK )
    {
        PQclear( hResult );

        hResult = PQexec(hPGConn, 
                         "SELECT oid FROM pg_type WHERE typname = 'geometry'" );
    }

    if( hResult && PQresultStatus(hResult) == PGRES_TUPLES_OK 
        && PQntuples(hResult) > 0 )
    {
        bHavePostGIS = TRUE;
        nGeometryOID = atoi(PQgetvalue(hResult,0,0));
    }
    else
        nGeometryOID = (Oid) 0;

    if( hResult )
        PQclear( hResult );

    hResult = PQexec(hPGConn, "SET ENABLE_SEQSCAN = OFF");
    PQclear( hResult );

    hResult = PQexec(hPGConn, "COMMIT");
    PQclear( hResult );

/* -------------------------------------------------------------------- */
/*      Get a list of available tables.                                 */
/* -------------------------------------------------------------------- */
    hResult = PQexec(hPGConn, "BEGIN");

    if( hResult && PQresultStatus(hResult) == PGRES_COMMAND_OK )
    {
        PQclear( hResult );

        hResult = PQexec(hPGConn, 
                         "DECLARE mycursor CURSOR for "
                         "SELECT relname FROM pg_class "
                         "WHERE relkind = 'r' AND relname !~ '^pg'" );
    }

    if( hResult && PQresultStatus(hResult) == PGRES_COMMAND_OK )
    {
        PQclear( hResult );
        hResult = PQexec(hPGConn, "FETCH ALL in mycursor" );
    }

    if( !hResult || PQresultStatus(hResult) != PGRES_TUPLES_OK )
    {
        CPLError( CE_Failure, CPLE_AppDefined, 
                  "%s", PQerrorMessage(hPGConn) );
        return FALSE;
    }

/* -------------------------------------------------------------------- */
/*      Parse the returned table list                                   */
/* -------------------------------------------------------------------- */
    char        **papszTableNames=NULL;
    int           iRecord;

    for( iRecord = 0; iRecord < PQntuples(hResult); iRecord++ )
    {
        const char *pszTable = PQgetvalue(hResult, iRecord, 0);

        if( EQUAL(pszTable,"spatial_ref_sys")
            || EQUAL(pszTable,"geometry_columns") )
            continue;

        papszTableNames = CSLAddString(papszTableNames, 
                                       PQgetvalue(hResult, iRecord, 0));
    }

/* -------------------------------------------------------------------- */
/*      Cleanup                                                         */
/* -------------------------------------------------------------------- */
    PQclear( hResult );

    hResult = PQexec(hPGConn, "CLOSE mycursor");
    PQclear( hResult );

    hResult = PQexec(hPGConn, "COMMIT");
    PQclear( hResult );

/* -------------------------------------------------------------------- */
/*      Get the schema of the available tables.                         */
/* -------------------------------------------------------------------- */
    for( iRecord = 0; 
         papszTableNames != NULL && papszTableNames[iRecord] != NULL;
         iRecord++ )
    {
        OpenTable( papszTableNames[iRecord], bUpdate, FALSE );
    }

    CSLDestroy( papszTableNames );
    
    return nLayers > 0 || bUpdate;
}

/************************************************************************/
/*                             OpenTable()                              */
/************************************************************************/

int OGRPGDataSource::OpenTable( const char *pszNewName, int bUpdate,
                                int bTestOpen )

{
/* -------------------------------------------------------------------- */
/*      Create the layer object.                                        */
/* -------------------------------------------------------------------- */
    OGRPGLayer  *poLayer;

    poLayer = new OGRPGTableLayer( this, pszNewName, bUpdate );

/* -------------------------------------------------------------------- */
/*      Add layer to data source layer list.                            */
/* -------------------------------------------------------------------- */
    papoLayers = (OGRPGLayer **)
        CPLRealloc( papoLayers,  sizeof(OGRPGLayer *) * (nLayers+1) );
    papoLayers[nLayers++] = poLayer;
    
    return TRUE;
}

/************************************************************************/
/*                            DeleteLayer()                             */
/************************************************************************/

void OGRPGDataSource::DeleteLayer( const char *pszLayerName )

