IMO, the problem isn't in Q_OBJECT (as long as AutochargeData does not use "Qt extras" - it is not an UI object, it declares no properties, slots or signals, etc.) The setOrderID() method is innocent. IMO, the problem is somewhere in the database. For starters, I recommend splitting the setOrderID() statement and seeing whether you pass and what values will the debugger show. Therefore:
Qt Code: 
  1. QVariant val = query.value("increment_id");   // does it pass?
  2. QString  str = val.toString();                // does it pass? What is in str?
  3.  
  4. setOrderID(str);                              // does it pass? What happens?
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Pleas, post your findings.