agentscope-ai/agentscope · error · ValueError

"Mem0Middleware needs one of: a pre-built `client`, a `mem0_

Error message

"Mem0Middleware needs one of: a pre-built `client`, a `mem0_config`, or both `chat_model` and `embedding_model`."

What it means

_resolve_client builds or accepts a mem0 AsyncMemory client; when no client, no mem0_config, and no models are supplied there is no way to construct one, so construction fails with this error listing the three accepted paths.

Source

Thrown at src/agentscope/middleware/_longterm_memory/_mem0/_middleware.py:455

                    ("chat_model", chat_model),
                    ("embedding_model", embedding_model),
                    ("mem0_config", mem0_config),
                )
                if value is not None
            ]
            if ignored:
                logger.warning(
                    "Mem0Middleware: `client` was provided, so %s "
                    "%s ignored. Pass them via the mem0 client itself "
                    "(or omit `client` to let the middleware build one "
                    "for you).",
                    ", ".join(ignored),
                    "is" if len(ignored) == 1 else "are",
                )
        if client is None:
            no_models = chat_model is None and embedding_model is None
            if mem0_config is None and no_models:
                raise ValueError(
                    "Mem0Middleware needs one of: a pre-built `client`, "
                    "a `mem0_config`, or both `chat_model` and "
                    "`embedding_model`.",
                )
            # When no mem0_config is given, models must come as a pair.
            if mem0_config is None and (
                (chat_model is None) ^ (embedding_model is None)
            ):
                raise ValueError(
                    "Mem0Middleware: `chat_model` and "
                    "`embedding_model` must be passed together when "
                    "`mem0_config` is not given.",
                )

            from mem0 import AsyncMemory

            from ._agentscope_adapter import build_mem0_config

View on GitHub (pinned to e90f1c7592)

Solutions

Pass chat_model= and embedding_model= (an AgentScope ChatModelBase and EmbeddingModelBase)
Or pass mem0_config=dict with full llm/embedder/vector_store blocks
Or pass a pre-built mem0.AsyncMemory as client=

Example fix

// before
mw = Mem0Middleware(user_id='u1')
// after
mw = Mem0Middleware(user_id='u1', chat_model=chat, embedding_model=emb)

Defensive patterns

Strategy: validation

Validate before calling

if client is None and mem0_config is None and (chat_model is None or embedding_model is None):
    raise ValueError('need client, mem0_config, or both chat_model and embedding_model')

Try / catch

try:
    mw = Mem0Middleware(user_id='u1')
except ValueError as e:
    if 'needs one of' in str(e):
        mw = Mem0Middleware(user_id='u1', chat_model=c, embedding_model=e)
    else:
        raise

Prevention

Centralize middleware construction in one factory that always passes models or client

When it happens

Trigger: Mem0Middleware(user_id='u1') with no client, mem0_config, chat_model, or embedding_model arguments.

Common situations: Assuming mem0 falls back to environment variables (it doesn't through this path); forgetting wiring in quick-start code.

Related errors

AI-assisted analysis of agentscope-ai/agentscope@e90f1c7592 (2026-08-28). Data as JSON: /api/errors/84dad28965d5e504. Report an issue: GitHub.