{
    int iLayer;

/* -------------------------------------------------------------------- */
/*      Try to find layer.                                              */
/* -------------------------------------------------------------------- */
    for( iLayer = 0; iLayer < nLayers; iLayer++ )
    {
        if( EQUAL(pszLayerName,papoLayers[iLayer]->GetLayerDefn()->GetName()) )
            break;
    }

    if( iLayer == nLayers )
        return;

/* -------------------------------------------------------------------- */
/*      Blow away our OGR structures related to the layer.  This is     */
/*      pretty dangerous if anything has a reference to this layer!     */
/* -------------------------------------------------------------------- */
    CPLDebug( "OGR_PG", "DeleteLayer(%s)", pszLayerName );

    delete papoLayers[iLayer];
    memmove( papoLayers + iLayer, papoLayers + iLayer + 1, 
             sizeof(void *) * (nLayers - iLayer - 1) );
    nLayers--;

/* -------------------------------------------------------------------- */
/*      Remove from the database.                                       */
/* -------------------------------------------------------------------- */
    PGresult            *hResult;
    char                szCommand[1024];

    hResult = PQexec(hPGConn, "BEGIN");
    PQclear( hResult );

    if( bHavePostGIS )
    {
        sprintf( szCommand, 
                 "SELECT DropGeometryColumn('%s','%s','wkb_geometry')",
                 pszDBName, pszLayerName );

        hResult = PQexec( hPGConn, szCommand );
        PQclear( hResult );
    }

    sprintf( szCommand, "DROP TABLE %s", pszLayerName );
    hResult = PQexec( hPGConn, szCommand );
    PQclear( hResult );
    
    sprintf( szCommand, "DROP SEQUENCE %s_ogc_fid_seq", pszLayerName );
    hResult = PQexec( hPGConn, szCommand );
    PQclear( hResult );
    
    hResult = PQexec(hPGConn, "COMMIT");
    PQclear( hResult );
}

/************************************************************************/
/*                            CreateLayer()                             */
/************************************************************************/

OGRLayer *
OGRPGDataSource::CreateLayer( const char * pszLayerName,
                              OGRSpatialReference *poSRS,
                              OGRwkbGeometryType eType,
                              char ** papszOptions )

{
    PGresult            *hResult;
    char                szCommand[1024];
    const char          *pszGeomType;

/* -------------------------------------------------------------------- */
/*      Do we already have this layer?  If so, should we blow it        */
/*      away?                                                           */
/* -------------------------------------------------------------------- */
    int iLayer;

    for( iLayer = 0; iLayer < nLayers; iLayer++ )
    {
        if( EQUAL(pszLayerName,papoLayers[iLayer]->GetLayerDefn()->GetName()) )
        {
            if( CSLFetchNameValue( papszOptions, "OVERWRITE" ) != NULL
                && !EQUAL(CSLFetchNameValue(papszOptions,"OVERWRITE"),"NO") )
            {
                DeleteLayer( pszLayerName );
            }
            else
            {
                CPLError( CE_Failure, CPLE_AppDefined, 
                          "Layer %s already exists, CreateLayer failed.\n"
                          "Use the layer creation option OVERWRITE=YES to "
                          "replace it.",
                          pszLayerName );
                return NULL;
            }
        }
    }

/* -------------------------------------------------------------------- */
/*      Handle the GEOM_TYPE option.                                    */
/* -------------------------------------------------------------------- */
    pszGeomType = CSLFetchNameValue( papszOptions, "GEOM_TYPE" );
    if( pszGeomType == NULL )
    {
        if( bHavePostGIS )
            pszGeomType = "geometry";
        else
            pszGeomType = "bytea";
    }

    if( bHavePostGIS && !EQUAL(pszGeomType,"geometry") )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "Can't override GEOM_TYPE in PostGIS enabled databases.\n"
                  "Creation of layer %s with GEOM_TYPE %s has failed.",
                  pszLayerName, pszGeomType );
        return NULL;
    }

