Question

当我从comboBox中选择图书ID时，我想将图书名称的值加载到文本框中。首先，我编写了用于将Book Ids从数据库加载到comboBox的代码，并且它完全加载了。这是方法。

void FictionSection::loadComboVal()
{
    DatabaseConnection mydb;
    QSqlQueryModel *modl = new QSqlQueryModel();
  dbConOpen();

    QSqlQuery *query = new QSqlQuery(mydb.db) ;
    query->prepare(" select material_id from fiction ");
  bool flag = query->exec();

  //assigning the values to a QTableView
  if(flag == true)
  {
      modl->setQuery(*query);
      ui->cmbxId->setModel(modl);

}
  mydb.dbConClose();
}

然后，一旦从textBox中选择了书籍ID，我就编写了将值分配给comboBox的代码。这是代码段：

// loading book names once user select the book id from combo box
void FictionSection::on_cmbxId_currentIndexChanged(int index)
{
    QString value = ui->cmbxId->currentText();
    int id;
    if(!value.isEmpty())
    {
     id = value.toInt();
    }
//Loading book table values to a table

dbC    onOpen();
       QSqlQuery query  ;
       QString ids = QString("values('") + QString::number(id);
       query.prepare(" select material_title from book where material_id = '"+ids+"'");
     bool flag = query.exec();

     //assigning the values to a QTableView
     if(flag == true)
     {
        ui->lneditFicNme->setText(query.value(1).toString());


     }
    dbConClose();

}

但是后来加载到comboBox的值是不可见的，我无法像我预期的那样获得文本框的任何值。但没有编译或运行时错误。 Book Id在数据库中以int {book}的形式存储为varchar。

我更改了代码如下：

void FictionSection::on_cmbxId_currentIndexChanged(int index)
{
    QString value = ui->cmbxId->currentText();
    int id;
    if(!value.isEmpty())
    {
     id = value.toInt();
    }
//Loading book table values to a table

       dbConOpen();
       QSqlQuery query  ;
      // QString ids = QString("values('") + QString::number(id);
       query.prepare(" select material_title from book where material_id = ?");
       query.bindValue(0,id);
     bool flag = query.exec();

     //assigning the values to a QTableView
     if(flag == true)
     {
        ui->lneditFicNme->setText(query.value(1).toString());


     }
     else
     {

         QMessageBox :: critical(this,"Error",query.lastError().text());
     }
    dbConClose();

}

然后它给出如下错误：

QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.
QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.
QSqlQuery::value: not positioned on a valid record
QSqlQuery::value: not positioned on a valid record

我编辑了上面的代码，但仍然无法得到预期的结果。

void FictionSection::on_cmbxId_currentIndexChanged(int index)
{
    DatabaseConnection con;
     con.dbConOpen();


    QString value = ui->cmbxId->currentText();
    int id;
    if(!value.isEmpty())
    {
     id = value.toInt();
    }
//Loading book table values to a table


       QSqlQuery query  ;

      // QString ids = QString("values('") + QString::number(id);
       query.prepare(" select material_title from book where material_id = :id");
       query.bindValue(":id",id);
     bool flag = query.exec();

     //assigning the values to a QTableView
     if(flag == true)
     {

          while(query.next())
          {

             ui->lneditFicNme->setText(query.value(1).toString());

          }
     }
     else
     {

         QMessageBox :: critical(this,"Error",query.lastError().text());
     }
    con.dbConClose();
}

请帮我解决这个问题。提前谢谢

Answer 1

尝试使用QSqlQuery::next()方法定位有效记录。

将Qline编辑链接到qt c ++

1 个答案: