Better way to extract json map into struct - json

Question

I'm new to elixir and I want to parse a json file. One of the parts is a question answer array of objects.
[
{
"questionId":1,
"question":"Information: Personal Information: First Name",
"answer":"Joe"
},
{
"questionId":3,
"question":"Information: Personal Information: Last Name",
"answer":"Smith"
},
...
]
I know what questionId's I want and I'm going to make a map for 1 = First Name, 2 = Last Name.
But currently I'm doing the following to put the data into the struct.
defmodule Student do
defstruct first_name: nil, last_name: nil, student_number: nil
defguard is_first_name(id) when id == 1
defguard is_last_name(id) when id == 3
defguard is_student_number(id) when id == 7
end
defmodule AFMC do
import Student
#moduledoc """
Documentation for AFMC.
"""
#doc """
Hello world.
## Examples
iex> AFMC.hello
:world
"""
def main do
get_json()
|> get_outgoing_applications
end
def get_json do
with {:ok, body} <- File.read("./lib/afmc_import.txt"),
{:ok,body} <- Poison.Parser.parse(body), do: {:ok,body}
end
def get_outgoing_applications(map) do
{:ok,body} = map
out_application = get_in(body,["outgoingApplications"])
Enum.at(out_application,0)
|> get_in(["answers"])
|> get_person
end
def get_person(answers) do
student = Enum.reduce(answers,%Student{},fn(answer,acc) ->
if Student.is_first_name(answer["questionId"]) do
acc = %{acc | first_name: answer["answer"]}
end
if Student.is_last_name(answer["questionId"]) do
acc = %{acc | last_name: answer["answer"]}
end
if Student.is_student_number(answer["questionId"]) do
acc = %{acc | student_number: answer["answer"]}
end
acc
end)
IO.inspect "test"
s
end
end
I'm wondering what is a better way to do get_person with out having to do if statements. If I know I will be mapping 1 to questionId 1 in the array of objects.
The data will then be saved into a DB.
Thanks

Answer 1

I'd store a mapping of id to field name. With that you don't need any if inside the reduce. Some pattern matching will also make it unnecessary to do answer["questionId"] etc.
defmodule Student do
defstruct first_name: nil, last_name: nil, student_number: nil
#fields %{
1 => :first_name,
3 => :last_name,
7 => :student_number
}
def parse(answers) do
Enum.reduce(answers, %Student{}, fn %{"questionId" => id, "answer" => answer}, acc ->
%{acc | #fields[id] => answer}
end)
end
end
IO.inspect(
Student.parse([
%{"questionId" => 1, "question" => "", "answer" => "Joe"},
%{"questionId" => 3, "question" => "", "answer" => "Smith"},
%{"questionId" => 7, "question" => "", "answer" => "123"}
])
)
Output:
%Student{first_name: "Joe", last_name: "Smith", student_number: "123"}
Edit: to skip ids not present in the map, change:
%{acc | #fields[id] => answer}
to:
if field = #fields[id], do: %{acc | field => answer}, else: acc