Getting an image from mysql database (as BLOB field) through subclassed QSqlQueryMode

[MarkoSan]

I am working on Qt/QML app, which connects to mysql database and fetches data from it. Now, how do I fetch image from database (as BLOB field) using QSqlQueryModel? Now, I know how to connect to database, I've written simple read only subclassed QSqlQueryModel, I do know how to get the value of some field, but how do I get image and show it in some QML ListView? Does anyone has some experience and/or example with QQuickImageProvider, is this right way to go?

[anda_skoa]

Your model needs to return some string id for each image when its data() method is called by the view.
The view's delegate then needs to use that id to construct an "image://" URL.
Your image provider then needs to convert the BLOB data for that id to a QImage.

Cheers,
_

[MarkoSan]

Your model needs to return some string id for each image when its data() method is called by the view.
The view's delegate then needs to use that id to construct an "image://" URL.
Your image provider then needs to convert the BLOB data for that id to a QImage.

Cheers,
_

Can you please provide me some example?

[anda_skoa]

QVariant MyModel::data(const QModelIndex & index, int role) const
{
    if (role == ImageRole) {
        return QString::number(index.row());
    }
 
    /// other data
}
 
QImage MyModel::image(const QString &id) const
{
    int row = id.toInt();
 
    // load BLOB for image on row "row", return
}

QVariant MyModel::data(const QModelIndex & index, int role) const
{
    if (role == ImageRole) {
        return QString::number(index.row());
    }

    /// other data
}

QImage MyModel::image(const QString &id) const
{
    int row = id.toInt();

    // load BLOB for image on row "row", return
}

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Image {
    source: "image://mysqlimageprovider/" * model.image
}

Image {
    source: "image://mysqlimageprovider/" * model.image
}

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QImage MyImageProvider::requestImage(const QString &d, QSize *size, const QSize &requestedSize, bool requestedAutoTransform)
{
    QImage image = myModel->image(id);
    *size = image.size();
    return image;
}

QImage MyImageProvider::requestImage(const QString &d, QSize *size, const QSize &requestedSize, bool requestedAutoTransform)
{
    QImage image = myModel->image(id);
    *size = image.size();
    return image;
}

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You could even inherit your model from both the current base class and QQuickImageProvider.

Cheers,
_

[MarkoSan]

QVariant MyModel::data(const QModelIndex & index, int role) const
{
    if (role == ImageRole) {
        return QString::number(index.row());
    }
 
    /// other data
}
 
QImage MyModel::image(const QString &id) const
{
    int row = id.toInt();
 
    // load BLOB for image on row "row", return
}

QVariant MyModel::data(const QModelIndex & index, int role) const
{
    if (role == ImageRole) {
        return QString::number(index.row());
    }

    /// other data
}

QImage MyModel::image(const QString &id) const
{
    int row = id.toInt();

    // load BLOB for image on row "row", return
}

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Image {
    source: "image://mysqlimageprovider/" * model.image
}

Image {
    source: "image://mysqlimageprovider/" * model.image
}

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QImage MyImageProvider::requestImage(const QString &d, QSize *size, const QSize &requestedSize, bool requestedAutoTransform)
{
    QImage image = myModel->image(id);
    *size = image.size();
    return image;
}

QImage MyImageProvider::requestImage(const QString &d, QSize *size, const QSize &requestedSize, bool requestedAutoTransform)
{
    QImage image = myModel->image(id);
    *size = image.size();
    return image;
}

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You could even inherit your model from both the current base class and QQuickImageProvider.

Cheers,
_

Wow, superb idea! Will try asap!

[MarkoSan]

Hmm, it seems I've forgot a little about Qt models, here is my code, first header file:

#ifndef UEPEOPLEMODEL_H
#define UEPEOPLEMODEL_H
 
#include <QImage>
#include <QVariant>
#include <QStringList>
#include <QDebug>
#include <QHash>
#include <QByteArray>
#include <QtSql/QSqlError>
#include <QtSql/QSqlQueryModel>
#include <QtSql/QSqlRecord>
#include <QModelIndex>
#include <QQuickImageProvider>
 
#include "../settings/uedefaults.h"
 
class UePeopleModel : public QSqlQueryModel, QQuickImageProvider
{
    Q_OBJECT
 
/*
private:
    QHash<int, QByteArray> m_ueRoleNames;
 
    void ueGenerateRoleNames();
*/
 
public:
    UePeopleModel(QObject *parent=0);
    ~UePeopleModel();
 