/* -------------------------------------------------------------------- */
/*      Try to get the SRS Id of this spatial reference system,         */
/*      adding tot the srs table if needed.                             */
/* -------------------------------------------------------------------- */
    int nSRSId = -1;

    if( poSRS != NULL )
        nSRSId = FetchSRSId( poSRS );

/* -------------------------------------------------------------------- */
/*      Create a basic table with the FID.  Also include the            */
/*      geometry if this is not a PostGIS enabled table.                */
/* -------------------------------------------------------------------- */
    hResult = PQexec(hPGConn, "BEGIN");
    PQclear( hResult );

    if( !bHavePostGIS )
        sprintf( szCommand, 
                 "CREATE TABLE \"%s\" ( "
                 "   OGC_FID SERIAL, "
                 "   WKB_GEOMETRY %s )",
                 pszLayerName, pszGeomType );
    else
        sprintf( szCommand, 
                 "CREATE TABLE \"%s\" ( OGC_FID SERIAL )", 
                 pszLayerName );

    CPLDebug( "OGR_PG", "PQexec(%s)", szCommand );
    hResult = PQexec(hPGConn, szCommand);
    if( PQresultStatus(hResult) != PGRES_COMMAND_OK )
    {
        CPLError( CE_Failure, CPLE_AppDefined, 
                  "%s\n%s", szCommand, PQerrorMessage(hPGConn) );

        PQclear( hResult );
        hResult = PQexec( hPGConn, "ROLLBACK" );
        PQclear( hResult );

        return NULL;
    }
    
    PQclear( hResult );

/* -------------------------------------------------------------------- */
/*      Eventually we should be adding this table to a table of         */
/*      "geometric layers", capturing the WKT projection, and           */
/*      perhaps some other housekeeping.                                */
/* -------------------------------------------------------------------- */
    if( bHavePostGIS )
    {
        const char *pszGeometryType;

        switch( wkbFlatten(eType) )
        {
          case wkbPoint:
            pszGeometryType = "POINT";
            break;

          case wkbLineString:
            pszGeometryType = "LINESTRING";
            break;

          case wkbPolygon:
            pszGeometryType = "POLYGON";
            break;

          case wkbMultiPoint:
            pszGeometryType = "MULTIPOINT";
            break;

          case wkbMultiLineString:
            pszGeometryType = "MULTILINESTRING";
            break;

          case wkbMultiPolygon:
            pszGeometryType = "MULTIPOLYGON";
            break;

          case wkbGeometryCollection:
            pszGeometryType = "GEOMETRYCOLLECTION";
            break;

          default:
            pszGeometryType = "GEOMETRY";
            break;

        }

        sprintf( szCommand, 
                 "SELECT AddGeometryColumn('%s','%s','wkb_geometry',%d,'%s',%d)",
                 pszDBName, pszLayerName, nSRSId, pszGeometryType, 3 );

        CPLDebug( "OGR_PG", "PQexec(%s)", szCommand );
        hResult = PQexec(hPGConn, szCommand);

        if( !hResult 
            || PQresultStatus(hResult) != PGRES_TUPLES_OK )
        {
            CPLError( CE_Failure, CPLE_AppDefined, 
                      "AddGeometryColumn failed for layer %s, layer creation has failed.",
                      pszLayerName );
            
            PQclear( hResult );

            hResult = PQexec(hPGConn, "ROLLBACK");
            PQclear( hResult );

            return NULL;
        }
    }

/* -------------------------------------------------------------------- */
/*      Complete, and commit the transaction.                           */
/* -------------------------------------------------------------------- */
    hResult = PQexec(hPGConn, "COMMIT");
    PQclear( hResult );

/* -------------------------------------------------------------------- */
/*      Create the layer object.                                        */
/* -------------------------------------------------------------------- */
    OGRPGTableLayer     *poLayer;

    poLayer = new OGRPGTableLayer( this, pszLayerName, TRUE, nSRSId );

    poLayer->SetLaunderFlag( CSLFetchBoolean(papszOptions,"LAUNDER",FALSE) );
    poLayer->SetPrecisionFlag( CSLFetchBoolean(papszOptions,"PRECISION",TRUE));

