Trigger to check if a file is attached to a custom object record

Question

I have a scenario where I need to check if a file has been added to a custom object record. If a file is already present, then the user should not be able to upload more files. Else, the user should be able to upload files.

Here is what I have tried.

trigger CheckFile on ContentDocumentLink (before insert) {
    List<ContentDocumentLink> cdls = ( Trigger.new == null ? Trigger.old : Trigger.new );
    
    Set<ID> parentIds = new Set<ID>();
    Set<ID> NotEligible = new Set<ID>();
    
    for (ContentDocumentLink cdl : cdls) {
        parentIds.add( cdl.LinkedEntityId );
    }
    

    List<Menu__c> menuIds = [SELECT Id FROM Menu__c WHERE Id IN :parentIds];
    
    
    for (Menu__c pk : menuIds){
            NotEligible.add(pk.id); 
                        } 
    
    System.debug(NotEligible);
    
    for (ContentDocumentLink cdls : Trigger.new) {
           if(NotEligible.contains(cdls.LinkedEntityId))
             cdls.addError('You cannot insert an image record.');
        }
    
 

}

I have a file associated with each record of a custom object. If the image file is there for the record, I do not want to be able to add more image files to it. Else, I want to be able to add a picture.

Answer 1

You are currently just querying all parent records. Those will always be there. You probably want to query for child records belonging to those parents. I.e. instead of

List<Menu__c> menuIds = [SELECT Id FROM Menu__c WHERE Id IN :parentIds];

You will want to do something like

List<ContentDocumentLink> existingCdlParentIds = [SELECT LinkedEntityId FROM ContentDocumentLink WHERE LinkedEntityId IN :parentIds];

This way you'll find all parentids with existing files.

Then change your loop to check through these existing ContentDocumentLinks and gather the parentid's (LinkedEntityID's)

//for (Menu__c pk : menuIds){
//        NotEligible.add(pk.id); 
//                    } 
//                    
for (ContentDocumentLink cdl : existingCdlParentIds){
    NotEligible.add(cdl.LinkedEntityId);
}

Then possibly add a filter for parent record type, if that is needed.

Answer 2

I finally got the solution to the problem.

trigger CheckFile on ContentDocumentLink (before insert) {
    List<ContentDocumentLink> cdls = ( Trigger.new == null ? Trigger.old : Trigger.new );
    
    Set<ID> parentIds = new Set<ID>();
    Set<ID> NotEligible = new Set<ID>();
    
    for (ContentDocumentLink cdl : cdls) {
        parentIds.add( cdl.LinkedEntityId );
    }
    
    List<ContentDocumentLink> refinedContentDocumentList = new List<ContentDocumentLink>();
    List<ContentDocumentLink> existingCdlParentIds = [SELECT LinkedEntityId FROM ContentDocumentLink WHERE LinkedEntityId IN :parentIds];
    
    for(ContentDocumentLink cdLink : existingCdlParentIds){
        if(String.valueOf(cdLink.LinkedEntityId.getSObjectType()) != 'User'){
            refinedContentDocumentList.add(cdLink);
        }
    }
    
    for (ContentDocumentLink cdl : refinedContentDocumentList){
    NotEligible.add(cdl.LinkedEntityId);
}
  
    
    for (ContentDocumentLink cdls : Trigger.new) {
           if(NotEligible.contains(cdls.LinkedEntityId))
             cdls.addError('You cannot insert an image record.');
        }
    
 

}