    QVariant data(const QModelIndex &index,
                  int role) const Q_DECL_OVERRIDE;
//    void ueRefresh();
/*
    inline QHash<int, QByteArray> roleNames() const
        { return this->m_ueRoleNames; }
*/
 
public:
    static const int UePersonNameRole=Qt::UserRole+1;
    static const int UePersonImageRole=UePersonNameRole+1;
};
 
#endif // UEPEOPLEMODEL_H

#ifndef UEPEOPLEMODEL_H
#define UEPEOPLEMODEL_H

#include <QImage>
#include <QVariant>
#include <QStringList>
#include <QDebug>
#include <QHash>
#include <QByteArray>
#include <QtSql/QSqlError>
#include <QtSql/QSqlQueryModel>
#include <QtSql/QSqlRecord>
#include <QModelIndex>
#include <QQuickImageProvider>

#include "../settings/uedefaults.h"

class UePeopleModel : public QSqlQueryModel, QQuickImageProvider
{
    Q_OBJECT

/*
private:
    QHash<int, QByteArray> m_ueRoleNames;

    void ueGenerateRoleNames();
*/

public:
    UePeopleModel(QObject *parent=0);
    ~UePeopleModel();

    QVariant data(const QModelIndex &index,
                  int role) const Q_DECL_OVERRIDE;
//    void ueRefresh();
/*
    inline QHash<int, QByteArray> roleNames() const
        { return this->m_ueRoleNames; }
*/

public:
    static const int UePersonNameRole=Qt::UserRole+1;
    static const int UePersonImageRole=UePersonNameRole+1;
};

#endif // UEPEOPLEMODEL_H

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and its implementation:

#include "uepeoplemodel.h"
 
UePeopleModel::UePeopleModel(QObject* parent)
    : QSqlQueryModel(parent),
      QQuickImageProvider(QQmlImageProviderBase::Image,
                          0)
{
    QSqlDatabase db;
 
    if(!QSqlDatabase::connectionNames().contains(UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE,
                                                 Qt::CaseInsensitive))
    {
            db=QSqlDatabase::addDatabase(UePosDatabase::DATABASE_DRIVER,
                                         UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE);
    }   // if
 
    db.setHostName(/*this->uePosSettings()->ueDbHostname()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_HOSTNAME);
    db.setDatabaseName(/*this->uePosSettings()->ueDbName()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_NAME);
    db.setUserName(/*this->uePosSettings()->ueDbUser()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_USERNAME);
    db.setPassword(/*this->uePosSettings()->ueDbPassword()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_PASSWORD);
 
    if(db.open())
    {
        this->setQuery(UePosDatabase::UeSqlQueries::UeTablePeople::SQL_QUERY_GET_ALL_PEOPLE,
                       db);
        //this->ueGenerateRoleNames();
    }
    else
    {
        qDebug() << db.lastError().text();
    }
}   // default constructor
 
UePeopleModel::~UePeopleModel()
{
}   // default destructor
 
QVariant UePeopleModel::data(const QModelIndex &index,
                             int role) const
{
//    QVariant value;
 
//    if(role<Qt::UserRole)
//    {
//        value=QSqlQueryModel::data(index,
//                                   role);
//    }
//    else
//    {
//        int iColumnIndex=role-Qt::UserRole-1;
//        QModelIndex modelIndex=this->index(index.row(),
//                                           iColumnIndex);
 
//        value=QSqlQueryModel::data(modelIndex,
//                                   Qt::DisplayRole);
//    }   // if
 
//    return value;
 
    QVariant value=QSqlQueryModel::data(index,
                                        role);
 
    if(value.isValid()&&role==Qt::DisplayRole)
    {
        switch(index.column())
        {
            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_ID:
                return value.toInt();
 
            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_NAME:
                return value.toString();
 
            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_APPPASSWORD:
                return value.toString();
 
            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_CARD:
                return value.toString();
 
            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_IMAGE:
            {
                QImage image;
 
                image.loadFromData(value.toByteArray());
 
                return image;
            }   // case
 
            default:
                return value;
        }   // switch
    }   // if
 
    return QVariant();
}   // data
 
/*
void UePeopleModel::ueRefresh()
{
    this->setQuery(UePosDatabase::UeSqlQueries::UeTablePeople::SQL_QUERY_GET_ALL_PEOPLE);
}   // ueRefresh
*/
 