/* -------------------------------------------------------------------- */
/*      Add layer to data source layer list.                            */
/* -------------------------------------------------------------------- */
    papoLayers = (OGRPGLayer **)
        CPLRealloc( papoLayers,  sizeof(OGRPGLayer *) * (nLayers+1) );
    
    papoLayers[nLayers++] = poLayer;

    return poLayer;
}

/************************************************************************/
/*                           TestCapability()                           */
/************************************************************************/

int OGRPGDataSource::TestCapability( const char * pszCap )

{
    if( EQUAL(pszCap,ODsCCreateLayer) )
        return TRUE;
    else
        return FALSE;
}

/************************************************************************/
/*                              GetLayer()                              */
/************************************************************************/

OGRLayer *OGRPGDataSource::GetLayer( int iLayer )

{
    if( iLayer < 0 || iLayer >= nLayers )
        return NULL;
    else
        return papoLayers[iLayer];
}

/************************************************************************/
/*                        OGRPGNoticeProcessor()                        */
/************************************************************************/

static void OGRPGNoticeProcessor( void *arg, const char * pszMessage )

{
    CPLDebug( "OGR_PG_NOTICE", "%s", pszMessage );
}

/************************************************************************/
/*                      InitializeMetadataTables()                      */
/*                                                                      */
/*      Create the metadata tables (SPATIAL_REF_SYS and                 */
/*      GEOMETRY_COLUMNS).                                              */
/************************************************************************/

OGRErr OGRPGDataSource::InitializeMetadataTables()

{
    // implement later.
    return OGRERR_FAILURE;
}

/************************************************************************/
/*                              FetchSRS()                              */
/*                                                                      */
/*      Return a SRS corresponding to a particular id.  Note that       */
/*      reference counting should be honoured on the returned           */
/*      OGRSpatialReference, as handles may be cached.                  */
/************************************************************************/

OGRSpatialReference *OGRPGDataSource::FetchSRS( int nId )

{
    if( nId < 0 )
        return NULL;

/* -------------------------------------------------------------------- */
/*      First, we look through our SRID cache, is it there?             */
/* -------------------------------------------------------------------- */
    int  i;

    for( i = 0; i < nKnownSRID; i++ )
    {
        if( panSRID[i] == nId )
            return papoSRS[i];
    }

/* -------------------------------------------------------------------- */
/*      Try looking up in spatial_ref_sys table.                        */
/* -------------------------------------------------------------------- */
    PGresult        *hResult;
    char            szCommand[1024];
    OGRSpatialReference *poSRS;
        
    SoftStartTransaction();

    sprintf( szCommand, 
             "SELECT srtext FROM spatial_ref_sys "
             "WHERE srid = %d", 
             nId );
    hResult = PQexec(hPGConn, szCommand );

    if( hResult 
        && PQresultStatus(hResult) == PGRES_TUPLES_OK 
        && PQntuples(hResult) == 1 )
    {
        char *pszWKT;

        pszWKT = PQgetvalue(hResult,0,0);
        poSRS = new OGRSpatialReference();
        if( poSRS->importFromWkt( &pszWKT ) != OGRERR_NONE )
        {
            delete poSRS;
            poSRS = NULL;
        }
    }

    PQclear( hResult );
    SoftCommit();

/* -------------------------------------------------------------------- */
/*      Add to the cache.                                               */
/* -------------------------------------------------------------------- */
    panSRID = (int *) CPLRealloc(panSRID,sizeof(int) * (nKnownSRID+1) );
    papoSRS = (OGRSpatialReference **) 
        CPLRealloc(papoSRS, sizeof(void*) * (nKnownSRID + 1) );
    panSRID[nKnownSRID] = nId;
    papoSRS[nKnownSRID] = poSRS;

    return poSRS;
}

/************************************************************************/
/*                             FetchSRSId()                             */
/*                                                                      */
/*      Fetch the id corresponding to an SRS, and if not found, add     */
/*      it to the table.                                                */
/************************************************************************/

int OGRPGDataSource::FetchSRSId( OGRSpatialReference * poSRS )

