How Do I Configure Fabricator to Use a Custom Foreign Key for Rails STI Associations?

Based on your description, the problem is that Fabrication is automatically creating an attribute key called "organization_id" from your association declaration:

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belongs_to :organization, foreign_key: 'type_id'

Fabrication isn’t aware of the custom foreign key (type_id) and so produces "organization_id". When Rails tries to assign organization_id to your OrganizationUser (which inherits from AdminUser), it raises an ActiveModel::UnknownAttributeError because there is no organization_id column.

To fix this, you have a couple of options:

1. Update Your Fabricator to Use the Correct Foreign Key

Instead of fabricating the association using the name “organization”, you can explicitly assign the organization using the correct attribute key. For example, if you have another fabricator for Organization (or the appropriate model), you can do:

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Fabricator(:admin_user) do
  email { Forgery(:internet).email_address }
  first_name { Forgery(:name).first_name }
  last_name { Forgery(:name).last_name }
end

Fabricator(:organization_user, from: :admin_user, class_name: :organization_user) do
  type_id { Fabricate(:organization).id }
end

Here, instead of simply writing organization, you assign the organization’s id to type_id, which matches your association's foreign key.

2. Customize the Fabrication for Associations

If you want to continue using the association helper (i.e. organization), you need to let Fabrication know about the custom key. Fabrication doesn’t automatically look up the association’s foreign_key option. One workaround is to overwrite the attribute in your fabricator block after the association is set:

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Fabricator(:organization_user, from: :admin_user, class_name: :organization_user) do
  organization do
    Fabricate(:organization)
  end

  # Override the automatically generated organization_id attribute with type_id
  after_build do |user|
    user.type_id = user.organization.id if user.organization
    # Remove the incorrect attribute if needed (depending on how Fabrication handles it)
    user.attributes.delete('organization_id')
  end
end

This way, once the organization is built and assigned to the user, you can manually copy its id into type_id and remove the incorrect organization_id attribute.

Additional Note on STI

Since your OrganizationUser inherits from AdminUser, Rails is using single table inheritance (STI), which means a “type” column is usually maintained automatically. Make sure your database is set up accordingly so that Rails sets the type column to "OrganizationUser" when you instantiate a record of that class.

Conclusion

The core of the issue is that when using a custom foreign key (type_id), Fabrication defaults to generating association_name + _id (i.e. organization_id). By updating your fabricators to assign the organization id to the correct attribute (type_id) or by overriding the generated attribute, you can resolve the error.

If you have further questions about Rails plugins, factories, or associations, feel free to ask!