Nested dry-struct serialization

Support
1

Hi! Ultimately what I’m trying to do here is implement ActiveRecord serialization for dry-struct, as mentioned here: dry-struct and serializer

I have a struct with reference to another struct, as follows:

  class InventoryPayload < Dry::Struct
     attribute :items, Types::Array.of(Types.Instance(EventTypes::EventLineItem))
  end

  class EventLineItem < Dry::Struct
    transform_keys(&:to_sym)
    attribute :item_id, Types::Integer
    attribute :item_value_in_cents, Types::Integer
  end

When this is dumped to a hash, the initialization logic doesn’t seem to have a good way to turn the nested part of the hash back into a struct:

irb> EventTypes::InventoryPayload.new(items: [{item_id: 1, item_value_in_cents: 1}])
Dry::Struct::Error: [EventTypes::InventoryPayload.new] [{:item_id=>1, :item_value_in_cents=>1}] (Array) has invalid type for :items violates constraints (type?(EventTypes::EventLineItem, {:item_id=>1, :item_value_in_cents=>1}) failed)

The only thing I was able to get working is to add a method InventoryPayload that maps the input hash to EventLineItems. But this seems kind of odd - there should be some way to automatically coerce this? If not, that’s fine, but I’m wondering if I’m missing something.

2

Types.Instance is the problem here. The hash input will fail this check, what you want is a coercible type that will transform a hash into the struct. This is, in fact, how struct objects behave when you use them as types.

class InventoryPayload < Dry::Struct
  attribute :items, Types::Array.of(EventLineItem)
end

[1] pry(main)> event = InventoryPayload.new(items: [{ item_id: 1, item_value_in_cents: 1 }])
=> #<InventoryPayload items=[#<EventLineItem item_id=1 item_value_in_cents=1>]>
[2] pry(main)> InventoryPayload.new(event.to_hash)
=> #<InventoryPayload items=[#<EventLineItem item_id=1 item_value_in_cents=1>]>
3

Ahhh there it is! The docs didn’t show this pattern so I wasn’t aware it was an option. Thanks!