user974881
Hello,
I’m trying to use DETS to store a struct, so I know that for this, I need to use the keypos option to tell elixir where it should get the key, so it’s value would be #struct.key, but in elixir, I don’t know how to do it.
I have tried :key, %Struct.key, %Struct[}.key, #struct.key and also without keypos, but none have worked.
How do I use DETS to store a struct? I have also checked in Elixir’s source code and documentation but haven’t found it, I guess this is because it comes from erlang.
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al2o3cr
The
#record.keysyntax is for records; Elixir structs are not records, they are maps.DETS stores tuples, so records fit naturally.
You’ll need to either produce a tuple from your struct, so that
%SomeStruct{key: 123}is stored as{123, %SomeStruct{key: 123}}or transform the struct to a record (see theRecorddocs for some Elixir helpers).One possible gotcha: for the “convert to a record” case, I don’t see a clear Elixir equivalent to
#record.keyto get a tuple position from a field nameEdit: thanks to @lud for calling out what I totally skimmed past - if you said
defrecord :user, ...thenuser(:some_field)is the zero-based index ofsome_fieldin the record. That will work as-is if you want to access the field withKernel#elem, but you’ll need to explicitly add one if you pass it to ETS askeypos(which expects a 1-based index!).user974881
Well thanks, I thought structs were records, didn’t know it was a separate thing, I’ll just use a record instead of a struct now.
lud
It’s
record_macro(:key)!