Using an Ecto result as params for a changeset

BrightEyesDavid

I have two schemas which are similar and which each contain the same embedded schema. One represents user-submitted data (submission) and one represents admin-created data which may or may not be based on a user submission (entry).

For entry’s new (from a submission) web admin action, so that the form inputs are prefilled with the submission’s data, how can I convert one Ecto submission result (a struct) and its embedded schemas (also structs) into a nested map in order to use it as params for a new changeset?

This would be from something like:

%MyApp.Submission{
  __meta__: #Ecto.Schema.Metadata<:loaded, "submissions">,
  entries: nil,
  data: %MyApp.Data{
    foo: true,
    TemperatureData: [
      %MyApp.Data.TemperatureOffset{
        Offset: -3,
        Temperature: -24,
        id: "1ffd0e3f-d5d9-4d1e-9a99-ae190dddde08"
      },
      %MyApp.Data.TemperatureOffset{
        Offset: 3,
        Temperature: 10,
        id: "7cd90b5b-19e1-4d4a-a68b-0d783ba76412"
      }
    ],
    id: "0b47e792-fc45-4c48-b476-877ede66aeda"
  },
  id: "0540750a-3ef3-4cf0-aa37-23cda4cb5d39",
  name: "Test"
}

to:

%{
  data: %{
    HVT: true,
    TemperatureData: [
      %{
        Offset: -3,
        Temperature: -24
      },
      %{
        Offset: 3,
        Temperature: 10
      }
    ]
  },
  id: "0540750a-3ef3-4cf0-aa37-23cda4cb5d39",
  name: "Test"
}

(In the example result I’ve removed the embedded schema’s ids, though I’m not sure this is necessary.)

Thanks.

Edit: apologies - I’ve realised (I think) this can be achieved simply by using changeset functions. If I understand correctly, I just need to remove the submission’s id before using it to make a new changeset.

1 comment

/phoenix #ecto #changesets #nested-resources

0 2093 1

2018-06-25 20:37:53 UTC

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BrightEyesDavid

I currently have the following which seems to be doing the trick.

Controller:

def new(conn, %{"from_submission" => from_submission_id}) do
  submission = WorkData.get_submission!(from_submission_id)
  changeset = WorkData.create_entry_changeset_from_submission(submission)
  # ...
end

Context:

def create_entry_changeset_from_submission(%Submission{} = submission) do
  Entry.changeset_from_submission(submission)
end

Entry Schema:

def changeset_from_submission(submission) do
  %Entry{}
  |> changeset(%{})
  |> put_change(:data, submission.data)
  |> put_change(:type, submission.type)
  |> put_change(:name, submission.name)
end

Does this seem like a sane/reasonable way of creating a changeset in order to prefill entry HTML form fields with values from a submission?

It avoids what I get when I try to throw the whole single submission result into a changeset, even after using Map.from_struct/1:

[debug] ** (Ecto.CastError) expected params to be a :map, got: %MyApp.MyModule.WorkData.TemperatureOffsetProfile{foo: true, TemperatureData: [%MyApp.MyModule.WorkData.TemperatureOffset{Offset: -3, Temperature: -24, id: "1ffd0e3f-d5d9-4d1e-9a99-ae190dddde08"}, %MyApp.MyModule.WorkData.TemperatureOffset{Offset: 3, Temperature: 10, id: "7cd90b5b-19e1-4d4a-a68b-0d783ba76412"}], id: "0b47e792-fc45-4c48-b476-877ede66aeda"}

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