{
    PGresult            *hResult;
    char                szCommand[10000];
    char                *pszWKT = NULL;
    int                 nSRSId;

    if( poSRS == NULL )
        return -1;

/* -------------------------------------------------------------------- */
/*      Translate SRS to WKT.                                           */
/* -------------------------------------------------------------------- */
    if( poSRS->exportToWkt( &pszWKT ) != OGRERR_NONE )
        return -1;
    
    CPLAssert( strlen(pszWKT) < sizeof(szCommand) - 500 );

/* -------------------------------------------------------------------- */
/*      Try to find in the existing table.                              */
/* -------------------------------------------------------------------- */
    hResult = PQexec(hPGConn, "BEGIN");

    sprintf( szCommand, 
             "SELECT srid FROM spatial_ref_sys WHERE srtext = '%s'",
             pszWKT );
    hResult = PQexec(hPGConn, szCommand );
                     
/* -------------------------------------------------------------------- */
/*      We got it!  Return it.                                          */
/* -------------------------------------------------------------------- */
    if( hResult && PQresultStatus(hResult) == PGRES_TUPLES_OK 
        && PQntuples(hResult) > 0 )
    {
        nSRSId = atoi(PQgetvalue( hResult, 0, 0 ));
        
        PQclear( hResult );

        hResult = PQexec(hPGConn, "COMMIT");
        PQclear( hResult );

        return nSRSId;
    }
    
/* -------------------------------------------------------------------- */
/*      If the command actually failed, then the metadata table is      */
/*      likely missing. Try defining it.                                */
/* -------------------------------------------------------------------- */
    int         bTableMissing;

    bTableMissing = 
        hResult == NULL || PQresultStatus(hResult) == PGRES_NONFATAL_ERROR;

    hResult = PQexec(hPGConn, "COMMIT");
    PQclear( hResult );

    if( bTableMissing )
    {
        if( InitializeMetadataTables() != OGRERR_NONE )
            return -1;
    }

/* -------------------------------------------------------------------- */
/*      Get the current maximum srid in the srs table.                  */
/* -------------------------------------------------------------------- */
    hResult = PQexec(hPGConn, "BEGIN");
    PQclear( hResult );

    hResult = PQexec(hPGConn, "SELECT MAX(srid) FROM spatial_ref_sys" );

    if( hResult && PQresultStatus(hResult) == PGRES_TUPLES_OK )
    {
        nSRSId = atoi(PQgetvalue(hResult,0,0)) + 1;
        PQclear( hResult );
    }
    else
        nSRSId = 1;
    
/* -------------------------------------------------------------------- */
/*      Try adding the SRS to the SRS table.                            */
/* -------------------------------------------------------------------- */
    sprintf( szCommand, 
             "INSERT INTO spatial_ref_sys (srid,srtext) VALUES (%d,'%s')",
             nSRSId, pszWKT );
             
    hResult = PQexec(hPGConn, szCommand );
    PQclear( hResult );

    hResult = PQexec(hPGConn, "COMMIT");
    PQclear( hResult );

    return nSRSId;
}

/************************************************************************/
/*                        SoftStartTransaction()                        */
/*                                                                      */
/*      Create a transaction scope.  If we already have a               */
/*      transaction active this isn't a real transaction, but just      */
/*      an increment to the scope count.                                */
/************************************************************************/

OGRErr OGRPGDataSource::SoftStartTransaction()

{
    nSoftTransactionLevel++;

    if( nSoftTransactionLevel == 1 )
    {
        PGresult            *hResult;
        PGconn          *hPGConn = GetPGConn();

        hResult = PQexec(hPGConn, "BEGIN");

        if( !hResult || PQresultStatus(hResult) != PGRES_COMMAND_OK )
            return OGRERR_FAILURE;

        PQclear( hResult );
    }

    return OGRERR_NONE;
}

/************************************************************************/
/*                             SoftCommit()                             */
/*                                                                      */
/*      Commit the current transaction if we are at the outer           */
/*      scope.                                                          */
/************************************************************************/

OGRErr OGRPGDataSource::SoftCommit()

