microsoft/autogen · error · NotImplementedError

BaseAzureAISearchTool is an abstract base class and cannot b

Error message

BaseAzureAISearchTool is an abstract base class and cannot be instantiated directly. Use a concrete implementation like AzureAISearchTool.

What it means

_from_config on BaseAzureAISearchTool is a guarded abstract classmethod. If invoked on the base class itself (cls is BaseAzureAISearchTool) it raises NotImplementedError telling you to use a concrete implementation such as AzureAISearchTool. This is a programmer-facing guard for custom subclasses and internal plumbing, not a runtime service error.

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/tools/azure/_ai_search.py:656

        elif search_type == "hybrid":
            vector_fields = config_dict.get("vector_fields")
            search_fields = config_dict.get("search_fields")

            if not vector_fields or len(vector_fields) == 0:
                raise ValueError("vector_fields must contain at least one field name for hybrid search")

            if not search_fields or len(search_fields) == 0:
                raise ValueError("search_fields must contain at least one field name for hybrid search")

    @classmethod
    @abstractmethod
    def _from_config(cls, config: AzureAISearchConfig) -> "BaseAzureAISearchTool":
        """Create a tool instance from a configuration object.

        This is an abstract method that must be implemented by subclasses.
        """
        if cls is BaseAzureAISearchTool:
            raise NotImplementedError(
                "BaseAzureAISearchTool is an abstract base class and cannot be instantiated directly. "
                "Use a concrete implementation like AzureAISearchTool."
            )
        raise NotImplementedError("Subclasses must implement _from_config")

    @abstractmethod
    async def _get_embedding(self, query: str) -> List[float]:
        """Generate embedding vector for the query text."""
        raise NotImplementedError("Subclasses must implement _get_embedding")


_allow_private_constructor = ContextVar("_allow_private_constructor", default=False)


class AzureAISearchTool(EmbeddingProviderMixin, BaseAzureAISearchTool):
    """Azure AI Search tool for querying Azure search indexes.

    This tool provides a simplified interface for querying Azure AI Search indexes using

View on GitHub (pinned to 027ecf0a37)

Solutions

Call the concrete class instead: AzureAISearchTool._from_config(config) (or just use its public factory methods).
In custom subclasses, do not delegate _from_config to super(); construct the concrete instance directly.
If you never extend these classes, this error indicates you are reaching into private API — switch to the documented factory constructors.

Example fix

# before
tool = BaseAzureAISearchTool._from_config(cfg)
# after
tool = AzureAISearchTool._from_config(cfg)

Defensive patterns

Strategy: type-guard

Validate before calling

from autogen_ext.tools.azure._ai_search import BaseAzureAISearchTool, AzureAISearchTool

def is_concrete_tool_cls(cls) -> bool:
    return cls is not BaseAzureAISearchTool

Type guard

def can_from_config(cls) -> bool:
    from autogen_ext.tools.azure._ai_search import BaseAzureAISearchTool
    return cls is not BaseAzureAISearchTool and '_from_config' in cls.__dict__

Try / catch

try:
    tool = cls._from_config(cfg)
except NotImplementedError:
    if cls is BaseAzureAISearchTool:
        cls = AzureAISearchTool  # fall back to the concrete class
        tool = cls._from_config(cfg)
    else:
        raise

Prevention

Never call private _from_config on the base class; use public factory methods.
In generic code, accept only concrete tool classes and assert that at the boundary.
In subclasses, do not delegate _from_config to super().

When it happens

Trigger: Calling BaseAzureAISearchTool._from_config(config) directly, or writing a custom subclass whose _from_config implementation delegates to super()._from_config (which lands on the base implementation).

Common situations: Writing a custom search tool subclass and accidentally calling super()._from_config(config) inside it; generic factory code that receives the base class as a parameter instead of a concrete tool class.

Related errors

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/f214f7572aa622c6. Report an issue: GitHub.