add new example 'qsqlite': use SQL from Lisp, load QML images from DB

examples/qsqlite/cpp/qt.cpp

@@ -0,0 +1,94 @@
+#include "qt.h"
+#include <QSqlQuery>
+#include <QSqlError>
+#include <QQuickView>
+#include <QtDebug>
+
+QObject* ini() {
+  static QObject* qt = nullptr;
+  if (qt == nullptr) {
+    qt = new QT;
+  }
+  return qt;
+}
+
+QT::QT() : QObject() {
+}
+
+QVariant QT::dataPath(const QVariant& prefix) {
+  // for desktop
+  QString path = QStandardPaths::writableLocation(QStandardPaths::AppLocalDataLocation);
+  path.truncate(path.lastIndexOf(QChar('/')));
+  path.append(QStringLiteral("/lqml-qsqlite/") + prefix.toString());
+  return path;
+}
+
+// SQL
+
+QVariant QT::iniDb(const QVariant& vName, const QVariant& vQuickView) {
+  // add database image provider, in order to load images in QML directly from a SQL database
+  auto quickView = vQuickView.value<QQuickView*>();
+  quickView->engine()->addImageProvider(QLatin1String("db"), new DatabaseImageProvider(this));
+  // ini
+  db = QSqlDatabase::addDatabase("QSQLITE");
+  db.setDatabaseName(vName.toString());
+  return vName;
+}
+
+QVariant QT::sqlQuery(const QVariant& vQuery, const QVariant& vValues, const QVariant& vCols) {
+  QVariantList results;
+  QSqlQuery sqlQuery(db);
+  if (db.open()) {
+    QString query = vQuery.toString();
+    sqlQuery.prepare(vQuery.toString());
+    const QVariantList values = vValues.value<QVariantList>();
+    for (auto value : values) {
+      sqlQuery.addBindValue(value);
+    }
+    if (sqlQuery.exec()) {
+      auto cols = vCols.toInt();
+      while (sqlQuery.next()) {
+        if (cols > 1) {
+          QVariantList list;
+          for (auto r = 0; r < cols; r++) {
+            list << sqlQuery.value(r);
+          }
+          results << QVariant(list);
+        } else {
+          results << sqlQuery.value(0);
+        }
+      }
+      if (!cols && query.startsWith("insert", Qt::CaseInsensitive)) {
+        results << sqlQuery.lastInsertId();
+      }
+      db.close();
+      return results;
+    }
+    db.close();
+  }
+  QString text;
+  if (sqlQuery.lastError().isValid()) {
+    text = sqlQuery.lastError().text();
+  } else {
+    text = db.lastError().text();
+  }
+  qDebug() << "SQL error:" << text;
+  return QVariant();
+}
+
+// database image provider
+
+QPixmap DatabaseImageProvider::requestPixmap(const QString& name, QSize* size, const QSize& requestedSize) {
+  auto result = qt->sqlQuery(
+    "select data from images where name = ?",
+    QVariantList() << name,
+    1); // number of returned columns
+  QPixmap pixmap;
+  pixmap.loadFromData(result.value<QVariantList>().first().toByteArray());
+  *size = pixmap.size();
+  if (requestedSize.isValid() && (pixmap.size() != requestedSize)) {
+    pixmap = pixmap.scaled(requestedSize);
+  }
+  return pixmap;
+}
+