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Benefits of a join table vs. array to express relations? (outside of SQL) (lemy.lol)

submitted 6 months ago by matcha_addict@lemy.lol to c/programming@programming.dev

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I am building an application that is using JSON / XML files to persist data. This is why I indicated "outside of SQL" in the title.

I understand one benefit of join tables is it makes querying easier with SQL syntax. Since I am using JSON as my storage, I do not have that benefit.

But are there any other benefits when using a separate join table when expressing a many-to-many relationship? The exact expression I want to express is one entity's dependency on another. I could do this by just having a "dependencies" field, which would be an array of the IDs of the dependencies.

This approach seems simpler to me than a separate table / entity to track the relation. Am I missing something?

Feel free to ask for more context.

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[–] mox@lemmy.sdf.org 4 points 6 months ago (2 children)

Conceptually, the benefit of a join table is to allow many-to-many relations. That's it.

If I understand you correctly, your relations are one-to-many, so a join table would just be needless complexity.

[–] SzethFriendOfNimi@lemmy.world 2 points 6 months ago

And to cover atomicity. Child records deleted when a parent record is, etc.

[–] matcha_addict@lemy.lol 1 points 6 months ago (1 children)

The list would still allow a many-to-many relationship. Let demonstrate:

entity A and entity B both have 2 members: A-1, A-2, B-1, and B-2.

we add a "relations" field to entity A, which is a list of IDs from B, describing the list of B's that A is related to.

A-1 has the relations field as: [B-1, B-2] and A-2 has [B-1, B-2].

As you can see, this is a many-to-many relationship. Each of our entities is tied to multiple entities. So this is many on both sides, hence many to many

[–] mox@lemmy.sdf.org 1 points 6 months ago* (last edited 6 months ago) (1 children)

That's overly complicated to my eyes, and not really relevant. The point I was trying to make is just that a join table is unnecessary in the situation you originally described.

[–] matcha_addict@lemy.lol 1 points 6 months ago

What I described in the comment above is the same thing I originally described, but expanded.

A dependency relation can still be many to many (and in my case, it is). The comment above gives an example to prove it.