Add ability for extractor to reference another pipeline in applicatio…

…ns, closes #501

src/python/txtai/app/base.py

@@ -102,6 +102,9 @@ def pipes(self):
             if "." in key:
                 pipelines.append(key)
 
+        # Move dependent pipelines to end of list
+        pipelines = sorted(pipelines, key=lambda x: x in ["similarity", "extractor"])
+
         # Create pipelines
         for pipeline in pipelines:
             if pipeline in self.config:
@@ -115,6 +118,11 @@ def pipes(self):
                 if pipeline == "extractor" and "similarity" not in config:
                     # Add placeholder, will be set to embeddings index once initialized
                     config["similarity"] = None
+
+                    # Resolve reference pipeline, if necessary
+                    if config.get("path") in self.pipelines:
+                        config["path"] = self.pipelines[config["path"]]
+
                 elif pipeline == "similarity" and "path" not in config and "labels" in self.pipelines:
                     config["model"] = self.pipelines["labels"]
 

test/python/testapi/testembeddings.py

@@ -21,13 +21,17 @@
 # Allow indexing of documents
 writable: True
 
+# Questions settings
+questions:
+    path: distilbert-base-cased-distilled-squad
+
 # Embeddings settings
 embeddings:
     path: sentence-transformers/nli-mpnet-base-v2
 
 # Extractor settings
 extractor:
-    path: distilbert-base-cased-distilled-squad
+    path: questions
 """
 
 # Configuration for a read-only embeddings index