Hi all, second post here - and I have been toiling away at this all day!! Would very much appreciate some help as I can't seem to find the similar issue in the forum and a solution that I can extrapolate to this scenario.

Error message from log/status in Dev Console:

Insert failed: First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, trigger_name: execution of BeforeInsert caused by: System.typeException: Invalid integer: expr0

Bit of background, I am writing my first apex trigger to generate a total (sum) in a field on the Account which sums the total amount for related contracts, that will eventually fit within certain criteria (I haven't added this part yet as I just want the basics working first!).

I know the problem is with my map, aggregateResult/SOQL.  I somehow had it working last night, but I didn't backup & obviously didn't stop to think what I had before I started playing with it!  Originally I had the map populate when it is declared (this isn't is but i remember vaugley it was all inline - something along the lines of):

map<ID, integer> cMap_THISFY = new map<ID, integer>(AggregateResult c: [SELECT AccountID, SUM(Invoice_Amount__c) FROM Contract WHERE AccountID IN :BookingAcctIDs GROUP BY AccountID]);

So after tinkering and realising I didn't know where/how all the bolts go back - but it doesn't run!  I had/having all sorts of trouble with the SOQL -> cMap_THISFY - first shot at rebuilding it was:

    	map<ID, integer> cMap_THISFY = new map<ID, integer>();
        for (AggregateResult c: [SELECT AccountID, SUM(Invoice_Amount__c)total
                                 FROM Contract 
                                 WHERE AccountID IN :BookingAcctIDs
                                 GROUP BY AccountID])
        	cMap_THISFY.put(c.get('AccountId'), c.get('expr0'));

 But this resulted in a compile error: 'Incompatiable key type Object for MAP<Id,Integer> - which I assume is due to AggregateResult being an object datatype

I finally got it to compile - this is the full set of the code I have at the moment:

/* Trigger to total up the related bookings linked to an account and get a 'total' 
   booking signed amount, when a record is inserted/updated/undeleted/deleted

   Written by: Adam Gill 
   Date: 01/11/2012
   (c) The Gap Partnership
   
*/   

trigger tr_updateBookingSigned on Contract (before insert, before update, after undelete, before delete) {

    //Create new list & map to store Account ID fields & the aggregateresult of SOQL
    set<ID> BookingAcctIDs = new set<ID>();  
	
    //Generate list of Account IDs, for accounts that need to be updated, based on type of trigger
    if (trigger.isDelete){
		for (Contract c : trigger.old){
       		BookingAcctIDs.add(c.AccountID);
      	}
    }
    else {
        for (Contract c : trigger.new){
            BookingAcctIDs.add(c.AccountID);
        }
	}
    
    
    //If Account IDs have been added successfully to list, process required calculations
    if (BookingAcctIDs.size() > 0) {

        system.debug('~~~~ CREATING MAP ~~~~');
    	
        //Create new map to store Account ID & sum amount fields 
    	map<ID, integer> cMap_THISFY = new map<ID, integer>();
        for (AggregateResult c: [SELECT AccountID, SUM(Invoice_Amount__c)total
                                 FROM Contract 
                                 WHERE AccountID IN :BookingAcctIDs
                                 GROUP BY AccountID]){
			ID aID = id.valueof('AccountID');
            integer aSUM = integer.valueof('expr0');
            system.debug('*** ' + aID + ' / ' + aSUM + ' ***');
        	cMap_THISFY.put(aID, aSUM);
        }
    	
        //Create new list to generate list of 'AccountsToUpdate'
    	list<Account> AccountsToUpdate = new list<Account>();
    	
        //From set of accounts IDs, retrieve ID & Bookings_Signed_This_FY field & assign sum from ContractMap.
    	for (Account acct : [SELECT Id, Bookings_Signed_This_FY__c
                             FROM Account
                             WHERE Id IN :BookingAcctIDs]){
//				double dblBookingsSignedThisFY = cMap_THISFY.get(acct.Id);
//          	acct.Bookings_Signed_This_FY__c = dblBookingsSignedThisFY;
            acct.Bookings_Signed_This_FY__c = cMap_THISFY.get(acct.Id);
           	AccountsToUpdate.add(acct);
      	}
    	
        //Update list of accounts with totalled data.
    	update AccountsToUpdate;
    }
}

 I feel like all I am doing is moving side ways, not actually understanding what the problem is... I have looked at a number of blogs but they seem to have been coded in previous versions of the API too: here is one of the blogs I was using to disect and try and learn while reverse engineering the solution I needed.  I orginally started out using the similar map methods but I couldn't get it to complie.  And I have tried to peice together the related examples in the developer blog for aggregateresults, bulk soql queries and maps - but I think I have sent too long looking at it and I can't make heads or tails of it anymore.

So with that code above I have it compling and I am using the Execute section of the dev console to create a mini-test which is very basic, but this all I had when I had the script above working, and I haven't updated any permissions in the Dev Sandbox over the last few days (trying to isolate permissions/FLS):

Contract c1 = new Contract();
c1.AccountId = '001R000000kxmFf';
c1.Delivery__c = 'a0IR0000002e7cN';
c1.Key_Booking_Contact__c = '003R000000ihmt5';
c1.Invoice_Amount__c = 50000;
c1.name = 'Test booking:' + string.valueof(datetime.now());
c1.StartDate = date.today();

insert c1;

I am pretty sure I am missing something quite simple - but as APEX syntax is a little different from VBA/etc that I have developed with until now, any guidance or assistance would be greatly appreciated - as I am about to start pulling out my hair!! :-)