//void UePeopleModel::ueGenerateRoleNames()
//{
//    //this->roleNames().clear();
//    m_ueRoleNames.clear();
//    for(int iIndex=0; iIndex<this->record().count(); iIndex++)
//    {
///*
//        this->roleNames().insert(Qt::UserRole+1+iIndex,
//                                 this->record().fieldName(iIndex).toUtf8());
//*/
//        m_ueRoleNames.insert(Qt::UserRole+1+iIndex,
//                             this->record().fieldName(iIndex).toUtf8());
//    }   // for
//}   // ueGenerateRoleNames

#include "uepeoplemodel.h"

UePeopleModel::UePeopleModel(QObject* parent)
    : QSqlQueryModel(parent),
      QQuickImageProvider(QQmlImageProviderBase::Image,
                          0)
{
    QSqlDatabase db;

    if(!QSqlDatabase::connectionNames().contains(UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE,
                                                 Qt::CaseInsensitive))
    {
            db=QSqlDatabase::addDatabase(UePosDatabase::DATABASE_DRIVER,
                                         UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE);
    }   // if

    db.setHostName(/*this->uePosSettings()->ueDbHostname()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_HOSTNAME);
    db.setDatabaseName(/*this->uePosSettings()->ueDbName()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_NAME);
    db.setUserName(/*this->uePosSettings()->ueDbUser()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_USERNAME);
    db.setPassword(/*this->uePosSettings()->ueDbPassword()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_PASSWORD);

    if(db.open())
    {
        this->setQuery(UePosDatabase::UeSqlQueries::UeTablePeople::SQL_QUERY_GET_ALL_PEOPLE,
                       db);
        //this->ueGenerateRoleNames();
    }
    else
    {
        qDebug() << db.lastError().text();
    }
}   // default constructor

UePeopleModel::~UePeopleModel()
{
}   // default destructor

QVariant UePeopleModel::data(const QModelIndex &index,
                             int role) const
{
//    QVariant value;

//    if(role<Qt::UserRole)
//    {
//        value=QSqlQueryModel::data(index,
//                                   role);
//    }
//    else
//    {
//        int iColumnIndex=role-Qt::UserRole-1;
//        QModelIndex modelIndex=this->index(index.row(),
//                                           iColumnIndex);

//        value=QSqlQueryModel::data(modelIndex,
//                                   Qt::DisplayRole);
//    }   // if

//    return value;

    QVariant value=QSqlQueryModel::data(index,
                                        role);

    if(value.isValid()&&role==Qt::DisplayRole)
    {
        switch(index.column())
        {
            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_ID:
                return value.toInt();

            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_NAME:
                return value.toString();

            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_APPPASSWORD:
                return value.toString();

            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_CARD:
                return value.toString();

            case UePosDatabase::UeTableIndexes::UeTablePeople::INDEX_IMAGE:
            {
                QImage image;

                image.loadFromData(value.toByteArray());

                return image;
            }   // case

            default:
                return value;
        }   // switch
    }   // if

    return QVariant();
}   // data

/*
void UePeopleModel::ueRefresh()
{
    this->setQuery(UePosDatabase::UeSqlQueries::UeTablePeople::SQL_QUERY_GET_ALL_PEOPLE);
}   // ueRefresh
*/

//void UePeopleModel::ueGenerateRoleNames()
//{
//    //this->roleNames().clear();
//    m_ueRoleNames.clear();
//    for(int iIndex=0; iIndex<this->record().count(); iIndex++)
//    {
///*
//        this->roleNames().insert(Qt::UserRole+1+iIndex,
//                                 this->record().fieldName(iIndex).toUtf8());
//*/
//        m_ueRoleNames.insert(Qt::UserRole+1+iIndex,
//                             this->record().fieldName(iIndex).toUtf8());
//    }   // for
//}   // ueGenerateRoleNames

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Am I using Qt:isplayRole in right way or should I implement custom roles? And how do I then use this data()method in qml?

[anda_skoa]

You can use Qt:isplayRole, it is mapped by default to "model.display" in QML.

However, you need to keep in mind that the QtQuick views, e.g. ListView or TableView, do not deal with model columns, only rows, so you will need custom roles anyway.

I would suggest to use custom roles for all columns and not use Qt:isplayRole other than maybe for debugging (e.g. with a QWidget based table view).

So in your data() method you first need to map the role to a column and then proceed with quering the data from the base class.

