Is there a better way for handling exceptions ? Can I do the same thing but only with one try catch ?
Do I need to create my own exceptions class ?
try { firstname = bd["firstname"].ToString(); } catch (KeyNotFoundException fe) { firstname = null; } try { lastname = bd["lastname"].ToString(); } catch (KeyNotFoundException fe) { lastname = null; } try { phone = bd["phone"].ToString(); } catch (KeyNotFoundException fe) { phone = null; } ... ... Do not use exceptions for normal program flow if possible:
firstname = bd.ContainsKey("firstname") ? bd["firstname"] : null; lastname = bd.ContainsKey("lastname") ? bd["lastname"] : null; phone = bd.ContainsKey("phone") ? bd["phone"] : null; or (assuming you are accessing a Dictionary):
bd.TryGetValue("firstname", out firstname); bd.TryGetValue("lastname", out lastname); bd.TryGetValue("phone", out phone); 
bd is a BsonDocument you could replace ContainsKey with Contains.
Contains if you want to know if the dictionary contains the given key(so like ContainsKey). So TryGetValue seems to be equivalent to Dictionary.TryGetValue.firstname = Convert.ToString( bd["firstname"]);
lastname = Convert.ToString( bd["lastname"]);
phone = Convert.ToString(bd["phone"]);
Try Convert.ToString("string Value") method instend of .ToString() to avoid Exception.
If you want to use try catch blocks with minimum overhead, You can write all the code in one try block and write multiple catch blocks.
try { firstname = bd["firstname"].ToString(); lastname = bd["lastname"].ToString(); phone = bd["phone"].ToString(); } catch (KeyNotFoundException fe) { firstname = null; } catch (KeyNotFoundException ex) { lastname = null; } catch (KeyNotFoundException xe) { phone = null; } 
catch blocks will not work: only the first will be run.