{"record":{"id":"d2b11808bd2210f2","repo":"langchain-ai/langgraph","slug":"cannot-subscribe-to-single-channels-when-other-cha","errorCode":null,"errorMessage":"Cannot subscribe to single channels when other channels are already subscribed to","messagePattern":"Cannot subscribe to single channels when other channels are already subscribed to","errorType":"exception","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"libs/langgraph/langgraph/pregel/main.py","lineNumber":250,"sourceCode":"        self._channels = []\n        self._triggers = []\n        self._tags = []\n        self._metadata = {}\n        self._writes = []\n        self._bound = DEFAULT_BOUND\n        self._retry_policy = []\n        self._cache_policy = None\n        self._timeout = None\n\n    def subscribe_only(\n        self,\n        channel: str,\n    ) -> Self:\n        \"\"\"Subscribe to a single channel.\"\"\"\n        if not self._channels:\n            self._channels = channel\n        else:\n            raise ValueError(\n                \"Cannot subscribe to single channels when other channels are already subscribed to\"\n            )\n\n        self._triggers.append(channel)\n\n        return self\n\n    def subscribe_to(\n        self,\n        *channels: str,\n        read: bool = True,\n    ) -> Self:\n        \"\"\"Add channels to subscribe to.\n\n        Node will be invoked when any of these channels are updated, with a dict of the\n        channel values as input.\n\n        Args:","sourceCodeStart":232,"sourceCodeEnd":268,"githubUrl":"https://github.com/langchain-ai/langgraph/blob/38031739e551638e373fb553453256c23feeb41f/libs/langgraph/langgraph/pregel/main.py#L232-L268","documentation":"Error \"Cannot subscribe to single channels when other channels are already subscribed to\" thrown in langchain-ai/langgraph.","triggerScenarios":"Thrown at libs/langgraph/langgraph/pregel/main.py:250 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"38031739e551638e373fb553453256c23feeb41f","analyzedAt":"2026-08-26T18:02:49.312Z","schemaVersion":2},"datasetVersion":"2026-08-26T21:11:00.512Z"}