Example of a multi-row insert using libpq

libpq_multirow_insert.cc

#include <stdio.h>
#include <iostream>
using namespace std;

#include "opencv2/core/core.hpp"
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/nonfree/features2d.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/nonfree/nonfree.hpp"
using namespace cv;

#include <stdio.h>
#include <stdlib.h>
#include <libpq-fe.h>

static void exit_nicely(PGconn *conn)
{
    PQfinish(conn);
    exit(1);
}

int main( int argc, char** argv )
{
  // Parse Command Line Arguments
  if( argc != 3 ) { cout << argv[0] << " image.jpg pgid" << endl; return -1; }

  Mat img = imread( argv[1], CV_LOAD_IMAGE_GRAYSCALE );
  if( !img.data ) { cout << "[!] Error reading image " << endl; return -1; }

  long pgid = atol(argv[2]);

  // Run OpenCV Feature Detector
  BRISK detector;
  vector<KeyPoint> keypoints;
  Mat desc;
  Mat mask = Mat::ones(img.cols, img.rows, CV_8U);
  detector( img, mask, keypoints, desc, false );

  // Connect to Database
  const char *conninfo = "Connection URL to your Postgres Instance";
  PGconn *conn = PQconnectdb(conninfo);
  if (PQstatus(conn) != CONNECTION_OK) {
    fprintf(stderr, "Connection to database failed: %s", PQerrorMessage(conn));
    exit_nicely(conn);
  }

  int nElem = 6*keypoints.size();

  Oid* paramTypes = new Oid[nElem];
  char** paramValues = new char*[nElem];
  int* paramLengths = new int[nElem];
  int* paramFormats = new int[nElem];

  char* pgcmd = new char[256+64*keypoints.size()];
  strcpy(pgcmd,"INSERT INTO brisk VALUES ");

  // Insert features into database
  for(int i = 0; i < keypoints.size(); i++) {

    const double* feature = desc.ptr<double>(i);

    char* i0 = new char[64];
    char* i1;
    char* i2 = new char[64];
    char* i3 = new char[64];
    char* i4 = new char[64];
    char* i5 = new char[64];

    // convert everything to text for postgres, (except for the binary feature)
    snprintf(i0,2048,"%ld",pgid);
    i1 = (char*)feature;
    snprintf(i2,2048,"%f",keypoints[i].pt.x);
    snprintf(i3,2048,"%f",keypoints[i].pt.y);
    snprintf(i4,2048,"%f",keypoints[i].size);
    snprintf(i5,2048,"%f",keypoints[i].angle);

    paramTypes[6*i+0] = 0;  paramValues[6*i+0] = i0; paramFormats[6*i+0] = 0; paramLengths[6*i+0] = 0;
    paramTypes[6*i+1] = 17; paramValues[6*i+1] = i1; paramFormats[6*i+1] = 1; paramLengths[6*i+1] = desc.row(i).cols;
    paramTypes[6*i+2] = 0;  paramValues[6*i+2] = i2; paramFormats[6*i+2] = 0; paramLengths[6*i+2] = 0;
    paramTypes[6*i+3] = 0;  paramValues[6*i+3] = i3; paramFormats[6*i+3] = 0; paramLengths[6*i+3] = 0;
    paramTypes[6*i+4] = 0;  paramValues[6*i+4] = i4; paramFormats[6*i+4] = 0; paramLengths[6*i+4] = 0;
    paramTypes[6*i+5] = 0;  paramValues[6*i+5] = i5; paramFormats[6*i+5] = 0; paramLengths[6*i+5] = 0;

    char chunk[1024];
    snprintf(chunk,1024,"($%d,$%d,$%d,$%d,$%d,$%d)",6*i+1,6*i+2,6*i+3,6*i+4,6*i+5,6*i+6);

    if(i > 0) strcat(pgcmd,",");
    strcat(pgcmd,chunk);
  }

  // Insert data
  PGresult* res = PQexecParams(conn,
    pgcmd,
    nElem,
    paramTypes,
    paramValues,
    paramLengths,
    paramFormats,
    0
  );

  // Check for errors
  if ( PQresultStatus(res) != PGRES_COMMAND_OK ) {
    fprintf(stderr, "[!] Insert failed!\n%s", PQresultErrorMessage(res));
    PQclear(res);
    exit_nicely(conn);
  } else {
    printf("Insert succeeded.\n");
    PQclear(res);
  }

  PQfinish(conn);
  return 0;
}

http://adpgtech.blogspot.com/2014/09/importing-json-data.html

https://stackoverflow.com/questions/8250389/computed-calculated-columns-in-postgresql