added postgres backend

backends/postgres/src/postgres_error.cpp

@@ -0,0 +1,34 @@
+#include "postgres_error.hpp"
+
+#include <sstream>
+
+#include <libpq-fe.h>
+
+namespace matador::backends::postgres {
+
+void throw_postgres_error(const char *what, const std::string &source)
+{
+  std::stringstream msg;
+  msg << "postgres error (" << source << "): " << what;
+  throw std::logic_error(msg.str());
+}
+
+void throw_postgres_error(PGconn *db, const std::string &source)
+{
+  if (PQstatus(db) == CONNECTION_BAD) {
+    throw_postgres_error(PQerrorMessage(db), source);
+  }
+}
+
+void throw_postgres_error(PGresult *res, PGconn *db, const std::string &source, const std::string &sql)
+{
+  if (res == nullptr ||
+      (PQresultStatus(res) != PGRES_COMMAND_OK &&
+       PQresultStatus(res) != PGRES_TUPLES_OK)) {
+    std::stringstream msg;
+    msg << "postgres error (" << source << ", " << PQresultErrorField(res, PG_DIAG_SQLSTATE) << ") " << PQerrorMessage(db) << ": " << sql;
+    throw std::logic_error(msg.str());
+  }
+}
+
+}