Cypher : support Unwind with nested list, fixes #3329

[ExtReMLapin]

Added a single test, cypher test all passes.

Gemini generated fix, PLEASE REVIEW

fixes #3329

[gemini-code-assist]

Summary of Changes

Hello @ExtReMLapin, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request primarily resolves an issue where the Cypher UNWIND clause did not correctly handle nested lists, particularly when used as a standalone operation. The changes involve refining the Cypher execution plan to properly initialize standalone clauses and also include a fix for how relationship directions are interpreted during CREATE and MERGE operations. A dedicated test case has been added to confirm the UNWIND functionality.

Highlights

• Cypher UNWIND Clause Enhancement: The Cypher execution plan has been updated to correctly process standalone UNWIND clauses, allowing them to operate on expressions without requiring a preceding MATCH clause. This specifically addresses the issue of UNWIND with nested lists.
• Relationship Direction Fix in CREATE/MERGE: The logic for creating and merging relationships in both CREATE and MERGE statements has been corrected to properly respect the specified direction of the relationship pattern (e.g., incoming or outgoing edges).
• New Test Case for UNWIND: A new test case, unwindWithNestedList, has been added to validate the fix for UNWIND with nested lists, ensuring accurate counting of elements after multiple unwinding operations.

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Changelog

• engine/src/main/java/com/arcadedb/query/opencypher/executor/CypherExecutionPlan.java
  • Refactored the handling of standalone Cypher clauses (WITH, UNWIND, RETURN) to ensure proper execution plan generation, especially for UNWIND without a preceding MATCH.
• engine/src/main/java/com/arcadedb/query/opencypher/executor/steps/CreateStep.java
  • Added import for Direction enum.
  • Fixed an issue in CREATE statements where relationship direction was not correctly honored when creating edges, ensuring fromVertex and toVertex are assigned based on the relationship's direction.
• engine/src/main/java/com/arcadedb/query/opencypher/executor/steps/MergeStep.java
  • Added import for Direction enum.
  • Fixed an issue in MERGE statements where relationship direction was not correctly honored when merging edges, ensuring fromVertex and toVertex are assigned based on the relationship's direction.
• engine/src/test/java/com/arcadedb/query/opencypher/OpenCypherIssuesTest.java
  • Added a new test file OpenCypherIssuesTest.java.
  • Included unwindWithNestedList test case to verify correct behavior of UNWIND with nested lists, specifically for issue Cypher : UNWIND with nested list is broken WithStep requires a previous step #3329.

Activity

• The author, ExtReMLapin, implemented a fix, noting it was 'Gemini generated'.
• A new test case was added to validate the fix, and all existing Cypher tests passed.
• The author has requested a review for the changes.

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[gemini-code-assist]

Code Review

This pull request provides a solid fix for supporting UNWIND with nested lists by correctly handling standalone UNWIND, WITH, and RETURN clauses. The primary change in CypherExecutionPlan.java is well-designed and robustly addresses the issue by examining the initial clause of the query. Additionally, the changes in CreateStep.java and MergeStep.java to correctly handle relationship directions are a valuable improvement. The new test case in OpenCypherIssuesTest.java is well-written and effectively validates the main fix. Overall, the changes are of high quality and improve the Cypher implementation.

[codecov]

Codecov Report

❌ Patch coverage is 52.17391% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.08%. Comparing base (d6cbc10) to head (a9ad186).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
...query/opencypher/executor/CypherExecutionPlan.java	61.53%	2 Missing and 3 partials ⚠️
...db/query/opencypher/executor/steps/CreateStep.java	40.00%	2 Missing and 1 partial ⚠️
...edb/query/opencypher/executor/steps/MergeStep.java	40.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3354      +/-   ##
==========================================
+ Coverage   56.97%   57.08%   +0.11%     
==========================================
  Files        1368     1368              
  Lines      100624   100632       +8     
  Branches    20490    20494       +4     
==========================================
+ Hits        57326    57443     +117     
+ Misses      34205    34100     -105     
+ Partials     9093     9089       -4     

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[mergify]

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[ExtReMLapin]

oops I just realized it includes my relation direction fix from the other PR

[lvca]

Fixed in simpler way by touching the WithStep only