C++ ListView QML的roleName中的QSqlQueryModel引用错误

我想从我的SQlite数据库中获取模型，当我在QSqlQueryModel中设置查询时，我可以获取行数、列数等。但是每个列中的数据在尝试获取列的名称时出现了引用错误 cpp代码：

//data base users
QSqlQueryModel *sqlModel = new QSqlQueryModel();
sqlModel->setQuery("SELECT usuarios.nombre FROM usuarios");

sqlModel->setHeaderData(0,Qt::Horizontal, QObject::tr("nombre"));
qDebug() << "ROL: " << sqlModel->roleNames();
qDebug() << "number of rows: " << sqlModel->rowCount();
qDebug() << "number of columns: " << sqlModel->columnCount();
qDebug() << "HEADER: " << sqlModel->headerData(1, Qt::Horizontal).toString();

---

如何观察表中的字段不是角色，因此无法从QML访问它们，因此要访问，必须将字段的名称添加为角色，为此必须覆盖类：

class SqlQueryModel: public QSqlQueryModel{
public:
    using QSqlQueryModel::QSqlQueryModel;
    QVariant data(const QModelIndex &index, int role) const
    {
        QVariant value;
        if (index.isValid()) {
            if (role < Qt::UserRole) {
                value = QSqlQueryModel::data(index, role);
            } else {
                int columnIdx = role - Qt::UserRole - 1;
                QModelIndex modelIndex = this->index(index.row(), columnIdx);
                value = QSqlQueryModel::data(modelIndex, Qt::DisplayRole);
            }
        }
        return value;
    }
    QHash<int, QByteArray> roleNames() const
    {
        QHash<int, QByteArray> roles = QSqlQueryModel::roleNames();
        for (int i = 0; i < this->record().count(); i ++) {
            roles.insert(Qt::UserRole + i + 1, record().fieldName(i).toUtf8());
        }
        return roles;
    }
};

例如：

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

#include <QSqlDatabase>
#include <QSqlQuery>
#include <QSqlQueryModel>
#include <QSqlRecord>
#include <QDebug>

static bool createConnection()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName(":memory:");
    if (!db.open()) {
        qDebug()<<"Unable to establish a database connection.\n"
                  "This example needs SQLite support. Please read "
                  "the Qt SQL driver documentation for information how "
                  "to build it.\n\n"
                  "Click Cancel to exit.";
        return false;
    }

    QSqlQuery query;
    query.exec("create table usuarios (ID INTEGER PRIMARY KEY AUTOINCREMENT, "
               "nombre VARCHAR(20), apellido VARCHAR(20))");
    query.exec("insert into usuarios values(1, 'Danny', 'Young')");
    query.exec("insert into usuarios values(2, 'Christine', 'Holand')");
    query.exec("insert into usuarios values(3, 'Lars', 'Gordon')");
    query.exec("insert into usuarios values(4, 'Roberto', 'Robitaille')");
    query.exec("insert into usuarios values(5, 'Maria', 'Papadopoulos')");
    return true;
}

class SqlQueryModel: public QSqlQueryModel{
public:
    using QSqlQueryModel::QSqlQueryModel;
    QVariant data(const QModelIndex &index, int role) const
    {
        QVariant value;
        if (index.isValid()) {
            if (role < Qt::UserRole) {
                value = QSqlQueryModel::data(index, role);
            } else {
                int columnIdx = role - Qt::UserRole - 1;
                QModelIndex modelIndex = this->index(index.row(), columnIdx);
                value = QSqlQueryModel::data(modelIndex, Qt::DisplayRole);
            }
        }
        return value;
    }
    QHash<int, QByteArray> roleNames() const
    {
        QHash<int, QByteArray> roles = QSqlQueryModel::roleNames();
        for (int i = 0; i < this->record().count(); i ++) {
            roles.insert(Qt::UserRole + i + 1, record().fieldName(i).toUtf8());
        }
        return roles;
    }
};

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);
    if(!createConnection())
        return -1;

    SqlQueryModel sqlModel;
    sqlModel.setQuery("SELECT usuarios.nombre FROM usuarios");
    qDebug() << sqlModel.roleNames();

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty("sqlModel", &sqlModel);
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

输出：

---

没错，我以前看过一个例子，但你得到的关键是覆盖roleName方法。谢谢大家=DDo您知道如果在数据库中插入数据，您能实时看到插入的内容吗？

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

#include <QSqlDatabase>
#include <QSqlQuery>
#include <QSqlQueryModel>
#include <QSqlRecord>
#include <QDebug>

static bool createConnection()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName(":memory:");
    if (!db.open()) {
        qDebug()<<"Unable to establish a database connection.\n"
                  "This example needs SQLite support. Please read "
                  "the Qt SQL driver documentation for information how "
                  "to build it.\n\n"
                  "Click Cancel to exit.";
        return false;
    }

    QSqlQuery query;
    query.exec("create table usuarios (ID INTEGER PRIMARY KEY AUTOINCREMENT, "
               "nombre VARCHAR(20), apellido VARCHAR(20))");
    query.exec("insert into usuarios values(1, 'Danny', 'Young')");
    query.exec("insert into usuarios values(2, 'Christine', 'Holand')");
    query.exec("insert into usuarios values(3, 'Lars', 'Gordon')");
    query.exec("insert into usuarios values(4, 'Roberto', 'Robitaille')");
    query.exec("insert into usuarios values(5, 'Maria', 'Papadopoulos')");
    return true;
}

class SqlQueryModel: public QSqlQueryModel{
public:
    using QSqlQueryModel::QSqlQueryModel;
    QVariant data(const QModelIndex &index, int role) const
    {
        QVariant value;
        if (index.isValid()) {
            if (role < Qt::UserRole) {
                value = QSqlQueryModel::data(index, role);
            } else {
                int columnIdx = role - Qt::UserRole - 1;
                QModelIndex modelIndex = this->index(index.row(), columnIdx);
                value = QSqlQueryModel::data(modelIndex, Qt::DisplayRole);
            }
        }
        return value;
    }
    QHash<int, QByteArray> roleNames() const
    {
        QHash<int, QByteArray> roles = QSqlQueryModel::roleNames();
        for (int i = 0; i < this->record().count(); i ++) {
            roles.insert(Qt::UserRole + i + 1, record().fieldName(i).toUtf8());
        }
        return roles;
    }
};

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);
    if(!createConnection())
        return -1;

    SqlQueryModel sqlModel;
    sqlModel.setQuery("SELECT usuarios.nombre FROM usuarios");
    qDebug() << sqlModel.roleNames();

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty("sqlModel", &sqlModel);
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}