'What is the difference between a back-reference and a X2X relation?
I am starting with Ent (and ORMs in general) and I have a hard time understanding the difference between a back-reference and a X2X (M2O, O2M, ...) relationship.
The documentation for Ent first mentions that (emphasis mine)
The new edge created in the diagram above is translucent, to emphasize that we don't create another edge in the database. It's just a back-reference to the real edge (relation).
Then it proceeds to say
In this user-pets example, we have a O2M relation between user and its pets. Each user has many pets, and a pet has one owner. If user A adds a pet B using the pets edge, B can get its owner using the owner edge (the back-reference edge).
Note that this relation is also a M2O (many-to-one) from the point of view of the Pet schema.
In which sense this M2O relation is not real? What makes the first one "more real" than the reverse one?
Aren't they equal, just viewed from two different angles?
Sources
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Source: Stack Overflow
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