From e8914196aaa607cf2f5a01ce4f6d0a51129f08d9 Mon Sep 17 00:00:00 2001
From: Finn Bacall <finn.bacall@manchester.ac.uk>
Date: Wed, 29 Jan 2025 16:06:46 +0000
Subject: [PATCH] Fix crash when reading RO-Crates with a single value (instead
 of array) at `hasPart`

---
 lib/ro_crate/reader.rb                        |  4 +-
 test/fixtures/singleton-haspart/a_file        |  1 +
 .../singleton-haspart/ro-crate-metadata.json  | 57 +++++++++++++++++++
 test/reader_test.rb                           |  8 +++
 4 files changed, 69 insertions(+), 1 deletion(-)
 create mode 100644 test/fixtures/singleton-haspart/a_file
 create mode 100644 test/fixtures/singleton-haspart/ro-crate-metadata.json

diff --git a/lib/ro_crate/reader.rb b/lib/ro_crate/reader.rb
index 0eb5ba0..06cbcef 100644
--- a/lib/ro_crate/reader.rb
+++ b/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)
diff --git a/test/fixtures/singleton-haspart/a_file b/test/fixtures/singleton-haspart/a_file
new file mode 100644
index 0000000..190a180
--- /dev/null
+++ b/test/fixtures/singleton-haspart/a_file
@@ -0,0 +1 @@
+123
diff --git a/test/fixtures/singleton-haspart/ro-crate-metadata.json b/test/fixtures/singleton-haspart/ro-crate-metadata.json
new file mode 100644
index 0000000..ba98ce6
--- /dev/null
+++ b/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"
+      }
+    }
+  ]
+}
+
diff --git a/test/reader_test.rb b/test/reader_test.rb
index b3753c4..05bd8f6 100644
--- a/test/reader_test.rb
+++ b/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)