ListView QML的RoleName中的QSqlQueryModel参考错误 [英] QSqlQueryModel reference error in roleName for ListView QML

问题描述

我想从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。但是每列中的数据我都有一个ReferenceError试图获取列名
cpp代码：

I want to get the model from my SQlite Database, when I set the query in the QSqlQueryModel I can get the number of rows, number of columns, etc. But the data inside each column I have a ReferenceError trying to get the name of the column The cpp code:

//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();

这就是我从输出
中得到的内容

And this is what I get from the output

这就是我在QML中的ListView中的内容：

This is what I have in my ListView in QML:

ListView {
    id: listaUsuarios
    model: sqlModel
    delegate:
    Text{
        anchors.fill: parent
        text: nombre
     }
}

推荐答案

如何观察表的字段不是角色，因此无法从QML访问它们，因此要访问它们，必须将字段名称添加为角色，为此必须覆盖该类：

How to observe the fields of the table are not roles, so they can not be accessed from QML, so to be accessed, the name of the fields must be added as a role, for this the class must be overwritten:

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;
    }
};

示例：

#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：

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