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I'm going through the Trailhead training (here), and see the following two snippets which seem to disagree:

"It’s possible to change a lookup relationship to a master-detail relationship, but not the other way around. Hence, if you’re in doubt which one to use, it’s best to start with a lookup relationship. If you later decide you need the features of a master-detail relationship, you can change it.

And later on the same page I find:

"If you delete the primary master-detail relationship or convert it to a lookup relationship, the secondary master object becomes primary."

These seem at odds to me, so either (1) I'm misunderstanding what it's saying or (2) there is a discrepancy in the documentation. Which is it? If I'm just misunderstanding, can someone explain what it really means?

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From the Salesforce documentation: Considerations for Relationships

Converting Relationships

You can convert a master-detail relationship to a lookup relationship as long as no roll-up summary fields exist on the master object.

You can convert a lookup relationship to a master-detail relationship, but only if the lookup field in all records contains a value.

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  • Then do you think the first quote in my post just plain wrong? Or just an inaccurate simplification because they haven't gone over roll-up summaries?
    – loneboat
    Mar 11, 2015 at 20:08
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    When in doubt, trust the official documentation. Trailhead's statement is without question, incorrect.
    – Mark Pond
    Mar 11, 2015 at 20:17
  • @MarkPond are there any considerations specifically to doing this in a managed package?
    – NSjonas
    Jun 30, 2017 at 23:28
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    @NSjonas yes there are - in a managed package, the field data type is locked and cannot be changed. developer.salesforce.com/docs/atlas.en-us.packagingGuide.meta/…
    – Mark Pond
    Jul 1, 2017 at 18:14
  • Just a note, the fields have to be hard deleted. If they're still in your Recycle Bin you will remain blocked.
    – Adrian Larson ♦
    Apr 18, 2018 at 17:26
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Yes, this is a known issue. Mark Pond is correct, our information in that unit on Trailhead is inaccurate. You can convert as long as there are no RSF fields. https://help.salesforce.com/HTViewHelpDoc?id=relationships_considerations.htm&language=en_US

We've got the fix teed up and ready to go in our next release.

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