QSqlQuery::QSqlQueryModel内的值::data返回空数据

我已经将QSqlQueryModel子类化，命名为UeOrdersModel，它基于以下SQL语句从数据库中提取数据：

SELECT ORDERS.USER_ID, 
       PEOPLE.NAME, 
       PLACE_ID, 
       PLACES.NAME,  
       PRODUCT_ID, 
       PRODUCTS.IMAGE, 
       PRODUCTS.NAME, 
       PRODUCTS.PRICESELL, 
       TAXES.RATE, 
       ORDERS.PRODUCT_QUANTITY 
FROM ORDERS 
JOIN PEOPLE 
ON ORDERS.USER_ID=PEOPLE.ID 
JOIN PRODUCTS 
ON ORDERS.PRODUCT_ID=PRODUCTS.ID 
JOIN PLACES 
ON ORDERS.PLACE_ID=PLACES.ID 
JOIN TAXCATEGORIES 
ON PRODUCTS.TAXCAT=TAXCATEGORIES.ID 
JOIN TAXES 
ON TAXCATEGORIES.ID=TAXES.ID 
WHERE ORDERS.USER_ID="15a2a62b-2a95-4d88-b0ad-d98001d730b4" 
  AND ORDERS.PLACE_ID="1";  

这里是我数据库的phpmyadmin输出：

╔══════════════════════════════════════╦═══════════╦══════════╦════════╦══════════════════════════════════════╦═══════╦═══════════════════╦═══════════════╦═══════╦══════════════════╗
║               USER_ID                ║   NAME    ║ PLACE_ID ║  NAME  ║              PRODUCT_ID              ║ IMAGE ║       NAME        ║   PRICESELL   ║ RATE  ║ PRODUCT_QUANTITY ║
╠══════════════════════════════════════╬═══════════╬══════════╬════════╬══════════════════════════════════════╬═══════╬═══════════════════╬═══════════════╬═══════╬══════════════════╣
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ eda6eaa3-fb7d-4470-8890-9b05aaf97fb6 ║ NULL  ║ Test product 1991 ║ 25            ║ 0     ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 8d307531-afe5-4746-a1f1-be5a743d453f ║ NULL  ║ Test product 1761 ║ 1,8264840183  ║ 0,095 ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 158e427c-11df-49b8-8d39-bfeff97c8f91 ║ NULL  ║ Test product 1333 ║ 1,6393442623  ║ 0,22  ║                6 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 2890fc4f-2e59-4c34-b838-b43b0dceb145 ║ NULL  ║ Test product 33   ║ 1,6393442623  ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 3b12cb57-0ecd-48e6-9c78-8b1715a365d5 ║ NULL  ║ Test product 34   ║ 1,6393442623  ║ 0,22  ║                2 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 3e72f6dc-baf5-4872-a42c-03b5a2748339 ║ NULL  ║ Test product 75   ║ 12,2950819672 ║ 0,22  ║                3 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 5e02ff9c-dcb3-42b1-a04e-f3728d06af3b ║ NULL  ║ Test product 20   ║ 1,6393442623  ║ 0,22  ║               12 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 67d44180-02c5-40b4-8c60-deebc99c1909 ║ NULL  ║ Test product 19   ║ 2,868852459   ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 6951109f-ae14-4691-b3b9-c64f11059780 ║ NULL  ║ Test product 18   ║ 1,6393442623  ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 7c007b66-2429-4e28-8bc0-8a15e595c606 ║ NULL  ║ Test product 52   ║ 1,6393442623  ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 7e43ff6a-80d9-4669-8600-a57f6ff030f7 ║ NULL  ║ Test product 12   ║ 1,6393442623  ║ 0,22  ║                6 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ 9ab29108-b058-48a3-b012-4c6684470217 ║ NULL  ║ Test product 13   ║ 2,7049180328  ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ a549b305-6a34-4d3a-b53c-63a93a2dea4a ║ NULL  ║ Test product 96   ║ 0,0819672131  ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ ba9d3fd6-2ed6-4eba-8f4e-4b550074b469 ║ NULL  ║ Test product 120  ║ 1,0655737705  ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ c23d03eb-dcf9-4757-bdad-161226753492 ║ NULL  ║ Test product 5    ║ 1,8852459016  ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ c30ceddf-2d89-492b-a5c3-defbe4999dd2 ║ NULL  ║ Test product 4    ║ 12,2950819672 ║ 0,22  ║                1 ║
║ 15a2a62b-2a95-4d88-b0ad-d98001d730b4 ║ Test User ║        1 ║ Miza 1 ║ e60ed145-5bbd-40e5-84f0-0ad8e63515d3 ║ NULL  ║ Test product 12   ║ 1,0655737705  ║ 0,22  ║                1 ║
╚══════════════════════════════════════╩═══════════╩══════════╩════════╩══════════════════════════════════════╩═══════╩═══════════════════╩═══════════════╩═══════╩══════════════════╝

