Using manage_relationship with nested relationships

I have three resource modules:

defmodule Patient do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  postgres do
    table "patients"
    repo Repo
  end

  attributes do
    uuid_primary_key(:id)
    attribute(:first_name, :string)
    attribute(:last_name, :string)
    timestamps()
  end

  relationships do
    has_many :event_series, EventSeries
  end
end

defmodule EventSeries do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  postgres do
    table "event_series"
    repo Repo
    
    custom_indexes do
      index [:patient_id, :initial_date], unique: true
    end
  end

  attributes do
    uuid_primary_key(:id)
    attribute(:initial_date, :date)
    timestamps()
  end

  relationships do
    belongs_to :patient, Patient, allow_nil?: false
    has_many :exams, Exam
  end
end

defmodule Exam do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  postgres do
    table "exams"
    repo Repo
  end

  attributes do
    uuid_primary_key(:id)
    attribute(:performed_on, :date)
    timestamps()
  end

  relationships do
    belongs_to :event_series, EventSeries, allow_nil?: false
  end
end

defmodule Patient do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  postgres do
    table "patients"
    repo Repo
  end

  attributes do
    uuid_primary_key(:id)
    attribute(:first_name, :string)
    attribute(:last_name, :string)
    timestamps()
  end

  relationships do
    has_many :event_series, EventSeries
  end
end

defmodule EventSeries do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  postgres do
    table "event_series"
    repo Repo
    
    custom_indexes do
      index [:patient_id, :initial_date], unique: true
    end
  end

  attributes do
    uuid_primary_key(:id)
    attribute(:initial_date, :date)
    timestamps()
  end

  relationships do
    belongs_to :patient, Patient, allow_nil?: false
    has_many :exams, Exam
  end
end

defmodule Exam do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  postgres do
    table "exams"
    repo Repo
  end

  attributes do
    uuid_primary_key(:id)
    attribute(:performed_on, :date)
    timestamps()
  end

  relationships do
    belongs_to :event_series, EventSeries, allow_nil?: false
  end
end

With this in place, I was able to figure out how to insert patients into the database pretty easily, however my problems arose when trying to do the exams. The exams are loaded from an outside data source where we derive the event series based on a date value. So what I tried to do was:

Exam
|> Ash.Changeset.for_create(:create, %{performed_on: performed_on})
|> Ash.Changeset.manage_relationship(:event_series, %{patient_id: patient_id, initial_date: examdate}, type: :append_and_remove, on_no_match: :create)
|> Api.create()

Exam
|> Ash.Changeset.for_create(:create, %{performed_on: performed_on})
|> Ash.Changeset.manage_relationship(:event_series, %{patient_id: patient_id, initial_date: examdate}, type: :append_and_remove, on_no_match: :create)
|> Api.create()

When doing this, an error is returned saying that the event series is invalid because the patient relationship is not defined. Is it possible to do this with a call to manage_relationship or am I fundamentally missing something? Thanks so much for any assistance, Ash is very cool so far!

12 Replies

ZachDaniel•3y ago

So you have two options. To do it the way you're doing it, you can just add attribute_writable?: true to the patient relationship. And actually that is how I'd suggest that you do it, so lets just leave it at the first option. With that said, I'd suggest defining a custom action for this logic, and putting it in the resource.

# on exam

actions do
  create :create do
    accept [:performed_on]
    argument :event_series, :map, allow_nil?: false
    change manage_relationship(:event_series, type: :append_and_remove, on_no_match: :create)
  end
end

# on exam

actions do
  create :create do
    accept [:performed_on]
    argument :event_series, :map, allow_nil?: false
    change manage_relationship(:event_series, type: :append_and_remove, on_no_match: :create)
  end
end

Then you can do Exam |> Ash.Changeset.for_create(:create, %{performed_on: performed_on, event_series: %{...}}) |> Api.create()

mylanconnollyOP•3y ago

Thanks so much! I tried the first option and that solved my problem for the meantime. I'm going to probably refactor the code to use the custom actions, though, since that looks cleaner for what I'm ultimately trying to accomplish. thanks for answering so quickly and for the hard work on Ash!

ZachDaniel•3y ago

Generally speaking, you should prefer to put as much of your business logic behind your resources as possible, as they are meant to be more "domain objects" than "database objects" (although the two intersect often).

mylanconnollyOP•3y ago

That makes sense, I'll try to keep that in mind. It's a different way compared to what I'm used to but I can definitely see the usefulness of it I just encountered another hiccup. I updated the code slightly:

defmodule EventSeries do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  postgres do
    table "event_series"
    repo Repo
  end

  attributes do
    uuid_primary_key(:id)
    attribute(:initial_date, :date)
    timestamps()
  end
  
  identities do
    identity :patient_initial_date, [:patient_id, :initital_date]
  end

  relationships do
    belongs_to :patient, Patient, allow_nil?: false
    has_many :exams, Exam
  end
end

defmodule EventSeries do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  postgres do
    table "event_series"
    repo Repo
  end

  attributes do
    uuid_primary_key(:id)
    attribute(:initial_date, :date)
    timestamps()
  end
  
  identities do
    identity :patient_initial_date, [:patient_id, :initital_date]
  end

  relationships do
    belongs_to :patient, Patient, allow_nil?: false
    has_many :exams, Exam
  end
end

(note that I removed the custom_indexes block and replaced it with an identies block). I changed the changeset logic somewhat to include the identity:

Exam
|> Ash.Changeset.for_create(:create, %{performed_on: performed_on})
|> Ash.Changeset.manage_relationship(:event_series, %{patient_id: patient_id, initial_date: examdate}, type: :append_and_remove, on_no_match: :create, use_identities: [:patient_initial_date])
|> Api.create()

Exam
|> Ash.Changeset.for_create(:create, %{performed_on: performed_on})
|> Ash.Changeset.manage_relationship(:event_series, %{patient_id: patient_id, initial_date: examdate}, type: :append_and_remove, on_no_match: :create, use_identities: [:patient_initial_date])
|> Api.create()

It is possible for multiple exams to exist in the same series, so I was hoping it'd look up the event series in the database first, but it doesn't seem to be doing that. Is this something I can change or should I just create the series as a separate action at this point? Just trying to wrap my head around it. Thanks!

ZachDaniel•3y ago

What should happen if it looks it up?

mylanconnollyOP•3y ago

I was hoping it'd use the event series that it found in the database

ZachDaniel•3y ago

That is what append_and_remove should do

mylanconnollyOP•3y ago

hm, strange... I might be doing something wrong. I see some errors about a violated uniqueness constraint in those cases where the series already exists in the database

ZachDaniel•3y ago

lol so we should be giving you an error for this initital_date I guess we're allowing an identity with an invalid field 😢

mylanconnollyOP•3y ago

hmm, like my resource is messed up or the data is invalid?

ZachDaniel•3y ago

no there is a typo there inititial_date -> initial_date

mylanconnollyOP•3y ago

lol woops. ok good catch. I should probably call it a night, it looks like 🙂 working like a charm now. thanks again!

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Using manage_relationship with nested relationships

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