Cheers,
_

[MarkoSan]

Ok, I am a little lost now. I've done this:

#ifndef UEPEOPLEMODEL_H
#define UEPEOPLEMODEL_H
 
#include <QImage>
#include <QVariant>
#include <QStringList>
#include <QDebug>
#include <QHash>
#include <QByteArray>
#include <QtSql/QSqlError>
#include <QtSql/QSqlQueryModel>
#include <QtSql/QSqlRecord>
#include <QModelIndex>
#include <QQuickImageProvider>
 
#include "../settings/uedefaults.h"
 
class UePeopleModel : public QSqlQueryModel, QQuickImageProvider
{
    Q_OBJECT
 
public:
    UePeopleModel(QObject *parent=0);
    ~UePeopleModel();
 
    QVariant data(const QModelIndex &index,
                  int role) const Q_DECL_OVERRIDE;
    QImage image(const QString &id) const;
    QImage requestImage(const QString &id,
                        QSize *size,
                        const QSize &requestedSize);
 
public:
    static const int UePersonNameRole=Qt::UserRole+1;
    static const int UePersonImageRole=UePersonNameRole+1;
};
 
#endif // UEPEOPLEMODEL_H

#ifndef UEPEOPLEMODEL_H
#define UEPEOPLEMODEL_H

#include <QImage>
#include <QVariant>
#include <QStringList>
#include <QDebug>
#include <QHash>
#include <QByteArray>
#include <QtSql/QSqlError>
#include <QtSql/QSqlQueryModel>
#include <QtSql/QSqlRecord>
#include <QModelIndex>
#include <QQuickImageProvider>

#include "../settings/uedefaults.h"

class UePeopleModel : public QSqlQueryModel, QQuickImageProvider
{
    Q_OBJECT

public:
    UePeopleModel(QObject *parent=0);
    ~UePeopleModel();

    QVariant data(const QModelIndex &index,
                  int role) const Q_DECL_OVERRIDE;
    QImage image(const QString &id) const;
    QImage requestImage(const QString &id,
                        QSize *size,
                        const QSize &requestedSize);

public:
    static const int UePersonNameRole=Qt::UserRole+1;
    static const int UePersonImageRole=UePersonNameRole+1;
};

#endif // UEPEOPLEMODEL_H

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and implementation:

#include "uepeoplemodel.h"
 
UePeopleModel::UePeopleModel(QObject* parent)
    : QSqlQueryModel(parent),
      QQuickImageProvider(QQmlImageProviderBase::Image,
                          QQmlImageProviderBase::ForceAsynchronousImageLoading)
{
    QSqlDatabase db;
 
    if(!QSqlDatabase::connectionNames().contains(UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE,
                                                 Qt::CaseInsensitive))
    {
            db=QSqlDatabase::addDatabase(UePosDatabase::DATABASE_DRIVER,
                                         UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE);
    }   // if
 
    db.setHostName(/*this->uePosSettings()->ueDbHostname()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_HOSTNAME);
    db.setDatabaseName(/*this->uePosSettings()->ueDbName()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_NAME);
    db.setUserName(/*this->uePosSettings()->ueDbUser()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_USERNAME);
    db.setPassword(/*this->uePosSettings()->ueDbPassword()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_PASSWORD);
 
    if(db.open())
    {
        this->setQuery(UePosDatabase::UeSqlQueries::UeTablePeople::SQL_QUERY_GET_ALL_PEOPLE,
                       db);
        //this->ueGenerateRoleNames();
    }
    else
    {
        qDebug() << db.lastError().text();
    }
}   // default constructor
 
UePeopleModel::~UePeopleModel()
{
}   // default destructor
 
QVariant UePeopleModel::data(const QModelIndex &index,
                             int role) const
{
    QVariant value=QSqlQueryModel::data(index,
                                        role);
    if(value.isValid())
    {
        switch(role)
        {
            case UePeopleModel::UePersonNameRole:
            {
                return value.toString();
            }   // case
 
            case UePeopleModel::UePersonImageRole:
            {
                return QString::number(index.row());
            }   // case
 
            default:
                value=QVariant();
        }   // switch
    }   // if
 
    return value;
}   // data
 
QImage UePeopleModel::image(const QString &id) const
{
    int iRow=id.toInt();
}   // image
 
QImage UePeopleModel::requestImage(const QString &id,
                                   QSize *size,
                                   const QSize &requestedSize)
{
    QImage image=this->image(id);
 
    *size = image.size();
 
    return image;
}   // requestImage

#include "uepeoplemodel.h"