正如我们所看到的，SQL语句本身并不是问题，因为它执行时没有错误。然而，当程序流进入子类QSqlQueryModel::data()方法时，我得到的只是每个该死角色的空字符串。我已经对数据库连接进行了三重检查，连接正常，执行查询没有问题，我再也没有什么该死的想法了。有人能给我一些提示吗？这是UeOrdersModel标题：

#ifndef UEORDERSMODEL_H
#define UEORDERSMODEL_H
#include <QObject>
#include <QSqlQueryModel>
#include <QQuickImageProvider>
#include <QObject>
#include <QSqlRecord>
#include <QSqlQuery>
#include <QList>
#include <QDebug>
#include <QSqlError>
#include <QSqlField>
#include "../settings/uedefaults.h"
#include "../core/uedatabaseconnectionstatus.h"
#include "../core/uetypes.h"
#include "../database/ueuserrecord.h"
class UeOrdersModel : public QSqlQueryModel,
                      public QQuickImageProvider
{
    Q_OBJECT
    friend class UeApplicationStatus;
private:
    QString m_ueUserId;
    QString m_uePlaceId;
    QString m_ueUserName;
    QString m_uePlaceName;
    QSqlDatabase m_ueDb;
    QSqlDatabase ueDatabase() const
        { return this->m_ueDb; }
    void ueSetDatabase(const QSqlDatabase& database)
        { this->m_ueDb=database; }
    void queryChange();
public:
    explicit UeOrdersModel(QObject *parent = 0,
                           const QString& userId="",
                           const QString& placeId="",
                           const QString &userName="",
                           const QString &placeName="");
    ~UeOrdersModel();
    inline QString ueUserId() const
        { return this->m_ueUserId; }
    inline QString uePlaceId() const
        { return this->m_uePlaceId; }
    inline QString ueUserName() const
        { return this->m_ueUserName; }
    inline QString uePlaceName() const
        { return this->m_uePlaceName; }
    inline void ueSetUserId(const QString& userId)
        { this->m_ueUserId=userId; }
    inline void ueSetPlaceId(const QString& placeId)
        { this->m_uePlaceId=placeId; }
    inline void ueSetUserName(const QString& userName)
        { this->m_ueUserName=userName; }
    inline void ueSetPlaceName(const QString& placeName)
        { this->m_uePlaceName=placeName; }
    QVariant data(const QModelIndex &index,
                  int role=Qt::DisplayRole) const Q_DECL_OVERRIDE;
    QImage requestImage(const QString &id,
                        QSize *size,
                        const QSize &requestedSize);
    UeTypeRoles roleNames() const;
    int rowCount(const QModelIndex &parent) const;
    int columnCount(const QModelIndex &parent) const;
    Q_INVOKABLE QVariantMap get(int row);
    void ueConnectToDatabase(const QString& userId,
                             const QString& placeId);
    Q_INVOKABLE bool ueAddOrder(const QString& userId,
                                       const QString& placeId,
                                       const QString& productId,
                                       const QString& quantity);
public:
    static const int ueRoleUserId=Qt::UserRole+1;
    static const int ueRoleUserName=Qt::UserRole+2;
    static const int ueRolePlaceId=Qt::UserRole+3;
    static const int ueRolePlaceName=Qt::UserRole+4;
    static const int ueRoleProductId=Qt::UserRole+5;
    static const int ueRoleProductImage=Qt::UserRole+6;
    static const int ueRoleProductName=Qt::UserRole+7;
    static const int ueRoleProductPriceSell=Qt::UserRole+8;
    static const int ueRoleProductVatRate=Qt::UserRole+9;
    static const int ueRoleProductQuantity=Qt::UserRole+10;
    static const int ueRoleOrderAmountWithoutVAT=Qt::UserRole+11;
    static const int ueRoleOrderAmountWithVAT=Qt::UserRole+12;
signals:
    void ueSignalDatabaseConnectionChanged(const UeDatabaseConnectionStatus::UeTypeDatabaseConnectionStatus& newStatus);
public slots:
    Q_INVOKABLE void ueSlotRefreshOrdersData(const QString& userId,
                                             const QString& placeId);
};
#endif // UEORDERSMODEL_H

