Replace List within Struct with another List

Question

I have this struct:

%MyApp.ScoreTable{
  __meta__: #Ecto.Schema.Metadata<:loaded, "score_tables">,
  id: "7f320636-2176-4af2-9207-6251416dd6c2",
  inserted_at: ~N[2018-11-04 21:08:26.024733],
  question: #Ecto.Association.NotLoaded<association :question is not loaded>,
  question_id: "dadc6e57-49f4-4339-9c0f-d40dbc6df534",
  season: #Ecto.Association.NotLoaded<association :season is not loaded>,
  season_id: "c356bae0-bee8-45df-b035-dc117908bebd",
  table_details: %MyApp.TableDetails{
    information: [
      %{
        "team_id" => "7ca4c7ac-850b-4f27-8b6e-1feeb1e0629b",
        "team_score" => "N/A"
      },
      %{"team_id" => "f78c069d-1500-4cfe-a201-13223c417f82", "team_score" => 5},
      %{"team_id" => "4b3459a0-f81c-436d-a68c-3a00dea62a2d", "team_score" => 5},
      %{"team_id" => "9dff5653-dee4-4fef-9d91-7d53f3861275", "team_score" => 10},
      %{"team_id" => "dab53fe6-419b-4a86-a1c6-9c1f65445e12", "team_score" => 15}
    ]
  },
  updated_at: ~N[2018-11-04 21:08:26.024739]
}

And I want to replace fully the table_details.information list with this one:

[
  %{
    "team_id" => "cebda2b5-26e1-4804-8529-17367155db06",
    "team_place" => 1,
    "team_score" => 5
  },
  %{
    "team_id" => "ea800d1c-a079-4f6f-9a91-2a085779dfa9",
    "team_place" => 1,
    "team_score" => 5
  },
  %{
    "team_id" => "2d9253fa-63b7-45dd-bf8f-370598a1424c",
    "team_place" => 3,
    "team_score" => 10
  },
  %{
    "team_id" => "1748f471-08ae-49ed-844b-0fe1bc539a8f",
    "team_place" => 4,
    "team_score" => 15
  },
  %{
    "team_id" => "df2f5102-4e6f-4480-8167-ebe0548cd4ba",
    "team_place" => 5,
    "team_score" => "N/A"
  }
]

To be clear, I want to wholesale swap the old list with the new list of maps. How can I achieve this?

Paweł Obrok · Accepted Answer · 2018-11-04 22:12:54Z

2

You can use the struct update syntax. Assuming your whole datastructure is stored in data and the new list in new_information, something like this will work:

data = %{data | table_details: %{data.table_details | information: new_information}}

Note that the update syntax creates a new version of the structure, so you need to assign it to a variable or return it from your function as appropriate.

Sometimes it's more clear what you're trying to achieve if you use Access with the associated Kernel macros. In this case:

data = put_in(data, [Access.key(:table_details), Access.key(:information)], new_information)

This basically does the same thing, but you only need to specify the path to the change and what to change. In the previous example one might make a mistake like %{other_data.table_details | information: new_information} (note other_data instead of data), in this case it's easy to see at a glance that only that one part of the structure is modified.

answered Nov 4, 2018 at 22:12

Paweł Obrok

23.3k8 gold badges77 silver badges70 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Bitwise Over a year ago

That is some awesome information. Thanks for the help.

Collectives™ on Stack Overflow

Replace List within Struct with another List

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related