Sqlite connection weird thing

[jsulm]

@masa4 I repeat myself: Please add error handling: https://doc.qt.io/qt-6/qsqldatabase.html#lastError and https://doc.qt.io/qt-6/qsqlquery.html#lastError

[masa4]

@jsulm Thank you for advice. I added it like:

DB::DB(const QString &path)
{
    m_db = QSqlDatabase::addDatabase("QSQLITE");
    m_db.setDatabaseName(path);

    if(!m_db.open())
        qDebug() << "Error: connection with database failed";
    else
        qDebug() << "Database: connection ok";
    qDebug() << m_db.lastError().text();
}

When i used in this way and set the path's value to a wrong value it returns empty text. no error. and output is "Database: connection ok" but actually its not ok.

[jsulm]

@masa4 You wrote before: "my sql queries does not run". So, please add error handling in the code where you're executing SQL queries to see what exactly the problem is (https://doc.qt.io/qt-6/qsqlquery.html#lastError).

[Emre MUTLU]

maybe your quaries not work right cause your code work for me

[masa4]

@jsulm
one function in db.cpp:

double DB::selectData()
{
    QSqlQuery query;
    query.prepare("SELECT col1 FROM mytable");

    if(query.exec()){
        query.first();
        return query.value(0).toDouble();
    }
    else{
        query.lastError().text();
        return -1;
    }
}

mainwidget.h:

public:
DB *db = new DB;

mainwidget.cpp:

ui->labeldb->setText(QString::number(db->selectData()));

When path value is setted to like "mydbname" the return value -1 show up on my label. If i corrected path with absolute value like "/home/projectfolder/mydbname" i got right value on my label(its 10)
But still no error messages. Error messages show as empty text, like this: ""

[jsulm]

@masa4 said in Sqlite connection weird thing:

But still no error messages

Of course not - you are not printing the error message...

qDebug() << query.lastError().text();

[Emre MUTLU]

double DB::selectData()
{
    QSqlQuery query;
    query.prepare("SELECT col1 FROM mytable");

    if(query.exec()){
       while(query.first()) {
        return query.value(0).toDouble();
      }
    }
    else{
        qDebug()<<query.lastError();
        return -1;
    }
}

try this

[masa4]

@jsulm ow sorry didnt realize it. its:

"No query Unable to fetch row"

[masa4]

@Emre-MUTLU said in Sqlite connection weird thing:

if(query.exec()){
while(query.first()) {
return query.value(0).toDouble();
}
}

nope. same error. But actual problem is this code works when i use absolute path. But not for relative path.

[Emre MUTLU]

did you check db is open when you trying to using query

[Emre MUTLU]

double DB::selectData()
{
  if(db.open()) {
    QSqlQuery query;
    query.prepare("SELECT col1 FROM mytable");

    if(query.exec()){
       while(query.first()) {
        return query.value(0).toDouble();
      }
    } else{
        qDebug()<<query.lastError();
        return -1;
    }
}else {
qDebug()<<db.lastError();
}
}

something like this

[jsulm]

@Emre-MUTLU You should also check the return value of query.prepare("SELECT col1 FROM mytable");
Try also:

QSqlQuery query("SELECT col1 FROM mytable");

[Emre MUTLU]

@jsulm

double DB::selectData()
{
  if(db.open()) {
    QSqlQuery query("SELECT col1 FROM mytable");
    if(query.exec()){
       while(query.first()) {
        return query.value(0).toDouble();
      }
    } else{
        qDebug()<<query.lastError();
        return -1;
    }
}else {
qDebug()<<db.lastError();
}
}

[masa4]

@jsulm said in Sqlite connection weird thing:

isopen returns true. query.prepare() returns false.

[jsulm]

@Emre-MUTLU said in Sqlite connection weird thing:

double DB::selectData()
{
if(db.open()) {
QSqlQuery query("SELECT col1 FROM mytable");
if(query.exec()){
while(query.first()) {
return query.value(0).toDouble();
}
} else{
qDebug()<<query.lastError();
return -1;
}
}else {
qDebug()<<db.lastError();
}
}

You forgot to mention whether this version works...

[jsulm]

@masa4 said in Sqlite connection weird thing:

query.prepare() returns false.

Then print the error just after query.prepare()

[masa4]

@jsulm Same error. And i think there is nothing wrong with my sql queries. Because they work if i set dbname with absolute path.

[masa4]

@jsulm the error(i replaced mytable with my table name by the way):

"no such table: mytable Unable to execute statement"

[jsulm]

@masa4 said in Sqlite connection weird thing:

no such table: mytable Unable to execute statement

And does this table really exist? If a new SQLite database file is created there are no tables and you have to create them first.

[masa4]

@jsulm Yes of course this table exist. Also i can read from this table. But I have to provide full path of sqlite file to setDatabaseName method.

db.setDatabaseName("/home/projectfolder/mydbfile"); //Absolute path - Works without any problem
db.setDatabaseName("mydbfile"); //Relative path - Does not work

I got this errors when i use relative path. But i want to use relative path, database file is inside the project folder.