UePeopleModel::UePeopleModel(QObject* parent)
    : QSqlQueryModel(parent),
      QQuickImageProvider(QQmlImageProviderBase::Image,
                          QQmlImageProviderBase::ForceAsynchronousImageLoading)
{
    QSqlDatabase db;

    if(!QSqlDatabase::connectionNames().contains(UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE,
                                                 Qt::CaseInsensitive))
    {
            db=QSqlDatabase::addDatabase(UePosDatabase::DATABASE_DRIVER,
                                         UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE);
    }   // if

    db.setHostName(/*this->uePosSettings()->ueDbHostname()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_HOSTNAME);
    db.setDatabaseName(/*this->uePosSettings()->ueDbName()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_NAME);
    db.setUserName(/*this->uePosSettings()->ueDbUser()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_USERNAME);
    db.setPassword(/*this->uePosSettings()->ueDbPassword()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_PASSWORD);

    if(db.open())
    {
        this->setQuery(UePosDatabase::UeSqlQueries::UeTablePeople::SQL_QUERY_GET_ALL_PEOPLE,
                       db);
        //this->ueGenerateRoleNames();
    }
    else
    {
        qDebug() << db.lastError().text();
    }
}   // default constructor

UePeopleModel::~UePeopleModel()
{
}   // default destructor

QVariant UePeopleModel::data(const QModelIndex &index,
                             int role) const
{
    QVariant value=QSqlQueryModel::data(index,
                                        role);
    if(value.isValid())
    {
        switch(role)
        {
            case UePeopleModel::UePersonNameRole:
            {
                return value.toString();
            }   // case

            case UePeopleModel::UePersonImageRole:
            {
                return QString::number(index.row());
            }   // case

            default:
                value=QVariant();
        }   // switch
    }   // if

    return value;
}   // data

QImage UePeopleModel::image(const QString &id) const
{
    int iRow=id.toInt();
}   // image

QImage UePeopleModel::requestImage(const QString &id,
                                   QSize *size,
                                   const QSize &requestedSize)
{
    QImage image=this->image(id);

    *size = image.size();

    return image;
}   // requestImage

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Now what?

[anda_skoa]

Couple of things:

- in order to be able to use this class as a QQuickImageProvider, it needs to have a "is-a" relation ship, i.e. publically inherit from QQuickImageProvider
- in data() it doesn't make sense to use the role as given to query the base class, after all these roles will most often be your custom roles and have no meaning for the base class
- you are missing the roleNames() override that returns the mapping of role names (used in QML) to role numbers (using in the C++ API).

Cheers,
_

[MarkoSan]

Couple of things:

- in order to be able to use this class as a QQuickImageProvider, it needs to have a "is-a" relation ship, i.e. publically inherit from QQuickImageProvider
- in data() it doesn't make sense to use the role as given to query the base class, after all these roles will most often be your custom roles and have no meaning for the base class
- you are missing the roleNames() override that returns the mapping of role names (used in QML) to role numbers (using in the C++ API).

Cheers,
_

Well, class is publicly inherited from QQuickImageProvider:

class UePeopleModel : public QSqlQueryModel, QQuickImageProvider

class UePeopleModel : public QSqlQueryModel, QQuickImageProvider

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I've upgraded function data(), is now ok:

QVariant UePeopleModel::data(const QModelIndex &index,
                             int role) const
{
    QVariant value=QSqlQueryModel::data(index,
                                        role);
    if(value.isValid())
    {
        switch(role)
        {
            case ueRoleName:
            {
                return value.toString();
            }   // case
 
            case ueRoleImage:
            {
                return QString::number(index.row());
            }   // case
 
            default:
                value=QVariant();
        }   // switch
    }   // if
 
    return value;
}   // data

QVariant UePeopleModel::data(const QModelIndex &index,
                             int role) const
{
    QVariant value=QSqlQueryModel::data(index,
                                        role);
    if(value.isValid())
    {
        switch(role)
        {
            case ueRoleName:
            {
                return value.toString();
            }   // case

            case ueRoleImage:
            {
                return QString::number(index.row());
            }   // case

            default:
                value=QVariant();
        }   // switch
    }   // if

    return value;
}   // data

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But what do I have to put inside method UePeopleModel::image?

Sincerely yours,
Marko

[anda_skoa]

Well, class is publicly inherited from QQuickImageProvider:

class UePeopleModel : public QSqlQueryModel, QQuickImageProvider

class UePeopleModel : public QSqlQueryModel, QQuickImageProvider

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Nope. Unless your code looks different in reality, this is a private inheritance

I've upgraded function data(), is now ok:

Nope, see my last comment.

But what do I have to put inside method UePeopleModel::image?

You get the BLOB from the base class for the given row and then load it into a QImage.
If the BLOB is data in a format known to Qt, then you can probably use QImage::loadFromData().

Cheers,
_