及其实现：

#include "ueordersmodel.h"
UeOrdersModel::UeOrdersModel(QObject *parent,
                             const QString& userId,
                             const QString& placeId,
                             const QString& userName,
                             const QString& placeName)
    : QSqlQueryModel(parent),
      QQuickImageProvider(QQmlImageProviderBase::Image,
                          QQmlImageProviderBase::ForceAsynchronousImageLoading)
{
    this->ueSetUserId(userId);
    this->ueSetPlaceId(placeId);
    this->ueSetUserName(userName);
    this->ueSetPlaceName(placeName);
}   // constructor
UeOrdersModel::~UeOrdersModel()
{
}   // destructor
QVariant UeOrdersModel::data(const QModelIndex &index,
                             int role) const
{
    qDebug() << "(UeOrdersModel::data) this->query().lastQuery(): " << this->query().lastQuery()
             << "n"
             << "(UeOrdersModel::data) this->query().executedQuery(): " << this->query().executedQuery()
             << "n"
             << "(UeOrdersModel::data) this->query().isValid(): " << this->query().isValid();
    bool result=false;
    if(!this->query().isValid())
    {
        if(this->query().isActive())
            if(this->query().isSelect())
                    result=this->query().first();
    }
    if(index.isValid()&&index.row()>=0&&index.column()>=0&&this->record().isEmpty()==false&&this->query().isValid())
    {
        switch(role)
        {
            case ueRoleUserId:
            {
                return this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_USERID).toString();
            } break;
            case ueRoleUserName:
            {
                return this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_USERNAME).toString();
            } break;
            case ueRolePlaceId:
            {
                return this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PLACEID).toString();
            } break;
            case ueRolePlaceName:
            {
                return this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PLACENAME).toString();
            } break;
            case ueRoleProductId:
            {
                return this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCTID).toString();
            } break;
            case ueRoleProductImage:
            {
                return this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCTIMAGE).toString();
            } break;
            case ueRoleProductName:
            {
                return this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCTNAME).toString();
            } break;
            case ueRoleProductPriceSell:
            {
                return QString::number(this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_PRICESELL).toDouble());
            } break;
            case ueRoleProductVatRate:
            {
                return QString::number(this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_VATRATE).toDouble());
            } break;
            case ueRoleProductQuantity:
            {
                return QString::number(this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_QUANTITY).toUInt());
            } break;
            case ueRoleOrderAmountWithoutVAT:
            {
                return QString::number(this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_QUANTITY).toUInt()*
                                       this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_PRICESELL).toDouble());
            } break;
            case ueRoleOrderAmountWithVAT:
            {
                return QString::number(this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_QUANTITY).toUInt()*
                                      (this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_PRICESELL).toDouble()+
                                      (this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_PRICESELL).toDouble()*
                                       this->record(index.row()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCT_VATRATE).toDouble())));
            } break;
            default:
            {
                return QVariant();
