How to efficiently use try catch blocks in PHP

Question

I have been using try  catch blocks in my PHP code  but I m not sure if I ve been using them correctly   For example  some of my code looks like    try          tableAresults    dbHandler- gt doSomethingWithTableA           tableBresults    dbHandler- gt doSomethingElseWithTableB       catch  Exception  e          return  e       So I m grouping multiple database operations in the same try catch block because if any exception occurs in any of the transaction  I will be able to handle it   I m doing it that way because I think that it s more readable and efficient than    try           tableAresults    dbHandler- gt doSomethingWithTableA       catch  Exception  e           return  e      try           tableBresults    dbHandler- gt doSomethingWithTableB       catch  Exception  e           return  e       Although  I m not sure if what I m doing is a good practice or just a lazy way to catch exceptions   My assumption is that only if an exception requires special handling  it should have its own try catch block  otherwise grouping them in the same try catch should be ok    So my question s  are   Is there any advantage of using try catch blocks per database transaction  or can I still group multiple database transactions in the same try catch block with no problem at all   Is it ok to nest try catch blocks  Thanks   EDIT  The return statement was primarily for demonstration purposes only  but I m also using returns in catch   because I m making an AJAX request to that method  and Javascript is expecting a JSON object  then if an exception occurs I return an empty JSON encoded array  I just thought that It wouldn t add any value to put specific code in my example

User · Accepted Answer

Important note  The following discussion assumes that we are talking about code structured as in the example above  no matter which alternative is chosen  an exception will cause the method to logically stop doing whatever it was in the middle of     As long as you intend to do the same thing no matter which statement in the try block throws an exception  then it s certainly better to use a single try catch  For example   function createCar         try         install engine          install brakes          catch  Exception  e            die  I could not create a car              Multiple try catch blocks are useful if you can and intend to handle the failure in a manner specific to what exactly caused it   function makeCocktail         try           pour ingredients            stir          catch  Exception  e            die  I could not make you a cocktail               try           put decorative umbrella          catch  Exception  e            echo  We  re out of umbrellas  but the drink itself is fine

User · Answer

When an exception is thrown  execution is immediately halted and continues at the catch   block  This means that  if you place the database calls in the same try   block and  tableAresults    dbHandler- gt doSomethingWithTableA    throws an exception   tableBresults    dbHandler- gt doSomethingElseWithTableB    will not occur  With your second option   tableBresults    dbHandler- gt doSomethingElseWithTableB    will still occur since it is after the catch   block  when execution has resumed    There is no ideal option for every situation  if you want the second operation to continue regardless  then you must use two blocks  If it is acceptable  or desirable  to have the second operation not occur  then you should use only one

User · Answer

For posterity sake the answer maybe too late You should check for the return value of the variable and throw an exception  In that case you are assured that the program will jump from where the exception is being raised to the catch block  Find below   try      tableAresults    dbHandler- gt doSomethingWithTableA       if   tableAresults        throw new Exception  Problem with tableAresults        tableBresults    dbHandler- gt doSomethingElseWithTableB       if   tableBresults        throw new Exception  Problem with tableBresults      catch  Exception  e        echo  e- gt getMessage

User · Answer

There is no reason against using a single block for multiple operations  since any thrown exception will prevent the execution of further operations after the failed one  At least as long as you can conclude which operation failed from the exception caught  That is as long as it is fine if some operations are not processed    However I d say that returning the exception makes only limited sense  A return value of a function should be the expected result of some action  not the exception  If you need to react on the exception in the calling scope then either do not catch the exception here inside your function  but in the calling scope or re-throw the exception for later processing after having done some debug logging and the like

User · Answer

in a single try catch block you can do all the thing the best practice is to catch the error in different catch block if you want them to show with their own message for particular errors

User · Answer

try        tableAresults    dbHandler- gt doSomethingWithTableA        if  tableAresults                throw new Exception  Problem with tableAresults               tableBresults    dbHandler- gt doSomethingElseWithTableB        if  tableBresults                 throw new Exception  Problem with tableBresults            catch  Exception  e        echo  e- gt getMessage

User · Answer

It s more readable a single try catch block  If its important identify a kind of error I recommend customize your Exceptions   try      tableAresults    dbHandler- gt doSomethingWithTableA       tableBresults    dbHandler- gt doSomethingElseWithTableB      catch  TableAException  e     throw  e    catch  Exception  e      throw  e

User · Answer

There is no any problem to write multiple lines of execution withing a single try catch block like below try  install engine    install break      catch Exception  e   show exception  e- gt getMessage        The moment any execption occure either in install engine or install break function the control will be passed to catch function  One more recommendation is to eat your exception properly  Which means instead of writing die  Message   it is always advisable to have exception process properly  You may think of using die   function in error handling but not in exception handling  When you should use multiple try catch block You can think about multiple try catch block if you want the different code block exception to display different type of exception or you are trying to throw any exception from your catch block like below  try      install engine        install break              catch Exception  e       show exception  e- gt getMessage           try  install body    paint body    install interiour      catch Exception  e   throw new exception  Body Makeover faield

[php] How to efficiently use try...catch blocks in PHP

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