How do you write a record to a Mnesia table?

mnesia:write/1 inserts or updates a record inside a transaction — if a record with the same primary key already exists, it's overwritten; otherwise a new one is added.

-record(person, {id, name, age}).

mnesia:transaction(fun() ->
    mnesia:write(#person{id = 1, name = "Ada", age = 34})
end).

Because mnesia:write/1 must run inside a transaction context (typically via mnesia:transaction/1 or mnesia:sync_transaction/1), Mnesia can guarantee the write is applied consistently across every replicated copy of the table, or not at all if the transaction aborts. Trying to call mnesia:write/1 outside of any transaction context raises an error, since there's no transaction for it to participate in.

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