            } break;    // default
        }   // switch
    }   // if
    return QVariant();
}   // data
QImage UeOrdersModel::requestImage(const QString &id,
                                   QSize *size,
                                   const QSize &requestedSize)
{
    Q_UNUSED(size)
    Q_UNUSED(requestedSize);
    QImage image=QImage::fromData(this->record(id.toInt()).value(UePosDatabase::UeQueryIndexes::QUERY_GET_ORDERS_FILTERED_BY_USERNAME_PLACENAME::INDEX_PRODUCTIMAGE).toByteArray(),
                                  "PNG");
    if(image.isNull())
    {
        image=QImage(":/ueIcons/icons/ueGenericProduct.png");
    }
    return image.scaled(UeDefaults::UeGraphics::UeProductImageSize::IMAGE_WIDTH,
                        UeDefaults::UeGraphics::UeProductImageSize::IMAGE_HEIGHT,
                        Qt::IgnoreAspectRatio,
                        Qt::SmoothTransformation);;
}   // requestImage
UeTypeRoles UeOrdersModel::roleNames() const
{
    UeTypeRoles roles;
    const int iRoleUserId=UeOrdersModel::ueRoleUserId;
    const int iRoleUserName=UeOrdersModel::ueRoleUserName;
    const int iRolePlaceId=UeOrdersModel::ueRolePlaceId;
    const int iRolePlaceName=UeOrdersModel::ueRolePlaceName;
    const int iRoleProductId=UeOrdersModel::ueRoleProductId;
    const int iRoleProductImage=UeOrdersModel::ueRoleProductImage;
    const int iRoleProductName=UeOrdersModel::ueRoleProductName;
    const int iRoleProductPriceSell=UeOrdersModel::ueRoleProductPriceSell;
    const int iRoleProductVatRate=UeOrdersModel::ueRoleProductVatRate;
    const int iRoleProductQuantity=UeOrdersModel::ueRoleProductQuantity;
    const int iRoleOrderAmountWithoutVAT=UeOrdersModel::ueRoleOrderAmountWithoutVAT;
    const int iRoleOrderAmountWithVAT=UeOrdersModel::ueRoleOrderAmountWithVAT;
    roles.insert(iRoleUserId,
                 "ueRoleUserId");
    roles.insert(iRoleUserName,
                 "ueRoleUserName");
    roles.insert(iRolePlaceId,
                 "ueRolePlaceId");
    roles.insert(iRolePlaceName,
                 "ueRolePlaceName");
    roles.insert(iRoleProductId,
                 "ueRoleProductId");
    roles.insert(iRoleProductImage,
                 "ueRoleProductImage");
    roles.insert(iRoleProductName,
                 "ueRoleProductName");
    roles.insert(iRoleProductPriceSell,
                 "ueRoleProductPriceSell");
    roles.insert(iRoleProductVatRate,
                 "ueRoleProductVatRate");
    roles.insert(iRoleProductQuantity,
                 "ueRoleProductQuantity");
    roles.insert(iRoleOrderAmountWithoutVAT,
                 "ueRoleOrderAmountWithoutVAT");
    roles.insert(iRoleOrderAmountWithVAT,
                 "ueRoleOrderAmountWithVAT");
    return roles;
}   // roleNames
int UeOrdersModel::columnCount(const QModelIndex &parent) const
{
    Q_UNUSED(parent);
//    qDebug() << "UeOrdersModel::columnCount: " << this->record().count();
    return this->record().count();
}
int UeOrdersModel::rowCount(const QModelIndex &parent) const
{
    Q_UNUSED(parent);
//    qDebug() << "UeOrdersModel::rowCount: " << this->query().size();
    return this->query().size();
}   // rowCount
QVariantMap UeOrdersModel::get(int row)
{
    QHash<int,QByteArray> names=this->roleNames();
    QHashIterator<int, QByteArray> i(names);
    QVariantMap res;
    while (i.hasNext())
    {
        i.next();
        QModelIndex idx=this->index(row,
                                    0);
        QVariant data=idx.data(i.key());
        res[i.value()]=data;
    }   // while
    return res;
}   // get
void UeOrdersModel::ueConnectToDatabase(const QString& userId,
                                        const QString& placeId)
{
    if(!QSqlDatabase::connectionNames().contains(UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_ORDERS,
                                                 Qt::CaseInsensitive))
    {
        this->ueSetDatabase(QSqlDatabase::addDatabase(UePosDatabase::DATABASE_DRIVER,
                                                      UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_ORDERS));
    }   // if
    this->ueDatabase().setHostName(UePosDatabase::UeDatabaseConnectionParameters::DATABASE_HOSTNAME);
