Ensure TopKEncoder has correct outputs when model is saved (#1225)

* Remove output_names from base BaseModel.

* Add assertion for output signature of saved model to test_topk_encoder

* Move compile method from BaseModel to Model

* Correct name of structured outputs

* Move compile method back and add special case for TopKOutput

Author: oliverholworthy

merlin/models/tf/models/base.py

@@ -69,6 +69,7 @@
 from merlin.models.tf.outputs.base import ModelOutput, ModelOutputType
 from merlin.models.tf.outputs.classification import CategoricalOutput
 from merlin.models.tf.outputs.contrastive import ContrastiveOutput
+from merlin.models.tf.outputs.topk import TopKOutput
 from merlin.models.tf.prediction_tasks.base import ParallelPredictionBlock, PredictionTask
 from merlin.models.tf.transforms.features import PrepareFeatures, expected_input_cols_from_schema
 from merlin.models.tf.transforms.sequence import SequenceTransform
@@ -446,7 +447,10 @@ def compile(
         if num_v1_blocks > 0:
             self.output_names = [task.task_name for task in self.prediction_tasks]
         else:
-            self.output_names = [block.full_name for block in self.model_outputs]
+            if num_v2_blocks == 1 and isinstance(self.model_outputs[0], TopKOutput):
+                pass
+            else:
+                self.output_names = [block.full_name for block in self.model_outputs]
 
         # This flag will make Keras change the metric-names which is not needed in v2
         from_serialized = kwargs.pop("from_serialized", num_v2_blocks > 0)

tests/unit/tf/core/test_encoder.py

@@ -122,6 +122,15 @@ def test_topk_encoder(music_streaming_data: Dataset):
         loaded_topk_encoder = tf.keras.models.load_model(tmpdir)
     batch_output = loaded_topk_encoder(batch[0])
 
+    output_signature = loaded_topk_encoder.signatures["serving_default"].structured_outputs
+    assert len(output_signature) == 2
+    assert output_signature["scores"] == tf.TensorSpec(
+        shape=(None, TOP_K), dtype=tf.float32, name="scores"
+    )
+    assert output_signature["identifiers"] == tf.TensorSpec(
+        shape=(None, TOP_K), dtype=tf.int32, name="identifiers"
+    )
+
     assert list(batch_output.scores.shape) == [BATCH_SIZE, TOP_K]
     tf.debugging.assert_equal(
         topk_encoder.topk_layer._candidates,