fix: Make all reference fields optional

Fixes #176

Author: olafmersmann

SCHEMA.md

@@ -251,7 +251,7 @@ constraints:
 ### Reference
 
 Bibliographic pointer. 
-Requires a `title` and `authors` and optionally includes a `link` to the material.
+Requires either a `title` or a `link` and optionally a list of  `authors`.
 
 ```yaml
 references:

src/opltools/schema.py

@@ -73,16 +73,18 @@ def __hash__(self):
 
 
 class Reference(BaseModel):
-    title: str
-    authors: list[str]
+    title: str | None = None
+    authors: list[str] | None = None
     link: Link | None = None
 
+    @model_validator(mode="after")
+    def _validate(self) -> Self:
+        if self.title is None and self.link is None:
+            raise ValueError("References must have either a title or a link.")
+        return self
+
     def __hash__(self):
-        return (
-            hash(self.title)
-            + sum([hash(author) for author in self.authors])
-            + hash(self.link)
-        )
+        return hash(self.title) + hash(self.link)
 
 
 class Usage(BaseModel):

tests/test_reference.py

@@ -5,20 +5,24 @@
 
 
 class TestReference:
-    def test_minimal(self):
-        ref = Reference(title="A paper", authors=["Alice", "Bob"])
+    def test_only_author(self):
+        ref = Reference(title="A paper")
         assert ref.title == "A paper"
-        assert ref.authors == ["Alice", "Bob"]
+        assert ref.authors is None
         assert ref.link is None
 
-    def test_with_link(self):
+    def test_only_link(self):
+        ref = Reference(link=Link(url="https://example.org"))
+        assert ref.link.url == "https://example.org"
+
+    def test_full(self):
         ref = Reference(
             title="A paper",
             authors=["Alice"],
             link=Link(url="https://example.org"),
         )
         assert ref.link.url == "https://example.org"
 
-    def test_requires_authors(self):
+    def test_requires_title_or_link(self):
         with pytest.raises(ValidationError):
-            Reference(title="A paper")
+            Reference(authors=["A paper"])