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user2070502
user2070502

Reputation: 683

Elixir convert struct to map

I'm trying to convert a struct to a map to be able to clean all the nil values

I'm currently using this code 

  case Nadia.get_updates  do
    {:ok, results} ->
      Map.from_struct(results)
      |> Enum.filter(fn {_, v} -> v != nil end)
      |> Enum.into(%{})

Note: Nadia.get_updates returns the following structure: https://hexdocs.pm/nadia/Nadia.Model.Update.html#t:t/0

Yet I'm always receiving the following error: no function clause matching in Map.from_struct/1

Upvotes: 63

Views: 44865

Answers (4)

Juliano
Juliano

Reputation: 2569

Since v0.15 we have Map.from_struct/1 which does exactly this.

defmodule User do
  defstruct [:name]
end

Map.from_struct(%User{name: "valim"})
#=> %{name: "valim"}

Upvotes: 127

radzserg
radzserg

Reputation: 1396

There's another trick

my_struct = %MyStruct{}
my_map = Map.delete my_struct, :__struct__

Upvotes: 17

Fred the Magic Wonder Dog
Fred the Magic Wonder Dog

Reputation: 9099

FWIW, I wrote a library that will do this kind of thing for you automagically w/o having to pull the data structure apart.

https://github.com/philosophers-stone/transform

This is from the test code: 

test "implement scrub of empty values from map" do
  data = %{ :a => nil, :b => "", :c => "a"}
  replace_empty = fn(string, _d) -> if( string == "", do: nil , else: string) end
  replace_nil = fn(map, _depth) ->  for {k, v} <- map, v != nil , into: %{}, do: {k, v} end
  potion = %{ BitString => replace_empty, Map => replace_nil}

  assert PhStTransform.transform(data, potion) == %{:c => "a"}

end

Note, if data was a list of maps this would still work just fine. The PhStTransform library will just keep pulling the data apart until it finds a map. In your case you would use a replace_nil function that worked on the kinds of structs you are interested in.

Upvotes: 1

Sasha Fonseca
Sasha Fonseca

Reputation: 2313

get_updates([{atom, any}]) ::
  {:ok, [Nadia.Model.Update.t]} |
  {:error, Nadia.Model.Error.t}

If successful it returns a list of Nadia.Model.Update.t. That's why you get that error.

Upvotes: 2

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