getRelationshipOrder() returning null

Question

I'm trying this simple statement and getting null, shouldn't this be returning 1 since its a master-detail relationship? I've tried at API V40,41,42. Is my syntax wrong?

Here's the relevant documentation on DescribeFieldResult.

Anonymous script yielding null:

System.debug('relationshipOrder : ' + OpportunityLineItem.OpportunityId.getDescribe().getRelationshipOrder());

EDIT: My previous example was an attempt to make it more generic since not everyone has Work Orders enabled, my actual issue was with WorkOrderId on WorkOrderLineItem which is a MD relationship) also returning null.

https://i.sstatic.net/VuHYF.jpg (screenshot of relationship)

WorkOrderLineItem.WorkOrderId.getDescribe().getRelationshipOrder() 

Answer 1

It's a Lookup relationship. The expected return value is null. Some standard objects allow Rollup Summary fields despite this configuration. See, for example, this delivered Idea:

Roll-up Summary Fields for Standard Objects (Opp-Opp Line in Winter 08)

The recently announced Summer 07 feature for Roll-up Summary fields is a great step forward. However, it only allows roll-up summaries to be created when a custom, master-detail relationship exists. It would be tremendously useful to extend that same functionality to standard objects and the existing relationships. For example...

Example 1
Create a Roll-up Summary field on the Account object that calculates the SUM of all related Opportunities where Stage = "Closed/Won." This is an obvious win for organizations that wish to easily identify the value of a particular customer in terms of sold business.

Example 2
Create a Roll-up Summary field on the Account object that calculates the COUNT of all related Cases where Type or Status = X. Use your imagination but this could be an easy way for support organizations to identify how many cases a customer has submitted versus their paid support agreement.

Example 3
Create a Roll-up Summary field on the Opportunity Product (line item) object that calculates the COUNT of all related Schedule Entries or the MIN/MAX date for related Schedule Entries. This would be an easy way to show - directly on the Opportunity related list for Products - how many monthly installments have been planned for a product or the first/last month that payment is expected.