Query ContentDocumentLink in a batch gives Internal Salesforce.com Error

Question

I have a batch where I first query some ContentDocumentLink. If the query has some results, I got an internal Salesforce.com Error when the batch start during the SerialBatchApexRangeChunkHandler operation. Here is the code :

global class BATCH_ContentDocumentLink implements Database.Batchable < sObject > {

    String query;

    global BATCH_ContentDocumentLink() {
        query = 'SELECT ContentDocumentId FROM ContentDocumentLink ' +
            'WHERE LinkedEntityId IN (SELECT Id FROM User)';

    }


    global Database.QueryLocator start(Database.BatchableContext BC) {
        return Database.getQueryLocator(query);
    }

    global void execute(Database.BatchableContext BC, List < sObject > scope) {
        System.debug(scope);
    }

    global void finish(Database.BatchableContext BC) {

    }
}

What is the issue ?

Answer 1

I am not sure why it does not work with Database.QueryLocator but it works with custom iterables. It might be related to query restrictions that David Reed mentioned in comments.

(I copied iterator from this link: https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_iterable.htm)

Iterator:

global class CustomIterable 
   implements Iterator<ContentDocumentLink>{ 

   List<ContentDocumentLink> cdls {get; set;} 
   Integer i {get; set;} 

   public CustomIterable(){ 
       cdls =  [SELECT ContentDocumentId FROM ContentDocumentLink WHERE LinkedEntityId IN (SELECT Id FROM User)]; 
       i = 0; 
   }   

   global boolean hasNext(){ 
       if(i >= cdls.size()) {
           return false; 
       } else {
           return true; 
       }
   }    

   global ContentDocumentLink next(){ 
       // 8 is an arbitrary 
       // constant in this example
       // that represents the 
       // maximum size of the list.
       if(i == 8){return null;} 
       i++; 
       return cdls[i-1]; 
   } 
}

Iterable:

global class CustomIterableExample implements iterable<ContentDocumentLink>{
   global Iterator<ContentDocumentLink> Iterator(){
      return new CustomIterable();
   }
}

Batch:

global class BATCH_ContentDocumentLink implements Database.Batchable < ContentDocumentLink > {

    String query;

    global BATCH_ContentDocumentLink() {
    }

    global Iterable<ContentDocumentLink> start(Database.batchableContext info){ 
       return new CustomIterableExample(); 
   }   

    global void execute(Database.BatchableContext BC, List < Object > scope) {
        System.debug(scope);
    }

    global void finish(Database.BatchableContext BC) {

    }
}