I have a custom object called Questions. This object has a lookup to itself because a question can have additional questions which depend on their parent question. We need to insert 200+ at a time so I wrote an apex class that simply inserts the collection given to it:

global with sharing class QuestionRestController{
   global class RequestBody {
       global List<Question__c> questions;
   }

    @HttpPost   
    global static List<Question__c> createBulk(QuestionRestController.RequestBody req) {
        insert req.questions;
        return req.questions;
    }
}

I get this error: System.DmlException: Insert failed. First exception on row 94; first error: INVALID_FIELD, Foreign key external ID: 966.0 not found for field MyExtId__c in entity Question__c no matter what I try.

I figured I could sort the questions before sending the request so that the parent questions are always inserted first but I still get the errors. I've added debug statements so I could verify the order of the questions prior to inserting and they are ordered correctly. I've also tried to insert each question by itself:

for (Question__c question: req.questions) {
    insert question;
}

But then I get a System.LimitException because I'm sending 200+ questions.

So what is the proper way to insert a list of custom objects which have a lookup to itself when the parent and child are both being inserted with the same request?

Thanks