    this->ueDatabase().setDatabaseName(UePosDatabase::UeDatabaseConnectionParameters::DATABASE_NAME);
    this->ueDatabase().setUserName(UePosDatabase::UeDatabaseConnectionParameters::DATABASE_USERNAME);
    this->ueDatabase().setPassword(UePosDatabase::UeDatabaseConnectionParameters::DATABASE_PASSWORD);
    if(this->ueDatabase().open())
    {
        this->setQuery(UePosDatabase::UeSqlQueries::UeTableOrders::SQL_QUERY_GET_ORDERS_FILTERED_BY_USERID_PLACEID.arg(userId)
                                                                                                                  .arg(placeId),
                       this->ueDatabase());
        if(this->lastError().isValid())
        {
            emit this->ueSignalDatabaseConnectionChanged(UeDatabaseConnectionStatus::NOT_CONNECTED);
            qDebug() << this->lastError().text();
        }
        else
        {
            emit this->ueSignalDatabaseConnectionChanged(UeDatabaseConnectionStatus::CONNECTED);
        }   // if
    }
    else
    {
        emit this->ueSignalDatabaseConnectionChanged(UeDatabaseConnectionStatus::NOT_CONNECTED);
    }   // if
}   // ueConnectToDatabase
bool UeOrdersModel::ueAddOrder(const QString& userId,
                               const QString& placeId,
                               const QString& productId,
                               const QString& quantity)
{
    QSqlQuery queryInsertOrder(this->ueDatabase());
    bool result=false;
    queryInsertOrder.prepare(UePosDatabase::UeSqlQueries::UeTableOrders::SQL_QUERY_INSERT_NEW_RECORD);
    queryInsertOrder.addBindValue(userId);
    queryInsertOrder.addBindValue(placeId);
    queryInsertOrder.addBindValue(productId);
    queryInsertOrder.addBindValue(quantity.toUInt());
    if(queryInsertOrder.exec())
    {
        result=true;
    }
    else
    {
        if(queryInsertOrder.lastError().nativeErrorCode().compare(UePosDatabase::UeMySQLErrors::SQL_ERROR_RECORD_ALREADY_EXISTS)==0)
        {
            QSqlQuery queryIncreaseProductQuantity(this->ueDatabase());
            queryIncreaseProductQuantity.prepare(UePosDatabase::UeSqlQueries::UeTableOrders::SQL_QUERY_INCREASE_PRODUCT_QUANTITY.arg(userId)
                                                                                                                                .arg(placeId)
                                                                                                                                .arg(productId));
            if(queryIncreaseProductQuantity.exec())
            {
                result=true;
            }
            else
            {
                result=false;
            }   // if
        }   // if
    }   // if
    if(result==true)
    {
        this->setQuery(UePosDatabase::UeSqlQueries::UeTableOrders::SQL_QUERY_GET_ORDERS_FILTERED_BY_USERID_PLACEID.arg(userId)
                                                                                                                  .arg(placeId),
                       this->ueDatabase());
        if(this->lastError().isValid())
        {
            qDebug() << this->lastError().text();
        }   // if
    }   // if
    return result;
}   // ueAddOrder
void UeOrdersModel::ueSlotRefreshOrdersData(const QString& userId,
                                            const QString& placeId)
{
    this->ueSetUserId(userId);
    this->ueSetPlaceId(placeId);
    if(this->ueDatabase().isOpen())
    {
        this->setQuery(UePosDatabase::UeSqlQueries::UeTableOrders::SQL_QUERY_GET_ORDERS_FILTERED_BY_USERID_PLACEID.arg(userId)
                                                                                                                  .arg(placeId),
                       this->ueDatabase());
    }
    else
    {
        this->ueConnectToDatabase(userId,
                                  placeId);
    }   // if
    bool result=this->query().first();
    int i=0;
}   // ueSlotRefreshOrdersData
void UeOrdersModel::queryChange()
{
    qDebug() << "UeOrdersModel::queryChange(): " << this->query().lastQuery();
}   // queryChange

UeOrdersModel在main.cpp中实例化，它连接到数据库（就像我说的，检查了3x）：

UeOrdersModel* ueOrdersModel=new UeOrdersModel(qApp);

我在这个应用程序中有几个非常相似的型号，都运行得很完美，但这个没有。