Sebb
I’m building an Ecto schema to cast a JSON into a struct.
The data looks like this:
%{
name: "Bob",
...
body_parts: [
%{id: "head", count: 1},
%{id: "hands", count: 2},
]
}
I’d like to have the body parts in a map (indexed by their ID) like:
%Person{
body_parts: %{
"head" => %BodyPart{count: 1, id: "head"},
"hands" => %BodyPart{count: 2, id: "hands"}
},
...
name: "Bob"
}
but embeds_many(:body_parts, BodyPart) (obviously) gives me a list.
Is there a clean way to do that? I could just post-process the Person but my schema would be lying then.
If that helps I could change the input to a map.
defmodule BodyPart do
use Ecto.Schema
@primary_key false
embedded_schema do
field(:id, :string)
field(:count, :integer)
end
def changeset(body_part, params) do
Ecto.Changeset.cast(body_part, params, [:id, :count])
end
end
defmodule Person do
use Ecto.Schema
@primary_key false
embedded_schema do
field(:id, :integer)
...
embeds_many(:body_parts, BodyPart)
end
def changeset(params) do
%Person{}
|> Ecto.Changeset.cast(params, [:id, :name, :age, :hobbies, :friends])
|> Ecto.Changeset.cast_embed(:body_parts)
end
end
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dimitarvp
This got me curious: why do you need this connection as a map? Why is the normal embedding not good enough?
Sebb
I’m not using a database but use
Ecto.Schemato load JSON into Elixir Structs.The IDs are used by other objects to reference objects in another collection. So I need the collections indexed by ID.
krasenyp
Maybe use
embeds_oneand do your transformation in thechangesetfunction.Adzz
You’ll probably have to create a custom ecto type for this as the keys look dynamic.
Sebb
What I currently do is use
embeds_manyand transform the list to a map (pull out the ID).The only problem is, that the schema does not reflect reality now. Don’t see how this would get better by using
embeds_one.I thought about that, but after implementing
Ecto.Enumbecause I didn’t understand it I’d rather ask if there is a builtin way. I’m not sure if its worth the effort for just to have a clean schema. Actually I’m not sure if I shouldnt give up the DB-free path and just use Ecto and postgres.IvanR
The transformation of the list to map indicates a core domain model requirement, where the map has a meaning for indexing. And from the JSON’s model perspective represented by schema, it’s ok to have a list. So, It’s an option to have two models and make a transformation between them on the controller level.