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ragflow/rag/utils
cleanjunc 88e4d6bddb Fix: restore GraphRAG entity ranking by indexing pagerank and n-hop paths (#15797)
### Summary

Closes #15795 

Knowledge-graph queries rank entities by `pagerank * sim` in `KGSearch`,
but the entity chunks written at index time stopped carrying the values
that ranking depends on. `graph_node_to_chunk` only stored
`entity_type`, `description`, and `source_id`, dropping the node
`pagerank` and the n-hop neighbour paths, while `search.py` still read
them back as `rank_flt` and `n_hop_with_weight`.

The producer of these fields, `update_nodes_pagerank_nhop_neighbour`,
was removed in #6513, but the read side in `KGSearch` was never updated.
The result is that on every knowledge-graph query:

- `pagerank` resolves to `0`, so the `pagerank * sim` sort key is `0`
for every entity and selection falls back to arbitrary order.
- Every displayed entity score is `0.00`.
- The n-hop relation-enrichment block is dead code because `n_hop_ents`
is always empty, leaving `merge_tuples` and `is_continuous_subsequence`
orphaned.

This PR restores the missing index-time fields so the documented `P(E|Q)
= pagerank * sim` ranking and the n-hop enrichment work again.

What changed:

- `graph_node_to_chunk` now writes `rank_flt` from the node pagerank and
`n_hop_with_weight` from the recomputed n-hop neighbour paths.
- Reintroduced the n-hop path computation (`n_neighbor`) in
`rag/graphrag/utils.py`, reusing the previously orphaned `merge_tuples`
/ `is_continuous_subsequence` helpers, with a direction-agnostic
edge-weight lookup for undirected graphs. `set_graph` computes the paths
per added or updated node and passes them through.
- `KGSearch` now selects `n_hop_with_weight` in the entity keyword
search so Infinity and OceanBase return it (Elasticsearch and OpenSearch
already read it from `_source`), and the read is hardened against
missing keys or empty strings before `json.loads`.
- Added the `n_hop_with_weight` column to OceanBase, including the
`EXTRA_COLUMNS` migration entry so existing tables get it. The other
engines already map both fields via dynamic templates or the Infinity
mapping.

Scope note: pagerank and n-hop are re-indexed for the added or updated
nodes in each pass, consistent with the existing incremental indexing
design.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

### Testing

Added unit tests in
`test/unit_test/rag/graphrag/test_graphrag_utils.py`:

- `n_neighbor`: path and weight shape, one-hop vs two-hop, isolated
nodes, missing weights, and direction-agnostic lookup.
- `graph_node_to_chunk`: `rank_flt` populated from pagerank and
defaulting to `0`, `n_hop_with_weight` serialized and defaulting to an
empty list.

```
uv run pytest test/unit_test/rag/graphrag/   # 106 passed
uv run ruff check rag/graphrag/ rag/utils/ob_conn.py
```
2026-06-09 20:50:45 +08:00
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