implement target getters for BaseAnnotationList (#297)

* implement target_layers and target_fields properties for BaseAnnotationList

* rename target_fields to targets; remove hasattr check; add target and target_layer

* add tests for targets, target, target_layers, and target_layer

src/pytorch_ie/core/document.py

@@ -351,6 +351,39 @@ def pop(self, index: int = -1) -> T:
         ann.set_targets(None)
         return ann
 
+    @property
+    def targets(self) -> dict[str, Any]:
+        return {
+            target_field_name: getattr(self._document, target_field_name)
+            for target_field_name in self._targets
+        }
+
+    @property
+    def target(self) -> Any:
+        tgts = self.targets
+        if len(tgts) != 1:
+            raise ValueError(
+                f"The annotation layer has more or less than one target: {self._targets}"
+            )
+        return list(tgts.values())[0]
+
+    @property
+    def target_layers(self) -> dict[str, "AnnotationList"]:
+        return {
+            target_name: target
+            for target_name, target in self.targets.items()
+            if isinstance(target, AnnotationList)
+        }
+
+    @property
+    def target_layer(self) -> "AnnotationList":
+        tgt_layers = self.target_layers
+        if len(tgt_layers) != 1:
+            raise ValueError(
+                f"The annotation layer has more or less than one target layer: {list(tgt_layers.keys())}"
+            )
+        return list(tgt_layers.values())[0]
+
 
 class AnnotationList(BaseAnnotationList[T]):
     def __init__(self, document: "Document", targets: List["str"]):

tests/test_document.py

@@ -504,3 +504,56 @@ class TestDocument(Document):
         ),
     ):
         doc = TestDocument(text="text1")
+
+
+def test_annotation_list_targets():
+    @dataclasses.dataclass
+    class TestDocument(Document):
+        text: str
+        entities1: AnnotationList[LabeledSpan] = annotation_field(target="text")
+        entities2: AnnotationList[LabeledSpan] = annotation_field(target="text")
+        relations1: AnnotationList[BinaryRelation] = annotation_field(target="entities1")
+        relations2: AnnotationList[BinaryRelation] = annotation_field(
+            targets=["entities1", "entities2"]
+        )
+
+    doc = TestDocument(text="text1")
+
+    # test getting all targets
+    assert doc.entities1.targets == {"text": doc.text}
+    assert doc.entities2.targets == {"text": doc.text}
+    assert doc.relations1.targets == {"entities1": doc.entities1}
+    assert doc.relations2.targets == {"entities1": doc.entities1, "entities2": doc.entities2}
+
+    # test getting a single target
+    assert doc.entities1.target == doc.text
+    assert doc.entities2.target == doc.text
+    assert doc.relations1.target == doc.entities1
+    # check that the target of relations2 is not set because it has more than one target
+    with pytest.raises(ValueError) as excinfo:
+        doc.relations2.target
+    assert (
+        str(excinfo.value)
+        == "The annotation layer has more or less than one target: ['entities1', 'entities2']"
+    )
+
+    # test getting all target layers
+    assert doc.entities1.target_layers == {}
+    assert doc.entities2.target_layers == {}
+    assert doc.relations1.target_layers == {"entities1": doc.entities1}
+    assert doc.relations2.target_layers == {"entities1": doc.entities1, "entities2": doc.entities2}
+
+    # test getting a single target layer
+    with pytest.raises(ValueError) as excinfo:
+        doc.entities1.target_layer
+    assert str(excinfo.value) == "The annotation layer has more or less than one target layer: []"
+    with pytest.raises(ValueError) as excinfo:
+        doc.entities2.target_layer
+    assert str(excinfo.value) == "The annotation layer has more or less than one target layer: []"
+    assert doc.relations1.target_layer == doc.entities1
+    with pytest.raises(ValueError) as excinfo:
+        doc.relations2.target_layer
+    assert (
+        str(excinfo.value)
+        == "The annotation layer has more or less than one target layer: ['entities1', 'entities2']"
+    )