Example of setting a has_one relationship

I would appreciate an example of setting up a has_one relationship. I have the following resources:

App.Api.Item
App.Api.Variant

App.Api.Item
App.Api.Variant

Each resource has an attribute uuid_primary_key :id. I want to establish a 1:1 relationship between the two resources. So, I add the following to App.Api.Item:

relationships do
    has_one :variant, App.Api.Variant
end

relationships do
    has_one :variant, App.Api.Variant
end

I get the following errors/warnings:

warning: invalid association `variant` in schema App.Api.Item: associated schema App.Api.Variant does not have field `item_id`
  lib/app/api/resources/item.ex:1: App.Api.Item (module)

** (EXIT from #PID<0.96.0>) an exception was raised:
    ** (Spark.Error.DslError) [App.Api.Item]
 relationships -> variant:
  Relationship `variant` expects destination field `item_id` to be defined on App.Api.Variant

warning: invalid association `variant` in schema App.Api.Item: associated schema App.Api.Variant does not have field `item_id`
  lib/app/api/resources/item.ex:1: App.Api.Item (module)

** (EXIT from #PID<0.96.0>) an exception was raised:
    ** (Spark.Error.DslError) [App.Api.Item]
 relationships -> variant:
  Relationship `variant` expects destination field `item_id` to be defined on App.Api.Variant

Do I need to define an attribute :item_id in resource App.Api.Variant? If so, what type would it be? Or am I on the wrong path?

7 Replies

waseigoOP•3y ago

Yes, I need to also define the following in App.Api.Variant:

attribute :item_id, :uuid

attribute :item_id, :uuid

Jmanda•3y ago

I think in App.Api.Variant you have to define a belongs_to as supposed to adding attribute :item_id, :uuid, so something like:

relationships do
    belongs_to :item, App.Api.Item
end

relationships do
    belongs_to :item, App.Api.Item
end

ZachDaniel•3y ago

Yeah defining the relationship is the more idiomatic way.

waseigoOP•3y ago

Thank you @Jmanda! And is there a way to recursively Api.load! all relationships, aggregates and calculations on a record that belongs_to records that belongs_to other records?

Jmanda•3y ago

You can take a look at https://ash-hq.org/docs/module/ash/latest/ash-query#function-load-2 for loading nested relationships

Ash HQ

Module: Ash.Query

View the documentation for Ash.Query on Ash HQ.

waseigoOP•3y ago

Thanks, I do that now already, I was wondering if there's a function to load everything that's nested.

ZachDaniel•3y ago

That’s not realistic really because you’d typically have “cycles” I.e a relationship back to the parent.

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Example of setting a has_one relationship

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