mem0ai/mem0 · error · ValueError

Invalid docstore value type: {type(value)}, expected dict

Error message

Invalid docstore value type: {type(value)}, expected dict

What it means

Raised while validating docstore entries: a value (the payload) is not a dict. Every docstore entry must map an id to a payload dict (the memory metadata). ValueError raised during FAISS load.

Source

Thrown at mem0/vector_stores/faiss.py:109

        ValueError: If the data structure is invalid.
    """
    if not isinstance(data, tuple) or len(data) != 2:
        raise ValueError("Invalid docstore format: expected tuple of (docstore, index_to_id)")

    docstore, index_to_id = data

    if not isinstance(docstore, dict):
        raise ValueError("Invalid docstore format: docstore must be a dict")

    if not isinstance(index_to_id, dict):
        raise ValueError("Invalid docstore format: index_to_id must be a dict")

    # Validate docstore entries
    for key, value in docstore.items():
        if not isinstance(key, str):
            raise ValueError(f"Invalid docstore key type: {type(key)}, expected str")
        if not isinstance(value, dict):
            raise ValueError(f"Invalid docstore value type: {type(value)}, expected dict")

    # Validate index_to_id entries
    for key, value in index_to_id.items():
        if not isinstance(key, int):
            raise ValueError(f"Invalid index_to_id key type: {type(key)}, expected int")
        if not isinstance(value, str):
            raise ValueError(f"Invalid index_to_id value type: {type(value)}, expected str")

    return docstore, index_to_id


class OutputData(BaseModel):
    id: Optional[str]  # memory id
    score: Optional[float]  # distance
    payload: Optional[Dict]  # metadata


class FAISS(VectorStoreBase):

View on GitHub (pinned to 001c235229)

Solutions

Convert each non-dict payload to a dict (e.g. {'text': doc.page_content, 'metadata': doc.metadata}) in a migration script
Delete and rebuild the store via mem0 add() calls
Validate the file offline with a loop asserting isinstance(v, dict) before constructing FAISS

Example fix

# before
# payload stored as a raw string
# after
payloads = {k: (v if isinstance(v, dict) else {'data': v}) for k, v in docstore.items()}

Defensive patterns

Strategy: validation

Validate before calling

data[0] = {k: (v if isinstance(v, dict) else {'data': v}) for k, v in data[0].items()}

Type guard

def docstore_values_are_dicts(d) -> bool:
    return isinstance(d, dict) and all(isinstance(v, dict) for v in d.values())

Prevention

Store only plain-dict payloads via mem0's add API
Convert foreign Document objects to dicts during migrations

When it happens

Trigger: A persisted docstore where a payload is a string, list, or LangChain Document instead of a dict — typically from converting another framework's FAISS store to mem0's format.

Common situations: Langchain-to-mem0 migrations where Document objects were serialized raw; hand-crafted JSON payloads; partial schema changes between versions.

Related errors

AI-assisted analysis of mem0ai/mem0@001c235229 (2026-08-15). Data as JSON: /api/errors/158fd09a51cf312a. Report an issue: GitHub.