FoundationAgents/MetaGPT · error · ValueError

Field '{self.field_name}' not found in object: {obj_dict}

Error message

Field '{self.field_name}' not found in object: {obj_dict}

What it means

After successfully parsing obj_json, ObjectSortPostprocessor checks that the configured field_name exists in the decoded object dict; if the sort field is absent it raises this ValueError showing the full object. The ranker sorts by metadata[field_name], so a missing field makes sorting impossible.

Source

Thrown at metagpt/rag/rankers/object_ranker.py:52

        if query_bundle is None:
            raise ValueError("Missing query bundle in extra info.")

        if not nodes:
            return []

        self._check_metadata(nodes[0].node)

        sort_key = lambda node: json.loads(node.node.metadata["obj_json"])[self.field_name]
        return self._get_sort_func()(self.top_n, nodes, key=sort_key)

    def _check_metadata(self, node: ObjectNode):
        try:
            obj_dict = json.loads(node.metadata.get("obj_json"))
        except Exception as e:
            raise ValueError(f"Invalid object json in metadata: {node.metadata}, error: {e}")

        if self.field_name not in obj_dict:
            raise ValueError(f"Field '{self.field_name}' not found in object: {obj_dict}")

    def _get_sort_func(self):
        return heapq.nlargest if self.order == "desc" else heapq.nsmallest

View on GitHub (pinned to 11cdf466d0)

Solutions

1. Align field_name with an existing key: inspect json.loads(nodes[0].metadata['obj_json']).keys() and use that key
2. Re-index objects that all contain the sort field, or filter heterogeneous nodes before the ranker
3. Add the field with a default value during ingestion if it is genuinely optional

Example fix

// before
ranker = ObjectSortPostprocessor(field_name="cost", top_n=3)  # objects have "price"

// after
ranker = ObjectSortPostprocessor(field_name="price", top_n=3)

import json
obj = json.loads(nodes[0].node.metadata["obj_json"])
if ranker.field_name not in obj:
    raise ValueError(f"sort field '{ranker.field_name}' not in object keys {sorted(obj)}")

import json

def objects_have_field(nodes, field_name: str) -> bool:
    return all(field_name in json.loads(n.node.metadata.get("obj_json", "{}")) for n in nodes)

try:
    nodes = ranker.postprocess_nodes(nodes, query_bundle=qb)
except ValueError as e:
    if "not found in object" in str(e):
        # inspect keys and rebuild ranker with an existing field
        keys = sorted(json.loads(nodes[0].node.metadata["obj_json"]).keys())
        raise ValueError(f"pick field_name from {keys}") from e
    raise

When it happens

Trigger: Constructing ObjectSortPostprocessor(field_name="price") but the indexed objects' obj_json contains no "price" key; renaming a field in the data model without re-indexing; heterogeneous objects in one index where only some carry the field.

Common situations: Field name typo between the ranker config and the ingested data; schema drift after re-generating objects; mixing object types in a single index.

Related errors

• Invalid object json in metadata: {node.metadata}, error: {e}
• Missing __module_class_name field
• Content column not found in DataFrame.
• File format not supported.
• File {data_path} not found.

AI-assisted analysis of FoundationAgents/MetaGPT@11cdf466d0 (2026-08-14). Data as JSON: /api/errors/b70333a0181067b9. Report an issue: GitHub.