Execute Anonymous Error :- System.ListException: List index out of bounds: 0?

Question

While Updating the Custom Object(SiteContracts__c) fields through Execute Anonymous I am getting this Error. Here is my code:

List<SiteContracts__c> sitecontractList = new List<SiteContracts__c>();

  sitecontractList = [SELECT Id,X6L_Water__c,field1__c.field2__c(Select id,visit__r.visit_type__c,visit__c,X6L_Water_Qty__c,field1__c,field2__c,
                      Site_Contract__c,Service_Sheet_Type__c from Service_Sheets__r
                       WHERE Fire_Extinguisher_Service_complete__c=True ORDER BY createdDate DESC LIMIT 1) FROM SiteContracts__c];

Engineer_Checklist__c tempSS;
Boolean check;
if(sitecontractList.size()>0){
for(SiteContracts__c siteContract:sitecontractList) {
    tempSS=siteContract.Service_Sheets__r[0];
    check=false;
    if((tempSS.visit__r.Visit_Type__c=='Service Revisit FOC'|| tempSS.visit__r.Visit_Type__c=='Service Revisit') 
                                    && tempSS.Service_Sheet_Type__c=='Fire Extinguisher' )
    {
        check=true;
    }
         siteContract.X6L_Water__c=(check?(siteContract.X6L_Water__c==NULL?0:siteContract.X6L_Water__c)+(tempSS.X6L_Water_Qty__c==NULL?0:tempSS.X6L_Water_Qty__c):tempSS.X6L_Water_Qty__c);
             siteContract.X6L_Water__c=(siteContract.X6L_Water__c==0?tempSS.X6L_Water_Qty__c:siteContract.X6L_Water__c);

 siteContract.field1__c=(check?(siteContract.field1==NULL?0:siteContract.field1__c)+(tempSS.field1==NULL?0:tempSS.field1__c):tempSS.field1__c);
             siteContract.field1__c=(siteContract.field1__c==0?tempSS.field1:siteContract.field1__c);

 siteContract.field2__c=(check?(siteContract.field2__c==NULL?0:siteContract.field2__c)+(tempSS.field2__c==NULL?0:tempSS.field2__c):tempSS.field2__c);
             siteContract.field2__c=(siteContract.field2==0?tempSS.field2__c:siteContract.field2__c);
 }
  update sitecontractList;       
}

I Checked the Query in Query Editor and it retrieved the values. but I don know what is wrong in my code. Can anyone help me. Thanks in advance.

Answer 1

Judging from the errormessage, t must be occurring in this line:

tempSS=siteContract.Service_Sheets__r[0];

So the error means that for the particular siteContract that the code is looking at in that iteration, the Service_Sheets__r list is empty.

You'd need to check for that first:

if(!siteContract.Service_Sheets__r.isEmpty()){
   // do the actions
}   

Answer 2

I suspect the problem you're having is that when you run this query

sitecontractList = [SELECT Id,X6L_Water__c,field1__c.field2__c(Select id,visit__r.visit_type__c,visit__c,X6L_Water_Qty__c,field1__c,field2__c,
                      Site_Contract__c,Service_Sheet_Type__c from Service_Sheets__r
                       WHERE Fire_Extinguisher_Service_complete__c=True ORDER BY createdDate DESC LIMIT 1) FROM SiteContracts__c];

is that you're also running a subquery with a limit of 1. :

(Select id,visit__r.visit_type__c,visit__c,X6L_Water_Qty__c,field1__c,field2__c,
                          Site_Contract__c,Service_Sheet_Type__c from Service_Sheets__r
                           WHERE Fire_Extinguisher_Service_complete__c=True ORDER BY createdDate DESC LIMIT 1)

You may want to OrderBy createdDate and use some other field to see if record has previously been processed by trigger to exclude those records.

Based on the results of the inner subquery (limited to 1 result), you then do independent operations on Contract.X6L_Water__c, siteContract.field1__c and siteContract.field2__c that are all dependant on the subquery.

In reality, there may have been none or more than one result or of the subquery even though you only asked or one to be returned. That could cause siteContract.X6L_Water__c==0?, siteContract.field1__c==0? and siteContract.field2__c==NULL? to be mismatched or incorrect depending on which subquery has been previously returned as the trigger fires. If none were returned, that would definitely cause your list to be out of bounds. If more than one is returned, based on the logic your trigger is using, I'd see no problem with processing them all at once.