QSqlQuery not working

[BrainStorm]

I'm stucked at this problem since a very long time ( about one day or more ), I just can't find what's wrong! it looks so simple and until now everything in the project did work fine, relational tables, and etc, well, I isolated it in a function, may I explain first, I've loaded a QComboBox with a QSqlQueryModel with this query: "SELECT name FROM Categories", ok. Then I need to insert the id of the selected item in another table (for using as relation), I made this function:

int ProductsForm::categoryIdByName(const QString& name)
{
    QSqlQuery categories = QSqlQuery(model->database());
    categories.prepare("SELECT id FROM Categories "
               "WHERE name=:name)");
    categories.bindValue(":name",name);
    categories.exec();
    if(categories.size()==-1)
    {
    qDebug() << "error";
    return 1;
    }
    return cate

int ProductsForm::categoryIdByName(const QString& name)
{
    QSqlQuery categories = QSqlQuery(model->database());
    categories.prepare("SELECT id FROM Categories "
               "WHERE name=:name)");
    categories.bindValue(":name",name);
    categories.exec();
    if(categories.size()==-1)
    {
    qDebug() << "error";
    return 1;
    }
    return cate

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I call it with QComboBox::currentText(), BUT, as you see my concern there, query size aways return -1, no item! i've tried a lot of other querys, like "SELECT * FROM Categories", but nothing! I'm SURE the database, tables and items where created and inserted respectively, the program did work fine until this, I hope you guys can enlight-me and help me kick off this meaningless error. thanks in advance, sorry my bad english.