{
    if( nSoftTransactionLevel <= 0 )
    {
        CPLDebug( "OGR_PG", "SoftCommit() with no transaction active." );
        return OGRERR_FAILURE;
    }

    nSoftTransactionLevel--;

    if( nSoftTransactionLevel == 0 )
    {
        PGresult            *hResult;
        PGconn          *hPGConn = GetPGConn();

        hResult = PQexec(hPGConn, "COMMIT");

        if( !hResult || PQresultStatus(hResult) != PGRES_COMMAND_OK )
            return OGRERR_FAILURE;

        PQclear( hResult );
    }

    return OGRERR_NONE;
}

/************************************************************************/
/*                            SoftRollback()                            */
/*                                                                      */
/*      Force a rollback of the current transaction if there is one,    */
/*      even if we are nested several levels deep.                      */
/************************************************************************/

OGRErr OGRPGDataSource::SoftRollback()

{
    if( nSoftTransactionLevel <= 0 )
    {
        CPLDebug( "OGR_PG", "SoftRollback() with no transaction active." );
        return OGRERR_FAILURE;
    }

    nSoftTransactionLevel = 0;

    PGresult            *hResult;
    PGconn              *hPGConn = GetPGConn();
    
    hResult = PQexec(hPGConn, "ROLLBACK");
    
    if( !hResult || PQresultStatus(hResult) != PGRES_COMMAND_OK )
        return OGRERR_FAILURE;
    
    PQclear( hResult );

    return OGRERR_NONE;
}

/************************************************************************/
/*                        FlushSoftTransaction()                        */
/*                                                                      */
/*      Force the unwinding of any active transaction, and it's         */
/*      commit.                                                         */
/************************************************************************/

OGRErr OGRPGDataSource::FlushSoftTransaction()

{
    if( nSoftTransactionLevel <= 0 )
        return OGRERR_NONE;

    nSoftTransactionLevel = 1;

    return SoftCommit();
}

/************************************************************************/
/*                             ExecuteSQL()                             */
/************************************************************************/

OGRLayer * OGRPGDataSource::ExecuteSQL( const char *pszSQLCommand,
                                        OGRGeometry *poSpatialFilter,
                                        const char *pszDialect )

{
    if( poSpatialFilter != NULL )
    {
        CPLDebug( "OGR_PG", 
          "Spatial filter ignored for now in OGRPGDataSource::ExecuteSQL()" );
    }

/* -------------------------------------------------------------------- */
/*      Execute the statement.                                          */
/* -------------------------------------------------------------------- */
    PGresult            *hResult;
    
    hResult = PQexec(hPGConn, "BEGIN");

    if( hResult && PQresultStatus(hResult) == PGRES_COMMAND_OK )
    {
        PQclear( hResult );

        hResult = PQexec(hPGConn, pszSQLCommand );
    }

/* -------------------------------------------------------------------- */
/*      Do we have a tuple result? If so, instantiate a results         */
/*      layer for it.                                                   */
/* -------------------------------------------------------------------- */

    if( hResult && PQresultStatus(hResult) == PGRES_TUPLES_OK 
        && PQntuples(hResult) > 0 )
    {
        OGRPGResultLayer *poLayer = NULL;

        poLayer = new OGRPGResultLayer( this, pszSQLCommand, hResult );
        
        return poLayer;
    }

/* -------------------------------------------------------------------- */
/*      Generate an error report if an error occured.                   */
/* -------------------------------------------------------------------- */
    if( hResult && 
        (PQresultStatus(hResult) == PGRES_NONFATAL_ERROR
         || PQresultStatus(hResult) == PGRES_FATAL_ERROR ) )
    {
        CPLError( CE_Failure, CPLE_AppDefined, 
                  "%s", PQresultErrorMessage( hResult ) );
    }

    if( hResult )
        PQclear( hResult );

    hResult = PQexec(hPGConn, "COMMIT");
    PQclear( hResult );

    return NULL;
}

/************************************************************************/
/*                          ReleaseResultSet()                          */
/************************************************************************/

void OGRPGDataSource::ReleaseResultSet( OGRLayer * poLayer )

{
    delete poLayer;
}
