Wings: Roundtrip of single value attribute become an array after saving

[elrayle]

Descriptive summary

In a valkyrie resource, saving the resource converts single value attributes from String to Array.

Rationale

The roundtrip conversion from resource to AF object and back to resource should not change the value of an attribute.

Expected behavior

resource = MyResource.new(single_value_attr: "one")
resource. single_value_attr           # "one"
updated_resource = Hyrax.persister.save(resource: resource)
updated_resource. single_value_attr   # "one"

NOTE: single_value_attr is "one" before and after the save

Actual behavior

resource = MyResource.new(single_value_attr: "one")
resource. single_value_attr           # "one"
updated_resource = Hyrax.persister.save(resource: resource)
updated_resource. single_value_attr   # ["one"]

NOTE: single_value_attr is "one" before and an Array ["one"] after the save

Steps to reproduce the behavior

TBD - creating a test to demonstrate the problem

[tpendragon]

@elrayle This happens when single_value_attr is defined as a Valkyrie::Types::String?

[no-reply]

at first glance, i think this is expected Wings behavior.

ActiveFedora/Fedroa still treats these attributes as multi-valued RDF properties, and Wings doesn't try to cast back to a single value, since that risks silent data loss.

[elrayle]

@tpendragon It happens for all single value types for the reason described by @no-reply.

[elrayle]

How Valkyrie handles this [@tpendragon in Slack]...

It’s just if there’s only one value it picks off the first one in the conversion from Fedora->Resource, and then if it’s defined as a Valkyrie::Set the set type conversion takes care of making it an array again.

Valkyrie’s conversion logic for Fedora is mad complicated, but https://github.com/samvera/valkyrie/blob/master/lib/valkyrie/persistence/fedora/persister/orm_converter.rb#L524-L537 is the hunk of code for this.

Postgres (and everything else) uses this: https://github.com/samvera/valkyrie/blob/master/lib/valkyrie/persistence/shared/json_value_mapper.rb#L107-L130

[elrayle]

Closing... Addressed by PR #4607 - wings: handle single value fields for valkyrie native models