pretty simple question that I just can't figure. The first snippet updates a record just fine, but the second snippet does nothing, even though it compiles just fine. Many thanks.
Why does this work:
for(Pet__c P : PetList]){
if(P.Type__c == 'Cat'){
P.Age__c = 4;}
But this does not?
for(Pet__c P :[SELECT ID,
Type__c,
Age__c,
FROM Pet__c
WHERE ID IN :PetList]){
if(P.Type__c == 'Cat'){
P.Age__c = 4;}
PetList would have been aliased from Trigger.new in the first case, but in the second, it is a record from the database, a separate record in memory. The equivalent code would look something like:
for(Pet__c P :[SELECT ID,
Type__c,
Age__c,
FROM Pet__c
WHERE ID IN :PetList]){
if(P.Type__c == 'Cat'){
Trigger.newMap.get(p.id).Age__c = 4;
}
}
If you want to save data without a DML operation in a trigger class or trigger helper class, you must modify Trigger.new.
In the first code snippet, PetList has been assigned the Trigger.new which means it's is referencing the Trigger.new and in the before trigger context, Salesforce allows you to modify field values on the fly in Before context.
In the second code snippet you are querying records explicitly so you will have to call Update statement to perform an update.
From the documentation
Trigger.new - Returns a list of the new versions of the sObject records. This sObject list is only available in insert, update, and undelete triggers, and the records can only be modified in before triggers.
If you are performing a query then you will have to update those records explictly but that's not a good practice in Before context. Here is the doc reference which has explained everything you want to know. Context Variable Considerations
