jhefreyzz
Transforming list of structs to map
Hi,
Is there an easier way to convert a list of structs to map. Extracting fields from the struct and in the nested struct and make it a map.
The list of struct:
[
%Kaiwa.Chat.Message{
__meta__: #Ecto.Schema.Metadata<:loaded, "messages">,
id: 1,
inserted_at: ~N[2020-04-03 11:46:24],
room: #Ecto.Association.NotLoaded<association :room is not loaded>,
room_id: 1,
text: "this is a test message",
updated_at: ~N[2020-04-03 11:46:24],
user: %Kaiwa.Accounts.User{
__meta__: #Ecto.Schema.Metadata<:loaded, "users">,
id: 1,
inserted_at: ~N[2020-04-02 04:10:00],
messages: #Ecto.Association.NotLoaded<association :messages is not loaded>,
name: "Mr Testing",
password: nil,
password_hash: "$argon2id$v=19$m=131072,t=8,p=4$26a9JgOy+rmuhjQ7WZD1bg$ZJe55e9UdfrWqm0E4rMnGFG7mA/Wyr7fWdi1f1tZP+8",
rooms: #Ecto.Association.NotLoaded<association :rooms is not loaded>,
updated_at: ~N[2020-04-02 04:10:00],
username: "test"
},
user_id: 1
}
]
My attempt:
Enum.map(messages, fn message ->
user = Map.from_struct(message.user)
%{
message_id: message.id,
text: message.text,
created_at: message.inserted_at,
user_id: user.id,
name: user.name
}
end)
Expected result:
[
%{
created_at: ~N[2020-04-03 11:46:24],
message_id: 1,
name: "Mr Testing",
text: "this is a test message",
user_id: 1
}
]
Is there a better way to achieve the expected result or my attempt is okay?
Marked As Solved
benwilson512
user_map = Map.take(user, [:name, :id, :username])
Also Liked
benwilson512
This is going to include a lot of keys you don’t want like __meta__ and password_hash (very bad). If you’re trying to create a JSON response for an API I recommend just explicitly making maps for each of the things you want to expose.
dimitarvp
I would be more comfortable with something that asserts the shape of the data it receives so I can catch bugs early:
Enum.map(
messages,
fn %{
id: message_id,
text: text,
inserted_at: created_at,
user: %{id: user_id, name: name}
} ->
%{
message_id: message_id,
text: text,
created_at: created_at,
user_id: user_id,
name: name
}
end
)
If even one message doesn’t comply with the expected structure you’ll get an appropriate error. Although to be fair, your code would also blow up but IMO in a slightly less intuitive fashion. I’d prefer mine because it also makes intent clearer.







