Merge pull request #2329 from langchain-ai/nc/4nov/get-state-apply-pe…

…nding-writes

lib: In calls to get_state apply pending writes

libs/langgraph/langgraph/pregel/__init__.py

@@ -54,6 +54,7 @@
 )
 from langgraph.constants import (
     CONF,
+    CONFIG_KEY_CHECKPOINT_ID,
     CONFIG_KEY_CHECKPOINT_NS,
     CONFIG_KEY_CHECKPOINTER,
     CONFIG_KEY_NODE_FINISHED,
@@ -439,6 +440,7 @@ def _prepare_state_snapshot(
         config: RunnableConfig,
         saved: Optional[CheckpointTuple],
         recurse: Optional[BaseCheckpointSaver] = None,
+        apply_pending_writes: bool = False,
     ) -> StateSnapshot:
         if not saved:
             return StateSnapshot(
@@ -469,7 +471,10 @@ def _prepare_state_snapshot(
                 managed,
                 saved.config,
                 saved.metadata.get("step", -1) + 1,
-                for_execution=False,
+                for_execution=True,
+                store=self.store,
+                checkpointer=self.checkpointer or None,
+                manager=None,
             )
             # get the subgraphs
             subgraphs = dict(self.get_subgraphs())
@@ -503,6 +508,12 @@ def _prepare_state_snapshot(
                     task_states[task.id] = subgraphs[task.name].get_state(
                         config, subgraphs=True
                     )
+            # apply pending writes
+            if apply_pending_writes and saved.pending_writes:
+                for tid, *t in saved.pending_writes:
+                    next_tasks[tid].writes.append(t)  # type: ignore[arg-type]
+                if tasks := [t for t in next_tasks.values() if t.writes]:
+                    apply_writes(saved.checkpoint, channels, tasks, None)
             # assemble the state snapshot
             return StateSnapshot(
                 read_channels(channels, self.stream_channels_asis),
@@ -524,6 +535,7 @@ async def _aprepare_state_snapshot(
         config: RunnableConfig,
         saved: Optional[CheckpointTuple],
         recurse: Optional[BaseCheckpointSaver] = None,
+        apply_pending_writes: bool = False,
     ) -> StateSnapshot:
         if not saved:
             return StateSnapshot(
@@ -557,7 +569,10 @@ async def _aprepare_state_snapshot(
                 managed,
                 saved.config,
                 saved.metadata.get("step", -1) + 1,
-                for_execution=False,
+                for_execution=True,
+                store=self.store,
+                checkpointer=self.checkpointer or None,
+                manager=None,
             )
             # get the subgraphs
             subgraphs = {n: g async for n, g in self.aget_subgraphs()}
@@ -591,6 +606,12 @@ async def _aprepare_state_snapshot(
                     task_states[task.id] = await subgraphs[task.name].aget_state(
                         config, subgraphs=True
                     )
+            # apply pending writes
+            if apply_pending_writes and saved.pending_writes:
+                for tid, *t in saved.pending_writes:
+                    next_tasks[tid].writes.append(t)  # type: ignore[arg-type]
+                if tasks := [t for t in next_tasks.values() if t.writes]:
+                    apply_writes(saved.checkpoint, channels, tasks, None)
             # assemble the state snapshot
             return StateSnapshot(
                 read_channels(channels, self.stream_channels_asis),
@@ -638,7 +659,10 @@ def get_state(
         config = merge_configs(self.config, config) if self.config else config
         saved = checkpointer.get_tuple(config)
         return self._prepare_state_snapshot(
-            config, saved, recurse=checkpointer if subgraphs else None
+            config,
+            saved,
+            recurse=checkpointer if subgraphs else None,
+            apply_pending_writes=CONFIG_KEY_CHECKPOINT_ID not in config[CONF],
         )
 
     async def aget_state(
@@ -672,7 +696,10 @@ async def aget_state(
         config = merge_configs(self.config, config) if self.config else config
         saved = await checkpointer.aget_tuple(config)
         return await self._aprepare_state_snapshot(
-            config, saved, recurse=checkpointer if subgraphs else None
+            config,
+            saved,
+            recurse=checkpointer if subgraphs else None,
+            apply_pending_writes=CONFIG_KEY_CHECKPOINT_ID not in config[CONF],
         )
 
     def get_state_history(

libs/langgraph/tests/test_pregel.py

@@ -1513,9 +1513,10 @@ def reset(self):
     assert two.calls == 2  # two attempts
 
     # latest checkpoint should be before nodes "one", "two"
+    # but we should have applied the write from "one"
     state = graph.get_state(thread1)
     assert state is not None
-    assert state.values == {"value": 1}
+    assert state.values == {"value": 3}
     assert state.next == ("one", "two")
     assert state.tasks == (
         PregelTask(AnyStr(), "one", (PULL, "one"), result={"value": 2}),
@@ -1528,6 +1529,10 @@ def reset(self):
         "writes": None,
         "thread_id": "1",
     }
+    # get_state with checkpoint_id should not apply any pending writes
+    state = graph.get_state(state.config)
+    assert state is not None
+    assert state.values == {"value": 1}
     # should contain pending write of "one"
     checkpoint = checkpointer.get_tuple(thread1)
     assert checkpoint is not None

libs/langgraph/tests/test_pregel_async.py

@@ -482,10 +482,11 @@ async def alittlewhile(input: State) -> None:
         assert awhile.started is False
 
         # checkpoint with output of "alittlewhile" should not be saved
+        # but we should have applied pending writes
         if checkpointer is not None:
             state = await graph.aget_state(thread1)
             assert state is not None
-            assert state.values == {"value": 1}
+            assert state.values == {"value": 3}  # 1 + 2
             assert state.next == (
                 "aparallelwhile",
                 "alittlewhile",
@@ -1722,9 +1723,10 @@ def reset(self):
         assert two.calls == 2
 
         # latest checkpoint should be before nodes "one", "two"
+        # but we should have applied pending writes from "one"
         state = await graph.aget_state(thread1)
         assert state is not None
-        assert state.values == {"value": 1}
+        assert state.values == {"value": 3}
         assert state.next == ("one", "two")
         assert state.tasks == (
             PregelTask(AnyStr(), "one", (PULL, "one"), result={"value": 2}),
@@ -1742,6 +1744,10 @@ def reset(self):
             "writes": None,
             "thread_id": "1",
         }
+        # get_state with checkpoint_id should not apply any pending writes
+        state = await graph.aget_state(state.config)
+        assert state is not None
+        assert state.values == {"value": 1}
         # should contain pending write of "one"
         checkpoint = await checkpointer.aget_tuple(thread1)
         assert checkpoint is not None
@@ -2117,6 +2123,8 @@ async def route_to_three(state) -> Literal["3"]:
         thread1 = {"max_concurrency": 10, "configurable": {"thread_id": "1"}}
 
         assert await graph.ainvoke(["0"], thread1) == ["0", "1"]
+        state = await graph.aget_state(thread1)
+        assert state.values == ["0", "1"]
         assert await graph.ainvoke(None, thread1) == ["0", "1", *range(100), "3"]