Been amending a piece of code on here to suit my needs but it won't compile. My naieve eyes cannot see the error of my ways:

trigger doRollup on Time_Record__c (after insert, after update, after delete, after undelete) {

  // List of parent record ids to update
    Set<Id> parentIds = new Set<Id>();
  
  // In-memory copy of parent records
  Map<Id,Time_Record__c> parentRecords = new Map<Id,Time_Record__c>();
  
  // Gather the list of ID values to query on
  for(Daily_Time_Record__c c:Trigger.isDelete?Trigger.old:Trigger.new)
    parentIds.add(c.Time_Record_Link__c);
    
  // Avoid null ID values
  parentIds.remove(null);
  
  // Create in-memory copy of parents
  for(Id parentId:parentIds)
    parentRecords.put(parentId,new Time_Record__c(Id=parentId,RollupTarget__c=0));
    
  // Query all children for all parents, update Rollup Field value
  for(Daily_Time_Record__c c:[select id,FieldToRoll__c,Time_Record_Link__c from Daily_Time_Record__c where id in :parentIds])
    parentRecords.get(c.Time_Record_Link__c).RollupTarget__c += c.FieldToRoll__c;
    
  // Commit changes to the database
  
  Database.update(parentRecords.values());
}

Where:

Time_Record__c is my parent

RollUpTarget__c is the place I am trying to roll to

Daily_Time_Record__c is the child

Time_Record_Link__c is the link to parent that exists on the child

FieldToRoll__c is a test field to roll up on the child

I *think* that is what I had to replace from this generic template:

trigger doRollup on Child__c (after insert, after update, after delete, after undelete) {
  // List of parent record ids to update
  Set<Id> parentIds = new Set<Id>();
  // In-memory copy of parent records
  Map<Id,Parent__c> parentRecords = new Map<Id,Parent__c>();
  // Gather the list of ID values to query on
  for(Child__c c:Trigger.isDelete?Trigger.old:Trigger.new)
    parentIds.add(c.ParentField__c);
  // Avoid null ID values
  parentIds.remove(null);
  // Create in-memory copy of parents
  for(Id parentId:parentIds)
    parentRecords.put(parentId,new Parent__c(Id=parentId,RollupField__c=0));
  // Query all children for all parents, update Rollup Field value
  for(Child__c c:[select id,Amount__c,ParentField__c from Child__c where id in :parentIds])
    parentRecords.get(c.ParentField__c).RollupField__c += c.Amount__c;
  // Commit changes to the database
  Database.update(parentRecords.values());
}

 Ideally I want to roll up a sum of 7 fields from the child (hence needing this solution), but starting small.