Handle singleton hasPart

lib/ro_crate/reader.rb

@@ -204,7 +204,9 @@ def self.initialize_crate(entity_hash, source, crate_class: ROCrate::Crate, cont
     # @param entity_hash [Hash] A Hash containing all the entities in the @graph, mapped by their @id.
     # @return [Array<ROCrate::File, ROCrate::Directory>] The extracted DataEntity objects.
     def self.extract_data_entities(crate, source, entity_hash)
-      (crate.raw_properties['hasPart'] || []).map do |ref|
+      parts = crate.raw_properties['hasPart'] || []
+      parts = [parts] unless parts.is_a?(Array)
+      parts.map do |ref|
         entity_props = entity_hash.delete(ref['@id'])
         next unless entity_props
         entity_class = ROCrate::DataEntity.specialize(entity_props)

test/fixtures/singleton-haspart/a_file

@@ -0,0 +1 @@
+123

test/fixtures/singleton-haspart/ro-crate-metadata.json

@@ -0,0 +1,57 @@
+{
+  "@context": [
+    "https://w3id.org/ro/crate/1.1/context",
+    "https://w3id.org/ro/terms/workflow-run/context"
+  ],
+  "@graph": [
+    {
+      "@id": "./",
+      "@type": "Dataset",
+      "datePublished": "2025-01-28T02:44:51.523Z",
+      "hasPart": {
+        "@id": "a_file"
+      },
+      "dateCreated": "2025-01-28T02:45:05.906Z",
+      "dateModified": "2025-01-28T02:44:51.523Z",
+      "description": "Something",
+      "license": {
+        "@id": "https://spdx.org/licenses/MIT"
+      },
+      "mainEntity": {
+        "@id": "a_file"
+      },
+      "name": "An RO-Crate containing just a single item"
+    },
+    {
+      "@id": "ro-crate-metadata.json",
+      "@type": "CreativeWork",
+      "conformsTo": [
+        {
+          "@id": "https://w3id.org/ro/crate/1.1"
+        },
+        {
+          "@id": "https://w3id.org/workflowhub/workflow-ro-crate/1.0"
+        }
+      ],
+      "about": {
+        "@id": "./"
+      }
+    },
+    {
+      "@id": "a_file",
+      "@type": [
+        "File",
+        "ComputationalWorkflow",
+        "SoftwareSourceCode"
+      ],
+      "contentSize": 4,
+      "description": "A workflow",
+      "encodingFormat": "text/plain",
+      "name": "a_file",
+      "programmingLanguage": {
+        "@id": "https://example.com/workflow_format"
+      }
+    }
+  ]
+}
+

test/reader_test.rb

@@ -373,6 +373,14 @@ class ReaderTest < Test::Unit::TestCase
     assert_equal 'At the root', crate.name
   end
 
+  test 'reads crate with singleton hasPart' do
+    crate = ROCrate::Reader.read(fixture_file('singleton-haspart').path)
+
+    data = crate.data_entities
+    assert_equal 1, data.length
+    assert_equal 'a_file', data.first.name
+  end
+
   private
 
   def check_exception(exception_class)