feat: Add support for multiple outputs in ConditionalRouter (#9271)

* feat: Add support for multiple outputs in ConditionalRouter

* Update haystack/components/routers/conditional_router.py

Co-authored-by: Sebastian Husch Lee <sjrl@users.noreply.github.com>

* add additional route

---------

Co-authored-by: Sebastian Husch Lee <sjrl@users.noreply.github.com>

haystack/components/routers/conditional_router.py

@@ -203,11 +203,19 @@ class ConditionalRouter:
 
         for route in routes:
             # extract inputs
-            route_input_names = self._extract_variables(self._env, [route["output"], route["condition"]])
+            route_input_names = self._extract_variables(
+                self._env,
+                [route["condition"]] + (route["output"] if isinstance(route["output"], list) else [route["output"]]),
+            )
             input_types.update(route_input_names)
 
             # extract outputs
-            output_types.update({route["output_name"]: route["output_type"]})
+            output_names = route["output_name"] if isinstance(route["output_name"], list) else [route["output_name"]]
+            output_types_list = (
+                route["output_type"] if isinstance(route["output_type"], list) else [route["output_type"]]
+            )
+
+            output_types.update(dict(zip(output_names, output_types_list)))
 
         # remove optional variables from mandatory input types
         mandatory_input_types = input_types - set(self.optional_variables)
@@ -306,27 +314,45 @@ class ConditionalRouter:
                     rendered = ast.literal_eval(rendered)
                 if not rendered:
                     continue
-                # We now evaluate the `output` expression to determine the route output
-                t_output = self._env.from_string(route["output"])
-                output = t_output.render(**kwargs)
-                # We suppress the exception in case the output is already a string, otherwise
-                # we try to evaluate it and would fail.
-                # This must be done cause the output could be different literal structures.
-                # This doesn't support any user types.
-                with contextlib.suppress(Exception):
-                    if not self._unsafe:
-                        output = ast.literal_eval(output)
+
+                # Handle multiple outputs
+                outputs = route["output"] if isinstance(route["output"], list) else [route["output"]]
+                output_types = (
+                    route["output_type"] if isinstance(route["output_type"], list) else [route["output_type"]]
+                )
+                output_names = (
+                    route["output_name"] if isinstance(route["output_name"], list) else [route["output_name"]]
+                )
+
+                result = {}
+                for output, output_type, output_name in zip(outputs, output_types, output_names):
+                    # Evaluate output template
+                    t_output = self._env.from_string(output)
+                    output_value = t_output.render(**kwargs)
+
+                    # We suppress the exception in case the output is already a string, otherwise
+                    # we try to evaluate it and would fail.
+                    # This must be done cause the output could be different literal structures.
+                    # This doesn't support any user types.
+                    with contextlib.suppress(Exception):
+                        if not self._unsafe:
+                            output_value = ast.literal_eval(output_value)
+
+                    # Validate output type if needed
+                    if self._validate_output_type and not self._output_matches_type(output_value, output_type):
+                        raise ValueError(f"Route '{output_name}' type doesn't match expected type")
+
+                    result[output_name] = output_value
+
+                return result
+
             except Exception as e:
+                # If this was a type‐validation failure, let it propagate as a ValueError
+                if isinstance(e, ValueError):
+                    raise
                 msg = f"Error evaluating condition for route '{route}': {e}"
                 raise RouteConditionException(msg) from e
 
-            if self._validate_output_type and not self._output_matches_type(output, route["output_type"]):
-                msg = f"""Route '{route["output_name"]}' type doesn't match expected type"""
-                raise ValueError(msg)
-
-            # and return the output as a dictionary under the output_name key
-            return {route["output_name"]: output}
-
         raise NoRouteSelectedException(f"No route fired. Routes: {self.routes}")
 
     def _validate_routes(self, routes: List[Dict]):
@@ -347,9 +373,23 @@ class ConditionalRouter:
                 raise ValueError(
                     f"Route must contain 'condition', 'output', 'output_type' and 'output_name' fields: {route}"
                 )
-            for field in ["condition", "output"]:
-                if not self._validate_template(self._env, route[field]):
-                    raise ValueError(f"Invalid template for field '{field}': {route[field]}")
+
+            # Validate outputs are consistent
+            outputs = route["output"] if isinstance(route["output"], list) else [route["output"]]
+            output_types = route["output_type"] if isinstance(route["output_type"], list) else [route["output_type"]]
+            output_names = route["output_name"] if isinstance(route["output_name"], list) else [route["output_name"]]
+
+            # Check lengths match
+            if not len(outputs) == len(output_types) == len(output_names):
+                raise ValueError(f"Route output, output_type and output_name must have same length: {route}")
+
+            # Validate templates
+            if not self._validate_template(self._env, route["condition"]):
+                raise ValueError(f"Invalid template for condition: {route['condition']}")
+
+            for output in outputs:
+                if not self._validate_template(self._env, output):
+                    raise ValueError(f"Invalid template for output: {output}")
 
     def _extract_variables(self, env: Environment, templates: List[str]) -> Set[str]:
         """

releasenotes/notes/multiple-outputs-conditional-router-c2f0caad3d3f8ce5.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - |
+    Add support for multiple outputs in ConditionalRouter

test/components/routers/test_conditional_router.py

@@ -574,3 +574,44 @@ class TestRouter:
         assert new_router.routes == router.routes
         assert new_router.routes[0]["output_type"] is str
         assert new_router.routes[0]["output_type"] is original_output_type
+
+    def test_multiple_outputs_per_route(self):
+        """Test that router handles multiple outputs per route correctly"""
+        routes = [
+            {
+                "condition": "{{streams|length >= 2}}",
+                "output": ["{{streams}}", "{{query}}"],
+                "output_type": [List[int], str],
+                "output_name": ["streams", "query"],
+            },
+            {
+                "condition": "{{streams|length < 2}}",
+                "output": ["{{streams}}", "{{custom_error_message}}"],
+                "output_type": [List[int], str],
+                "output_name": ["streams", "custom_error_message"],
+            },
+        ]
+        router = ConditionalRouter(routes)
+
+        # Test with sufficient input streams
+        result = router.run(streams=[1, 2, 3], query="test_1", custom_error_message="Not enough streams")
+        assert result == {"streams": [1, 2, 3], "query": "test_1"}
+
+        # Test with insufficient input streams
+        result = router.run(streams=[1], query="test_2", custom_error_message="Not enough streams")
+        assert result == {"streams": [1], "custom_error_message": "Not enough streams"}
+
+    def test_multiple_outputs_validation(self):
+        """Test validation of routes with multiple outputs"""
+        # Test mismatched lengths
+        with pytest.raises(ValueError, match="must have same length"):
+            ConditionalRouter(
+                [
+                    {
+                        "condition": "{{streams|length >= 2}}",
+                        "output": ["{{streams}}", "{{query}}"],
+                        "output_type": [List[int]],
+                        "output_name": ["streams"],
+                    }
+                ]
+            )