Question

我有一个以Id作为主键的主表。还有另一个表，其中一个字段是外键 - “Id”，它指的是主表的主键“Id”。但是，当我从主表中删除Id时，不会从辅助表中删除Id。我有“ON DELETE CASCADE”。这是代码 -

要看的重要部分是以下内容 -

createDb - 所有DDL都在这里
sqlExample :: insertDemoData（） - ＆gt;它在主表和辅助表上插入数据。
sqlExample :: replaceDemoData（） - ＆gt;这是我希望在主表上删除的Id也应该导致从辅助表中删除的地方（记住，我在这里关联了一个外键。）

我已经在QT编写了这个程序。我正在使用sqlite数据库引擎。这是整个计划。我是Sql的新手，我很高兴，如果有人能给我一些解决方案，比如 - 1.基于级联。 2.基于触发器。解释，为什么现在不工作？

感谢您的回复。

#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 = 32151;

    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);

    QString queryString = "DELETE FROM dttServiceList 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 dttServiceList Failed!!";
        }

       query.prepare("INSERT OR REPLACE INTO dttEventList values (?, ? , ?)");
       query.bindValue(0, 5);
       query.bindValue(1, "Jackie-Cheng");
       /** foreign key **/
       query.bindValue(2, j);

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

为什么在级联上删除不能在下表中工作--sql？

0 个答案: