选择查询返回“值:未定位在有效记录上"；在 Qt

问题描述

我一直在编写一个小代码，它应该用从 SQL 表中获取的值填充 QTableWidget 上的列.

I have been working on a small code which is supposed to fill up columns on a QTableWidget with values fetched from a SQL table.

这是一个小片段:

QString path = "C:\\ENTRIES.db";
QString itemToSearch = "ABC"; //This comes as a parameter to a slot actually, assigning it here for simplicity
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName(path);
db.open();

QSqlQuery query(db);
query.prepare("SELECT * FROM METADATA WHERE ITEM LIKE ':item %'");
query.bindValue(":item", itemToSearch);

if(query.exec())
{
    ui->tableWidgetSearchResults->setVisible(true);

    ui->tableWidgetSearchResults->clearContents();
    int rCount = ui->tableWidgetSearchResults->rowCount();

    while(query.next())
    {
        ui->tableWidgetSearchResults->setRowCount(rCount + 1);

        QTableWidgetItem *qtwParamName =  new QTableWidgetItem;
        qtwParamName->setFlags(qtwParamName->flags() & ~Qt::ItemIsSelectable & ~Qt::ItemIsEditable);
        qtwParamName->setText(query.value(0).toString());
        ui->tableWidgetSearchResults->setItem(rCount, 0, qtwParamName);

        QTableWidgetItem *qtwParamValue = new QTableWidgetItem;
        qtwParamValue->setFlags(qtwParamValue->flags() & ~Qt::ItemIsSelectable & ~Qt::ItemIsEditable);
        qtwParamValue->setText(query.value(1).toString());
        ui->tableWidgetSearchResults->setItem(rCount, 1, qtwParamValue);

        rCount++;
    }
}
else
{
     qDebug() << "Error message: " << query.lastError().text() ;
     ui->tableWidgetSearchResults->setHidden(true);
}
db.close();

当执行 query.value().toString()); 行时，应用程序输出打印:

When executing query.value(<index here>).toString()); lines, the Application Output prints:

QSqlQuery::value: not positioned on a valid record
QSqlQuery::value: not positioned on a valid record

我不确定我在这里遗漏了什么.

I'm not sure of what I am missing here.

注意:我使用的是 Qt 5.6、MSVC 2013 编译器和 SQLite 3.8.

Note: I am using Qt 5.6, MSVC 2013 compiler and SQLite 3.8.

推荐答案

@CL.谢谢你的提示.我试过这条线，它奏效了:

@CL. Thanks for the hint. I tried this line and it worked:

query.prepare("SELECT * FROM METADATA WHERE ITEM LIKE '" + itemToSearch + "%'");

显然 bindValue 在这种情况下是不合适的.

Apparently bindValue was inappropriate in this case.

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