ERROR: 'Variable does not exist

Question

I have a trigger bellow which calculates a sum of field in a related field in custom object . I am getting an error massage Variable does not exist:House_Improvements__c. Any ideas how can I resolve the issue? Thanks

trigger SumCalculations on House_Improvements__c (after insert,after update, after delete,after undelete) {
    List<id> PropertyIds = new List<id>();
    if(Trigger.isInsert || Trigger.isUndelete || Trigger.isupdate){
        For(House_Improvements__c himp1 : Trigger.new){
            PropertyIds.add(himp1.Property__c);
        }
    }
    if(Trigger.isDelete){
        For(House_Improvements__c  himp1 : Trigger.old){
            PropertyIds.add(himp1.Property__c);
        }
    }
    List<Property__c> PropertyToUpdate = new List<Property__c>();
    decimal sum = 0;
    if(Trigger.isInsert || Trigger.isUndelete || Trigger.isupdate){
        For (Property__c q: [SELECT id,SUM_Calculations__c, (SELECT id, Price__c FROM House_Improvements__r) FROM Property__c WHERE id =:PropertyIds]){
            sum = 0;
            for(House_Improvements__c   p : q.House_Improvements__r)
                sum = sum + p.House_Improvements__c ;
            q.SUM_Calculations__c  = sum;
            PropertyToUpdate .add(q);
        }
        try{
            update PropertyToUpdate ;
        }Catch(Exception e){
            System.debug('Exception :'+e.getMessage());
        }
    }
    if(Trigger.isDelete){
        For(Property__c q : [SELECT SUM_Calculations__c ,(SELECT id,Price__c FROM House_Improvements__r) FROM Property__c WHERE id =: PropertyIds]){
            sum = 0;
            for(House_Improvements__c  p : q.House_Improvements__r)
                sum = sum + p.House_Improvements__c ;
            q.SUM_Calculations__c  = sum;
           PropertyToUpdate .add(q);
        } 
        try{
            update PropertyToUpdate ;
        }Catch(Exception e){
            System.debug('Exception :'+e.getMessage());
        }
    }
}

Answer 1

You can't add a List<SObject> to a Decimal, so sum = sum + p.House_Improvements__c would fail even if you used the correct reference to the child list (House_Improvements__r).

Incorrect:

sum = sum + p.House_Improvements__c;

Correct

for (House_Improvements__c child : p.House_Improvements__r)
    sum += child.Price__c;

Please note, you should always use singular object names. Your code would be much less confusing if you had done so here. If it is not too late, rename your object to House_Improvement__c.