Sqlite connection weird thing

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.

jsulm

@masa4 said in Sqlite connection weird thing:

db.setDatabaseName("mydbfile"); //Relative path - Does not work

Are you aware that mydbfile is not the same as /home/projectfolder/mydbfile?
The first one is inside current working directory, which is most probably not /home/projectfolder (so you're creating a new file).

masa4

@jsulm Ow, now i see the point. The db inside the code folder, but current working folder name is actually build-project-desktop-debug. Yeah now issue clarified.