What is a unique relation between content_types?


Let’s say I’m creating a relation between two content_types.

I’m then offered various relation types:

[A has one B], [A has and belongs to one B], [A belongs to many B], [B **has many** A], [A has and belongs to many B], [A has many B]

Then if we go to “Advanced” we’re offered an option to make the relation unique - but what does that mean?

For example: if I select [A has and belongs to many B], but then make it unique - won’t that just de-facto create a [A belongs to many B] relation?


A has and belongs to many B, but we create an A_0 <-> B_0 record, then we try to create an A_1 <-> B_0. I’m thinking this second one would fail, as a relation between an A to a specifc B is unique, thus disabling the second record from existing.

This would mean that:

  1. there can only be as many As as there are Bs

  2. not two As can be related to the same B

Can you please help me think through this?