Difference between revisions of "How to Store and Retrieve Image on SQLite"

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{{LangSwitch}}
  
[[Category:snippets]]
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Images (or any other binary data, from files or otherwise) can be stored in a database.
[[Category:HowTo]]
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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).
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Below is a full example of such a workflow, including reading the image back from the database and displaying it:
  
'''English''' | [[How_to_Store_and_Retrieve_Image_on_SQLite_German|Deutsch]] | [[How_to_Store_and_Retrieve_an_Image_or_File_with_SQLite_Spanish|Español]] | [[How_to_Store_and_Retrieve_Image_on_SQLite_Bulgarian|Български]]
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<source lang="cpp">
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#include <QtSql>
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#include <QtWidgets>
  
= How to Store and Retrieve an Image or File with SQLite =
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int main( int argc, char *argv[] )
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{
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    QApplication app( argc, argv );
  
Images or any files can be stored in a database. Here is one way to do it using the following steps:
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    // Set up database
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    QString dbName( "myDatabase.db3" );
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    QFile::remove( dbName ); // delete sqlite file if it exists from a previous run
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    QSqlDatabase db = QSqlDatabase::addDatabase( "QSQLITE" );
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    db.setDatabaseName( dbName );
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    db.open();
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    QSqlQuery query = QSqlQuery( db );
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    query.exec( "CREATE TABLE IF NOT EXISTS imgTable ( filename TEXT, imagedata BLOB )" );
  
1. Read the system file into a QByteArray.
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    // Generate an image (in this case a screenshot) and store it in a QByteArray
2. Store QByteArray as a Binary Large Object in database.
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    QScreen *screen = app.primaryScreen();
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    QPixmap inPixmap = screen->grabWindow( 0 );
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    QByteArray inByteArray;
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    QBuffer inBuffer( &inByteArray );
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    inBuffer.open( QIODevice::WriteOnly );
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    inPixmap.save( &inBuffer, "PNG" ); // write inPixmap into inByteArray in PNG format
  
For example :
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    // Alternatively, load an image file directly into a QByteArray
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    // QFile file("screenshot.png");
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    // if (!file.open(QIODevice::ReadOnly)) return;
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    // QByteArray inByteArray = file.readAll();
  
<code>
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    // Insert image bytes into the database
QFile file(fileName);
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    // Note: make sure to wrap the :placeholder in parenthesis
if (!file.open(QIODevice::ReadOnly)) return;
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    query.prepare( "INSERT INTO imgTable (filename, imagedata) VALUES ('screenshot.png', :imageData)" );
QByteArray byteArray = file.readAll();
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    query.bindValue( ":imageData", inByteArray );
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    if( !query.exec() )
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        qDebug() << "Error inserting image into table:\n" << query.lastError();
  
QSqlQuery query;
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    // Get image data back from database
query.prepare("INSERT INTO imgtable (imgdata) VALUES (?)");
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    if( !query.exec( "SELECT imagedata from imgTable" ))
query.addBindValue(byteArray);
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        qDebug() << "Error getting image from table:\n" << query.lastError();
query.exec();
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    query.first();
</code>
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    QByteArray outByteArray = query.value( 0 ).toByteArray();
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    QPixmap outPixmap = QPixmap();
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    outPixmap.loadFromData( outByteArray );
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    db.close();
  
Now, the image/file can be retrieved like any other data
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    // Display image
<code>
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    QLabel myLabel;
QSqlQuery query("SELECT imgdata FROM imgtable");
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    myLabel.setPixmap( outPixmap );
query.next();
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    myLabel.show();
QByteArray array = query.value(0).toByteArray();
 
</code>
 
  
Creating a QPixmap from QByteArray :
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    return app.exec();
<code>
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}
QPixmap pixmap = QPixmap();
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</source>
pixmap.loadFromData(array);
 
</code>
 
  
It is done. Now the pixmap can be used in a Button as icon or in label etc.
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[[Category:Snippets]]
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[[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();
}