{"record":{"id":"95178c2466205b78","repo":"langchain-ai/langgraph","slug":"at-key-self-key-ephemeralvalue-guard-true-ca","errorCode":null,"errorMessage":"At key '{self.key}': EphemeralValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values.","messagePattern":"At key '(.+?)': EphemeralValue\\(guard=True\\) can receive only one value per step\\. Use guard=False if you want to store any one of multiple values\\.","errorType":"exception","errorClass":"InvalidUpdateError","httpStatus":null,"severity":"error","filePath":"libs/langgraph/langgraph/channels/ephemeral_value.py","lineNumber":63,"sourceCode":"        empty.value = self.value\n        return empty\n\n    def from_checkpoint(self, checkpoint: Value) -> Self:\n        empty = self.__class__(self.typ, self.guard)\n        empty.key = self.key\n        if checkpoint is not MISSING:\n            empty.value = checkpoint\n        return empty\n\n    def update(self, values: Sequence[Value]) -> bool:\n        if len(values) == 0:\n            if self.value is not MISSING:\n                self.value = MISSING\n                return True\n            else:\n                return False\n        if len(values) != 1 and self.guard:\n            raise InvalidUpdateError(\n                f\"At key '{self.key}': EphemeralValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values.\"\n            )\n\n        self.value = values[-1]\n        return True\n\n    def get(self) -> Value:\n        if self.value is MISSING:\n            raise EmptyChannelError()\n        return self.value\n\n    def is_available(self) -> bool:\n        return self.value is not MISSING\n\n    def checkpoint(self) -> Value:\n        return self.value\n","sourceCodeStart":45,"sourceCodeEnd":80,"githubUrl":"https://github.com/langchain-ai/langgraph/blob/38031739e551638e373fb553453256c23feeb41f/libs/langgraph/langgraph/channels/ephemeral_value.py#L45-L80","documentation":"Error \"At key '{self.key}': EphemeralValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values.\" thrown in langchain-ai/langgraph.","triggerScenarios":"Thrown at libs/langgraph/langgraph/channels/ephemeral_value.py:63 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"}