Inconsistent view when removing a single row from QSqlTableModel in Qml - c++

Question

What I am trying to do ?
I am trying to create a list of users whoes data come from a database. And I want to use the concept of model/view programming to implement this. Morever I want to apply various operations on this list such as:
Displaying a list
Removing an item from the list
Adding an item to the list
Sorting the list
What is the problem ?
The first operation ( Displaying the list ) was easy but the second ( Removing an item from the list ) seems to impose inconsistency between the model and the view. No matter which item you select for deletion the view always shows two items have been deleted ( when in fact only the selected item has been deleted by the model ). The two items deleted by the view are the selected item and the last item. Why does it always delete the last item ? How would I fix this ?
Here is my code so far:
usermodel.h:
class UserModel : public QAbstractListModel {
Q_OBJECT
public:
UserModel(QObject *parent = nullptr);
int rowCount(const QModelIndex &parent = QModelIndex()) const override;
QVariant data(const QModelIndex &index, int role) const override;
bool removeRows(int pos, int row, const QModelIndex &parent = QModelIndex()) override;
Q_INVOKABLE bool del_row(int);
// initialize and setup the database
static bool createConnection() {
db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("Test");
if (!db.open()) return false;
QSqlQuery q;
QStringList t = db.tables();
// create table users if there is none
if (!t.contains("users", Qt::CaseInsensitive)){
if (!q.exec("create table users (id int primary key, firstname varchar(20))")){
return false;
}
}
q.exec("select * from users");
// insert new records when there is none
if (!q.first()){
q.exec("insert into users values(1, 'Danny')");
q.exec("insert into users values(2, 'Christine')");
q.exec("insert into users values(3, 'Lars')");
q.exec("insert into users values(4, 'Alex')");
}
}
private:
QSqlTableModel *model; // internal data store for models
static QSqlDatabase db;
};
usermode.cpp:
QSqlDatabase UserModel::db;
UserModel::UserModel(QObject *parent) : QAbstractListModel (parent) {
createConnection();
model = new QSqlTableModel(this, db);
model->setTable("users");
model->select();
}
int UserModel::rowCount(const QModelIndex &/*parent*/) const {
return model->rowCount();
}
QVariant UserModel::data(const QModelIndex &index, int role) const {
// This allows me to return more than one column data when not permitted
QJsonObject u_data;
u_data.insert("id", model->record(index.row()).value(0).toInt());
u_data.insert("name", model->record(index.row()).value(1).toString());
if (role == Qt::DisplayRole)
return u_data;
return QVariant();
}
bool UserModel::del_row(int row){
return removeRows(row, 1);
}
bool UserModel::removeRows(int pos, int rows, const QModelIndex &/*parent*/){
bool response;
int first = pos, last = pos + rows - 1;
beginRemoveRows(QModelIndex(), first, last);
response = model->removeRow(first, QModelIndex());
endRemoveRows();
return response;
}
main.qml:
ApplicationWindow {
visible: true
width: 640
height: 480
ListView {
anchors.fill: parent
delegate: SwipeDelegate {
width: parent.width
height: 50
text: user_model.data(user_model.index(index, 0), 0)["name"]
onClicked: user_model.del_row(model.index)
}
model: UserModel { id: user_model }
}
}
Note: Please don't provide any link in the replay as I may not be able to access them because the Government here has blocked most of the sites and whitelisted few sites ( stackoverflow is one of them ).

Answer 1

I don't see the need to create a model that is a wrapper of another model, so in this first solution I will propose a solution using the QSqlTableModel class directly. On the other hand when using removeRows() the row is not deleted but you must update the database using the select() method:
usermodel.h
#ifndef USERMODEL_H
#define USERMODEL_H
#include <QSqlTableModel>
class UserModel : public QSqlTableModel
{
Q_OBJECT
public:
UserModel(QObject *parent = nullptr, QSqlDatabase db = QSqlDatabase());
QVariant data(const QModelIndex &index, int role) const;
QHash<int, QByteArray> roleNames() const;
Q_INVOKABLE void removeRow(int row);
};
#endif // USERMODEL_H
usermodel.cpp
#include "usermodel.h"
#include <QSqlRecord>
UserModel::UserModel(QObject *parent, QSqlDatabase db): QSqlTableModel(parent, db){
setTable("users");
select();
}
QVariant UserModel::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> UserModel::roleNames() const{
QHash<int, QByteArray> roles;
for (int i = 0; i < record().count(); i ++) {
roles.insert(Qt::UserRole + i + 1, record().fieldName(i).toUtf8());
}
return roles;
}
void UserModel::removeRow(int row){
removeRows(row, 1, QModelIndex());
select();
}
main.cpp
#include "usermodel.h"
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QSqlQuery>
static bool createConnection() {
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("Test");
if (!db.open()) return false;
QSqlQuery q;
QStringList t = db.tables();
// create table users if there is none
if (!q.exec("CREATE TABLE IF NOT EXISTS users (id int primary key, firstname varchar(20))")){
return false;
}
q.exec("insert into users values(1, 'Danny')");
q.exec("insert into users values(2, 'Christine')");
q.exec("insert into users values(3, 'Lars')");
q.exec("insert into users values(4, 'Alex')");
return true;
}
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
qmlRegisterType<UserModel>("Database", 1, 0, "UserModel");
QGuiApplication app(argc, argv);
if(!createConnection())
return -1;
QQmlApplicationEngine engine;
const QUrl url(QStringLiteral("qrc:/main.qml"));
QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
&app, [url](QObject *obj, const QUrl &objUrl) {
if (!obj && url == objUrl)
QCoreApplication::exit(-1);
}, Qt::QueuedConnection);
engine.load(url);
return app.exec();
}
main.qml
import QtQuick 2.14
import QtQuick.Controls 2.14
import Database 1.0
ApplicationWindow {
visible: true
width: 640
height: 480
ListView {
anchors.fill: parent
delegate: SwipeDelegate {
width: parent.width
height: 50
text: model.firstname
onClicked: user_model.removeRow(model.index)
}
model: UserModel { id: user_model }
}
}