code: public OSchemaHelper oDocument(String pkField, Object pkValue)
  	{
  		checkOClass();
  		List<ODocument> docs = db.query(new OSQLSynchQuery<ODocument>("select from "+lastClass.getName()+" where "+pkField+" = ?", 1), pkValue);
  		if(docs!=null && !docs.isEmpty())
  		{
  			lastDocument = docs.get(0);
  		}
  		else
  		{
  			lastDocument = new ODocument(lastClass);
  			lastDocument.field(pkField, pkValue);
  		}
  		return this;
  	}
docs: Create an {@link ODocument} if required of an current class.
  Existance of an document checked by specified primary key field name and required value
  @param pkField primary key field name
  @param pkValue required primary key value
  @return this helper