How to automatically copy fields from one Sobject to another - salesforce

Question

Im trying to create automation to copy Zipcode__c text field in connection sObject to Zip_code__c text field on Prem sObject. I can't use formula references since i need to be able to search copied field. One connection can have many Prems.
trigger updatePremFromConnection on Prem__c (before insert,after insert, after update,before update) {
List<Connection__c> connection = new List<Connection__c>();
for (Prem__c p: [SELECT Connection_id__c,id, Name
FROM Prem__c
WHERE Connection_id__c
NOT IN (SELECT id FROM Connection__c)
AND id IN : Trigger.new ]){
connection.add(new Connection__c(
ZipCode__c = p.Zip_Code__c));
}
if (connection.size() > 0) {
insert connection;
}
}
i need ZIp code field on the prem__c to be auto updated when i edit connection.

Answer 1

There are several issues with this code.
Trigger Object
Your trigger is on the wrong object and is doing exactly the opposite of your stated intent.
i need ZIp code field on the prem__c to be auto updated when i edit connection.
Your trigger on the Prem__c object attempts to copy data to the Connection__c object, while your objective is to copy from Prem__c to Connection__c. You'll definitely need an after update trigger on Connection__c and a before insert trigger on Prem__c; however, if the relationship between the two objects is Lookup or a Master-Detail relationship configured to be reparentable, you'll also need an update trigger on the child object Prem__c to handle situations where the child record is reparented, by updating from the new parent Connection.
Logic
This logic:
for (Prem__c p: [SELECT Connection_id__c,id, Name
FROM Prem__c
WHERE Connection_id__c
NOT IN (SELECT id FROM Connection__c)
AND id IN : Trigger.new ]){
connection.add(new Connection__c(
ZipCode__c = p.Zip_Code__c));
}
really doesn't make sense. It only finds Prem__c records in the trigger set that don't have an associated Connection, makes a new Connection, and then doesn't establish a relationship between the two records. The way that it does this is needlessly inefficient; that NOT IN subquery doesn't need to be there because it can simply by Connection_Id__c = null.
Instead, you probably want your Connection__c trigger to have a query like this:
SELECT ZipCode__c, (SELECT Zip_Code__c FROM Prems__r)
FROM Connection__c
WHERE Id IN :Trigger.new
Then, you can iterate over those Connection__c records with an inner for loop over their associated Prem__c records. Note that above you'll need to use the actual relationship name where I have Prems__r. The logic would look something like this:
for (Connection__c conn : queriedConnections) {
for (Prem__c prem : conn.Prems__r) {
if (prem.Zip_Code__c != conn.ZipCode__c) {
prem.Zip_Code__c = conn.ZipCode__c
premsToUpdate.add(prem);
}
}
}
update premsToUpdate;
Before running the query, you should also gather a Set<Id> of only those records for which the ZipCode__c field has actually changed, i.e., where thisConn.ZipCode__c != Trigger.oldMap.get(thisConn.Id).ZipCode__c. You'd use that Set<Id> in place of Trigger.new in your query, so that you only obtain those records with relevant changes.