exceptions.md

Exception Handling

• Standard exception handling syntax - Order from Specific to Generic

try {
} catch(DmlException e) {
	// DmlException handling code here.
} catch(Exception e) {
	// Generic exception handling code here.
} finally {
	// Final code goes here
}

• Common Exception methods

  • getCause: Returns the cause of the exception as an exception object.
  • getLineNumber: Returns the line number from where the exception was thrown.
  • getMessage: Returns the error message that displays for the user.
  • getStackTraceString: Returns the stack trace as a string.
  • getTypeName: Returns the type of exception, such as DmlException, ListException, MathException, and so on.
  • Some exceptions such as DML exceptions have special methods
    • getDmlFieldNames - Returns the names of the fields that caused the error for the specified failed record.
    • getDmlId: Returns the ID of the failed record that caused the error for the specified failed record.
    • getDmlMessage: Returns the error message for the specified failed record.
    • getNumDml: Returns the number of failed records.

• Famous DML Exceptions

  • DmlException - Problems with DML Statements
  • ListException - Any problem with a list such as index out of bounds exceptions
  • NullPointerException - Problems with dereferencing a null variable.
  • QueryException - Any problem with SOQL queries, such as assigning a query that returns no records or more than one record to a singleton sObject variable.
  • SObjectException - Any problem with sObject records, such as attempting to change a field in an update statement that can only be changed during insert.

• To create a custom exception use

	public class MyException extends Exception {}
    
    // To create an exception
    new MyException();
    
    new MyException('This is bad'); // Error Message input
    
    new MyException(e); // Exception argument
    
    new MyException('This is bad', e); 
    // The first is the message and the second is the cause.