How to Store and Retrieve Image on SQLite: Difference between revisions

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'''English''' [[How_to_Store_and_Retrieve_an_Image_or_File_with_SQLite_Spanish|Español]] [[How_to_Store_and_Retrieve_Image_on_SQLite_Bulgarian|Български]]<br />[[Category:HowTo]]<br />[[Category:snippets]]
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= How to Store and Retrieve an Image or File with SQLite =
Images (or any other binary data, from files or otherwise) can be stored in a database.
One way to do it is converting the data into a QByteArray, and insert it into the database as a [[wikipedia:Binary large object|Binary Large OBject]] (BLOB).


Images or any files can be stored in a database. Here is one way to do it using the following steps:
Below is a full example of such a workflow, including reading the image back from the database and displaying it:


1. Read the system file into a QByteArray.<br />2. Store QByteArray as a Binary Large Object in database.
<source lang="cpp">
#include <QtSql>
#include <QtWidgets>


For example :
int main( int argc, char *argv[] )
{
    QApplication app( argc, argv );


<code><br /> QFile file&amp;amp;#40;fileName&amp;amp;#41;;<br /> if (!file.open(QIODevice::ReadOnly)) return;<br /> QByteArray byteArray = file.readAll();
    // Set up database
    QString dbName( "myDatabase.db3" );
    QFile::remove( dbName ); // delete sqlite file if it exists from a previous run
    QSqlDatabase db = QSqlDatabase::addDatabase( "QSQLITE" );
    db.setDatabaseName( dbName );
    db.open();
    QSqlQuery query = QSqlQuery( db );
    query.exec( "CREATE TABLE IF NOT EXISTS imgTable ( filename TEXT, imagedata BLOB )" );


QSqlQuery query;<br /> query.prepare(&quot;INSERT INTO imgtable (imgdata) VALUES (?)&quot;);<br /> query.addBindValue(byteArray);<br /> query.exec&amp;amp;#40;&amp;#41;;<br /></code>
    // Generate an image (in this case a screenshot) and store it in a QByteArray
    QScreen *screen = app.primaryScreen();
    QPixmap inPixmap = screen->grabWindow( 0 );
    QByteArray inByteArray;
    QBuffer inBuffer( &inByteArray );
    inBuffer.open( QIODevice::WriteOnly );
    inPixmap.save( &inBuffer, "PNG" ); // write inPixmap into inByteArray in PNG format


Now, the image/file can be retrieved like any other data<br /><code><br /> QSqlQuery query(&quot;SELECT imgdata FROM imgtable&amp;quot;);<br /> query.next();<br /> QByteArray array = query.value(0).toByteArray();<br /></code>
    // Alternatively, load an image file directly into a QByteArray
    // QFile file("screenshot.png");
    // if (!file.open(QIODevice::ReadOnly)) return;
    // QByteArray inByteArray = file.readAll();


Creating a QPixmap from QByteArray :<br /><code><br /> QPixmap pixmap = QPixmap();<br /> pixmap.loadFromData(array);<br /></code>
    // Insert image bytes into the database
    // Note: make sure to wrap the :placeholder in parenthesis
    query.prepare( "INSERT INTO imgTable (filename, imagedata) VALUES ('screenshot.png', :imageData)" );
    query.bindValue( ":imageData", inByteArray );
    if( !query.exec() )
        qDebug() << "Error inserting image into table:\n" << query.lastError();


It is done. Now the pixmap can be used in a Button as icon or in label etc.
    // Get image data back from database
    if( !query.exec( "SELECT imagedata from imgTable" ))
        qDebug() << "Error getting image from table:\n" << query.lastError();
    query.first();
    QByteArray outByteArray = query.value( 0 ).toByteArray();
    QPixmap outPixmap = QPixmap();
    outPixmap.loadFromData( outByteArray );
    db.close();
 
    // Display image
    QLabel myLabel;
    myLabel.setPixmap( outPixmap );
    myLabel.show();
 
    return app.exec();
}
</source>
 
[[Category:Snippets]]
[[Category:HowTo]]

Latest revision as of 14:00, 24 November 2015

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Images (or any other binary data, from files or otherwise) can be stored in a database. One way to do it is converting the data into a QByteArray, and insert it into the database as a Binary Large OBject (BLOB).

Below is a full example of such a workflow, including reading the image back from the database and displaying it:

#include <QtSql>
#include <QtWidgets>

int main( int argc, char *argv[] )
{
    QApplication app( argc, argv );

    // Set up database
    QString dbName( "myDatabase.db3" );
    QFile::remove( dbName ); // delete sqlite file if it exists from a previous run
    QSqlDatabase db = QSqlDatabase::addDatabase( "QSQLITE" );
    db.setDatabaseName( dbName );
    db.open();
    QSqlQuery query = QSqlQuery( db );
    query.exec( "CREATE TABLE IF NOT EXISTS imgTable ( filename TEXT, imagedata BLOB )" );

    // Generate an image (in this case a screenshot) and store it in a QByteArray
    QScreen *screen = app.primaryScreen();
    QPixmap inPixmap = screen->grabWindow( 0 );
    QByteArray inByteArray;
    QBuffer inBuffer( &inByteArray );
    inBuffer.open( QIODevice::WriteOnly );
    inPixmap.save( &inBuffer, "PNG" ); // write inPixmap into inByteArray in PNG format

    // Alternatively, load an image file directly into a QByteArray
    // QFile file("screenshot.png");
    // if (!file.open(QIODevice::ReadOnly)) return;
    // QByteArray inByteArray = file.readAll();

    // Insert image bytes into the database
    // Note: make sure to wrap the :placeholder in parenthesis
    query.prepare( "INSERT INTO imgTable (filename, imagedata) VALUES ('screenshot.png', :imageData)" );
    query.bindValue( ":imageData", inByteArray );
    if( !query.exec() )
        qDebug() << "Error inserting image into table:\n" << query.lastError();

    // Get image data back from database
    if( !query.exec( "SELECT imagedata from imgTable" ))
        qDebug() << "Error getting image from table:\n" << query.lastError();
    query.first();
    QByteArray outByteArray = query.value( 0 ).toByteArray();
    QPixmap outPixmap = QPixmap();
    outPixmap.loadFromData( outByteArray );
    db.close();

    // Display image
    QLabel myLabel;
    myLabel.setPixmap( outPixmap );
    myLabel.show();

    return app.exec();
}