What’s the safe way to decode a JSON string into a struct? I want to avoid calling String.to_atom. Jason.decode can give me a map with string keys, but struct() expects atom keys.

I don’t know when it was introduced, but I guess it is somewhat relevant if someone stumbles upon it. :keys options offers :atoms! which only convert to already known atoms… therefore mitigating the DoS risk.

that’s nice. Say I have this typespec: @type foo :: :bar | :baz is :bar an exisiting atom now? Yes it is: _a = :foo String.to_existing_atom("foo") String.to_existing_atom("bar") String.to_existing_atom("non_exsisting") * 1st argument: not an already existing atom :erlang.binary_to_existin…

You can also use an ecto schema then cast to the struct. you can also use helpers to make the casting more generic. That means the atoms will always exist because they’ll be in the function definition, but requires that you know the shape of the json ahead of time a bit. Which may or may not work f…

[image] Adzz: You can also use an ecto schema then cast to the struct. you can also use helpers to make the casting more generic. Just tried that and noticed, that Ecto does not know a :atom type: Ecto.Schema — Ecto v3.14.0 Also I can’t explicitly set a :id field (:id is already set on schem…

[image] Sebb: Also I can’t explicitly set a :id field (:id is already set on schema) but each element in my JSON-collection has an id. I think that @primary_key false would to the job. By default, every schema has an :id primary key.

[image] Sebb: Just tried that and noticed, that Ecto does not know a :atom type: Ecto.Schema — Ecto v3.7.1 If you’re casting JSON into something like the @type foo :: :bar | :baz from a previous post, a specific Ecto.Type will be safer and clearer than the non-existing :atom field type.

Thanks guys, works like a charm. Am I doing it right? In my data I have static stuff (here: hobbies and jobs which can be referenced in a list or as a single atom, this works). Also I have data (here person) that has an integer ID. These objects may reference each other (here friends) reference …

Quick question: Why not use Ecto.Enum for the job and {:array, Ecto.Enum} for the hobbies?

I need a real Atom-Type (which Ecto does not offer). I another context, hobbies may be used as a single atom. (like job).

[image] Sebb: But I can’t do that with persons referencing other persons, because they may not be loaded yet. Conceptually, you can’t determine if a field like friends has valid values in it without a larger context than the single Person. When persisting things to the database, the database…

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How to decode a JSON into a struct safely?

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agreif November 1, 2022, 7:09pm 27

thanks!