What is the problem in QSqlQuery?

_compiler

class QueryBuilder
{
public:
    QueryBuilder();
    QSqlQuery insert(const QString &query)
    {
        QSqlQuery qry;
        qry.prepare(query);
        
        return qry;
    }
}

#include "querybuilder.h"

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

    QueryBuilder b;
    b.insert("bla bla ...");  // ---> Output : QSqlQuery::prepare: database not open

    return a.exec();
}

can you help ?

mrjj

hi
Well, it wants a database open first :)
You seems not to have any?

http://stackoverflow.com/questions/7669987/what-is-the-correct-way-of-qsqldatabase-qsqlquery

_compiler

@mrjj I do not need connection now. this is just a class. Does this class can not be used without connecting?

raven-worx

@_compiler
as the Qt docs for QSqlQuery class say:

Warning: You must load the SQL driver and open the connection before a QSqlQuery is created. Also, the connection must remain open while the query exists; otherwise, the behavior of QSqlQuery is undefined.

mrjj

@_compiler said:
Well your class can , but when you do

qry.prepare(query);

it wants to talk to DB to check stuff.

_compiler

real class ...

class QueryBuilder
{
public:
    QueryBuilder();

    QSqlQuery insert(const QString &tableName, QMap<QString,QVariant>/*name,value*/ &values)
    {
            QSqlQuery qry;

            QString str = "INSERT INTO " + tableName +" (";
            QString val = "VALUES(";

            QMapIterator<QString, QVariant> it(values);
            while (it.hasNext()) {
                it.next();

                str += it.key();
                val += ":" + it.key();

                if(it.hasNext())
                {
                    str += ", ";
                    val += ", ";
                }else
                {
                    str += ") ";
                    val += ") ";
                }
            }

            str += val;

            qry.prepare(str);

            ///...

            return qry;
    }
}

mrjj

@_compiler
ok, but prepare need open database.

_compiler

@mrjj i got it . How else can I do ?

mrjj

well just wait until later to call qry.prepare(str); ?
The rest of the code just create the string.

but please notice what @raven-worx says. !

So maybe you should rethink the design of QueryBuilder to not use
QSqlQuery before a database is created and open.

what is the role of QueryBuilder ?

_compiler

@mrjj QueryBuilder class set of query.

for example ;

QueryBuilder b;

QSqlQuery q1, q2, q3, q4;

q1 = b.insert("bla bla ...");
q2 = b.update("bla bla ...");
q3 = b.remove("bla bla ...");
q4 = b.select("bla bla ...");

SqlWorkerThread *thread = new SqlWorkerThread(0);

//signal slot definitions ....

thread.addQuery(q1);
thread.addQuery(q2);
thread.addQuery(q3);
thread.addQuery(q4);

thread.start();

mrjj

@_compiler

Ok, i see, its a helper class.

Well you need to open a db then.

You dont need to do it in QueryBuilder.

If you open a db in main , QSqlQuery
will use this DB. You dont need pointer or reference.
Its handled internally.