quality of life function to access certain nodes in pipeline (#1441)

haystack/pipeline.py

@@ -33,10 +33,7 @@
 from haystack.retriever.base import BaseRetriever
 from haystack.summarizer.base import BaseSummarizer
 from haystack.translator.base import BaseTranslator
-from haystack.knowledge_graph.base import BaseKnowledgeGraph
-from haystack.graph_retriever.base import BaseGraphRetriever
-from haystack.connector import Crawler
-
+from haystack.document_store.base import BaseDocumentStore
 
 logger = logging.getLogger(__name__)
 
@@ -329,6 +326,37 @@ def get_next_nodes(self, node_id: str, stream_id: str):
         ]
         return next_nodes
 
+    def get_nodes_by_class(self, class_type) -> List[Any]:
+        """
+        Gets all nodes in the pipeline that are an instance of a certain class (incl. subclasses).
+        This is for example helpful if you loaded a pipeline and then want to interact directly with the document store.
+        Example:
+        | from haystack.document_store.base import BaseDocumentStore
+        | INDEXING_PIPELINE = Pipeline.load_from_yaml(Path(PIPELINE_YAML_PATH), pipeline_name=INDEXING_PIPELINE_NAME)
+        | res = INDEXING_PIPELINE.get_nodes_by_class(class_type=BaseDocumentStore)
+
+        :return: List of components that are an instance the requested class
+        """
+
+        matches = [self.graph.nodes.get(node)["component"]
+                   for node in self.graph.nodes
+                   if isinstance(self.graph.nodes.get(node)["component"], class_type)]
+        return matches
+
+    def get_document_store(self) -> Optional[BaseDocumentStore]:
+        """
+        Return the document store object used in the current pipeline.
+
+        :return: Instance of DocumentStore or None
+        """
+        matches = self.get_nodes_by_class(class_type=BaseDocumentStore)
+        if len(matches) > 1:
+            raise Exception(f"Multiple Document Stores found in Pipeline: {matches}")
+        elif len(matches) == 0:
+            return None
+        else:
+            return matches[0]
+
     def draw(self, path: Path = Path("pipeline.png")):
         """
         Create a Graphviz visualization of the pipeline.