Question

我在QT-SQL中创建了一个有两个表的程序。感兴趣的领域是查看DDL - 数据定义语言部分。这是在createDb（）中。但是，为了编译，我已经更新了整个文件。我的目标是当更新表dttServiceList时，应更新dttEventList的Id。我在这里使用过级联。但是，我看到在dttServiceList中插入记录时，记录未插入dttEventList中。我在这里错过了什么？级联规则就在这里。我正在使用qt-sqlite。我也试过在这里添加触发器，但是我的sql浏览器挂了。

CREATE or REPLACE TRIGGER up1
AFTER INSERT ON dttServiceList
BEGIN
    INSERT INTO dttEventList  values (0,"action",1);
END;

另一部分是，那里的外键有什么意义，级联部分？

#include <QCoreApplication>
#include <QtSql>
#include <QtDebug>
#include <QDir>

const QString dbPathName = "/export/home/hello/demo.db";


class sqlExample
{
 public:
    sqlExample();
    void insertDemoData();
    void replaceDemoData();

  private:

    QSqlDatabase m_demo_db;
    void createDb();

};

sqlExample::sqlExample()
{
    createDb();

}

void sqlExample::replaceDemoData()
{
    /** associate db with query **/
    QSqlQuery query( m_demo_db );

    unsigned int chan = 555;
    unsigned int uqId = 32135;

    qDebug()<<__PRETTY_FUNCTION__;

    /** To ensure atomic operations - failure defensive **/
    QSqlDatabase::database().transaction();

    QString queryString = "update dttServiceList SET channelNum = " + QString::number(chan) + " where Id = " + QString::number(uqId);

    query.prepare(queryString);

    if ( query.exec() == false)
    {
        qDebug()<<"Query replaceDemoData Failed!!";
    }


    QSqlDatabase::database().commit();

}

void sqlExample::insertDemoData()
{
    /** associate db with query **/
    QSqlQuery query ( m_demo_db );

    qDebug()<<__PRETTY_FUNCTION__;

    qDebug()<<"Insert or replace Data here";

    /** To ensure atomic operations - failure defensive **/
    QSqlDatabase::database().transaction();

    for( int i= 100, j = 32131; i<= 120; i++,j++)
    {
        query.prepare("INSERT OR REPLACE INTO dttServiceList values (?, ?, ?)");
        query.bindValue(0, j);
        query.bindValue(2, i);
        query.bindValue(1, "Action");

        if ( query.exec() == false)
        {
            qDebug()<<"Query Insert or replace Failed!!";
        }
    }

    QSqlDatabase::database().commit();

    qDebug()<<"Insert or replace data exit";

}

void sqlExample::createDb()
{
#if 1
        QDir dir;
        qDebug()<<"Creating demo.db";

        /** create db here **/
        m_demo_db = QSqlDatabase::addDatabase("QSQLITE", dbPathName);
        m_demo_db.setConnectOptions("QSQLITE_BUSY_TIMEOUT=100000");
        m_demo_db.setDatabaseName(dbPathName);


        /** return 0 is error here **/

        if(! dir.exists(dbPathName) )
        {

                qDebug()<<"Start transaction demo.db";

                if(!m_demo_db.open())
                {
                        qDebug()<<"Error in opening demodb";
                }

                /** In DDL no transaction is required **/

                /** associate db with query **/
                QSqlQuery query ( m_demo_db );

                /** Create Table for storing user preference LCN for DTT **/

                qDebug()<<"Create Table postcode.db";
                query.prepare(" CREATE TABLE  dttServiceList (Id INTEGER PRIMARY KEY, attrib varchar(20), channelNum integer )" );

                if ( false == query.exec())
                {
                        qDebug()<<"Create dttServiceList table failed";
                }

                /** The Id in the dttEventList is the foreign key and is associated with the table dttServiceList attribute Id **/
                query.prepare(" CREATE TABLE  dttEventList (EventId INTEGER PRIMARY KEY, programName varchar(20), \
                               Id INTEGER, FOREIGN KEY(Id) REFERENCES dttServiceList(Id) ON UPDATE CASCADE )" );

                if ( false == query.exec())
                {
                    qDebug()<<"Create dttEventList table failed";
                }

                /** Do Indexing on ChannelId **/
                qDebug()<<"Create Indexing demo.db -dttEventList";
                query.prepare(" CREATE INDEX pEventId ON dttEventList (EventId)" );

                if ( false == query.exec())
                {
                        qDebug()<<"Indexing dttEventList failed";
                }

                /** Do Indexing on ChannelId **/
                qDebug()<<"Create Indexing demo.db";
                query.prepare(" CREATE INDEX pIndex ON dttServiceList (Id)" );

                if ( false == query.exec())
                {
                        qDebug()<<"Indexing dttServiceList failed";
                }

                /* Transaction complete **/
                  /** In DDL no transaction is required **/

        }

        else
        {
                qDebug()<<"Existing db..open!";

                if(!m_demo_db.open())
                {
                        qDebug()<<"Error in opening demoDb..already exists!";
                }
        }

#endif
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    sqlExample *p_sqlInstance = new sqlExample;

    p_sqlInstance->insertDemoData();

    p_sqlInstance->replaceDemoData();

    qDebug()<<"Sql Function Executed";

    delete p_sqlInstance;

    return a.exec();
}

Answer 1

ON UPDATE CASCADE仅适用于实际的UPDATE语句。（INSERT OR REPLACE是DELETE和INSERT的组合。）

没有级联INSERT的功能。如果要插入多个相关记录，则必须插入所有相关记录。

更新主表后，如何关联外键以更新辅助表的列？

1 个答案: