this post was submitted on 11 May 2024
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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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[–] deegeese@sopuli.xyz 3 points 6 months ago (1 children)

The JSON version of this is to store an array of relation objects which express the weights.

In my opinion the main advantage of a “join table” in your situation is the ability to look up the relationship from either direction while only storing a single copy of it.

If you store the relation in the object, becomes very easy for A’s relation to B to get out of sync from B’s relation to A.

[–] andrew@lemmy.stuart.fun 2 points 6 months ago

The other related advantage is being able to update data about a given B once, instead of everywhere it occurs as a child in A.