Fix: Allow non-score sorts in pinned retriever sub-retrievers

[mridula-s109]

Summary

Fixes an issue where the pinned retriever was too restrictive with sort criteria in sub-retrievers, only allowing score-based sorting. This change allows custom sort criteria while maintaining the pinned document functionality.

Changes

• Modified validateSort in PinnedRetrieverBuilder to only check the first sort criterion
• Added test case to verify pinned retriever works with custom sort criteria
• Fixed code style issues

Testing

• All unit tests pass
• YAML REST tests pass
• Manually verified pinned retriever works with custom sorts

Notes

• The pinned document will still appear first in results
• Additional sort criteria are now allowed after the first score-based sort

Test Results

Tested with the following query:

GET books/_search
{
  "retriever": {
    "pinned": {
      "retriever": {
        "standard": {
          "query": {
            "multi_match": {
              "query": "alien"
            }
          },
          "sort": [
            { "_score": "desc" },
            { "publication_year": "desc" }
          ]
        }
      },
      "docs": [
        { "_id": "1", "_index": "books" }
      ]
    }
  }
}

Response:

{
  "took": 3,
  "hits": {
    "total": { "value": 2, "relation": "eq" },
    "max_score": 1.7014122e+38,
    "hits": [
      {
        "_id": "1",
        "_score": 1.7014122e+38,
        "_source": {
          "title": "Neuromancer",
          "author": "William Gibson",
          "publication_year": 1984,
          "genre": "science_fiction"
        }
      },
      {
        "_id": "3",
        "_score": 0.7590337,
        "_source": {
          "title": "Alien: River of Pain",
          "author": "Tim Lebbon",
          "publication_year": 2014,
          "genre": "science_fiction"
        }
      }
    ]
  }
}

[Copilot]

Pull Request Overview

This PR relaxes the pinned retriever's sort criteria by allowing additional non-score sort fields after ensuring that the first sort criterion remains score-based. Key changes include modifying the sort validation logic in PinnedRetrieverBuilder and updating the associated tests to confirm the behavior.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
x-pack/plugin/search-business-rules/src/main/java/org/elasticsearch/xpack/searchbusinessrules/retriever/PinnedRetrieverBuilder.java	Updated sort validation to only check that the first sort is score-based
x-pack/plugin/search-business-rules/src/test/java/org/elasticsearch/xpack/searchbusinessrules/retriever/PinnedRetrieverBuilderTests.java	Adjusted tests to account for the new validated behavior and added assertions to verify sort order

[elasticsearchmachine]

Pinging @elastic/search-eng (Team:SearchOrg)

[elasticsearchmachine]

Pinging @elastic/search-relevance (Team:Search - Relevance)

[elasticsearchmachine]

Hi @mridula-s109, I've created a changelog YAML for you.

[kderusso]

Changes LGTM.

This is a good bugfix to have, but note that this doesn't get at what we were hoping for - which was the ability to pin a single document at the top of an otherwise sorted list of results (think, pinning a result at the top of a result set that's otherwise sorted by publication date). Looking into it it's a larger issue to support that because it's a fundamental limitation of the pinned query DSL, which the retriever defers to. More advanced sub-sorting options would be a (non trivial) enhancement request CC: @serenachou

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[Copilot]

Pull Request Overview

This PR updates the pinned retriever to only enforce score-based sorting on the first criterion, allowing additional custom sorts thereafter.

• Only the first sort is validated to be by _score
• Test added to verify multiple-sort support
• Changelog entry for the bug fix

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
x-pack/plugin/search-business-rules/src/main/java/org/elasticsearch/xpack/searchbusinessrules/retriever/PinnedRetrieverBuilder.java	Simplified validateSort to only check the first sort criterion
x-pack/plugin/search-business-rules/src/test/java/org/elasticsearch/xpack/searchbusinessrules/retriever/PinnedRetrieverBuilderTests.java	Updated tests to allow custom secondary sorts and assert their presence
docs/changelog/128323.yaml	Added changelog entry for non-score secondary sort support

Comments suppressed due to low confidence (1)

x-pack/plugin/search-business-rules/src/test/java/org/elasticsearch/xpack/searchbusinessrules/retriever/PinnedRetrieverBuilderTests.java:223

• Add a test case where the first sort is the pinned-docs sort field (ShardDocSortField.NAME) followed by _score to ensure that validateSort allows the injected shard-doc sort.

e = expectThrows(IllegalArgumentException.class, () -> builder.finalizeSourceBuilder(fieldFirstSource));

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	8.19