Trigger to restrict duplicate record for a particular type - salesforce

Question

I have a custom object consent and preferences which is child to account.
Requirement is to restrict duplicate record based on channel field.
foe example if i have created a consent of channel email it should throw error when i try to create second record with same email as channel.
The below is the code i have written,but it is letting me create only one record .for the second record irrespective of the channel its throwing me the error:
Trigger code:
set<string> newChannelSet = new set<string>();
set<string> dbChannelSet = new set<string>();
for(PE_ConsentPreferences__c newCon : trigger.new){
newChannelSet.add(newCon.PE_Channel__c);
}
for(PE_ConsentPreferences__c dbcon : [select id, PE_Channel__c from PE_ConsentPreferences__c where PE_Channel__c IN: newChannelSet]){
dbChannelSet.add(dbcon.PE_Channel__c);
}
for(PE_ConsentPreferences__c newConsent : trigger.new){
if(dbChannelSet.contains(newConsent.PE_Channel__c))
newConsent.addError('You are inserting Duplicate record');
}

Answer 1

Your trigger blocks you because you didn't filter by Account in the query. So it'll let you add 1 record of each channel type and that's all.
I recommend not doing it with code. It is going to get crazier than you think really fast.
You need to stop inserts. To do that you need to compare against values already in the database (fine) but also you should protect against mass loading with Data Loader for example. So you need to compare against other records in trigger.new. You can kind of simplify it if you move logic from before insert to after insert, you can then query everything from DB... But it's weak, it's a validation that should prevent save, it logically belongs in before. It'll waste account id, maybe some autonumbers... Not elegant.
On update you should handle update of Channel but also of Account Id (reparenting to another record!). Otherwise I'll create consent with acc1 and move it to acc2.
What about undelete scenario? I create 1 consent, delete it, create identical one and restore 1st one from Recycle Bin. If you didn't cover after undelete - boom, headshot.
Instead go with pure config route (or simple trigger), let the database handle that for you.
Make a helper text field, mark it unique.
Write a workflow / process builder / simple trigger (before insert, before update) that writes to this field combination of Account__c + ' ' + PE_Channel__c. Condition could be ISNEW() || ISCHANGED(Account__c) || ISCHANGED(PE_Channel__c)
Optionally prepare data fix to update existing records.
Job done, you can't break it now. And if you ever need to allow more combinations (3rd field) it's easy for admin to extend it. As long as you keep under 255 chars total.
Or (even better) there are duplicate matching rules ;) give them a go before you do anything custom? Maybe check https://trailhead.salesforce.com/en/content/learn/modules/sales_admin_duplicate_management out.