fix: joining patterns across expansions BED-7468

[urangel]

Joining expansion pattern steps is updated so that result sets contain path resolutions that satisfy the combined query pattern rather than only a part of a multi step relationship pattern.

The following examples use the active directory sample data as the data source.
Examples:

Inbound multi step relationship pattern with consecutive expansion steps

MATCH p = (t:Base)<-[:MemberOf*1..]-(:Base)<-[:Contains*1..]-()
WHERE COALESCE(t.system_tags, '') CONTAINS 'admin_tier_0'          
RETURN p  
LIMIT 3

Before:

After:

Outbound multi step relationship pattern with consecutive expansion steps

MATCH p = ()-[:Contains*1..]->(:Base)-[:MemberOf*1..]->(t:Base)
WHERE COALESCE(t.system_tags, '') CONTAINS 'admin_tier_0'          
RETURN p  
LIMIT 3

Before:

After:

Inbound multi step relationship pattern with single non-expansion step joined to expansion

MATCH p = (t:Base)<-[:MemberOf]-(:Base)<-[:Contains*1..]-()
WHERE COALESCE(t.system_tags, '') CONTAINS 'admin_tier_0'          
RETURN p  
LIMIT 3

Before:

After:

Outbound multi step relationship pattern with single non-expansion step joined to expansion

MATCH p = ()-[:Contains]->(:Base)-[:MemberOf*1..]->(t:Base)
WHERE COALESCE(t.system_tags, '') CONTAINS 'admin_tier_0'          
RETURN p  
LIMIT 3

Before:

After:

Summary by CodeRabbit

• Refactor
  • Improved internal query translation logic for path traversal and constraint handling.
  • Enhanced consistency in how pattern-based queries are constructed and processed.
  • Updated internal architecture to streamline traversal step handling across multiple query types.

[coderabbitai]

Walkthrough

The changes introduce a new TraversalStepContext struct to encapsulate traversal step information, refactoring method signatures in the pattern translation logic to accept this context wrapper instead of separate parameters. Simultaneously, SQL test translation cases are updated with adjusted alias references and simplified filter conditions across multiple query scenarios.

Changes

Cohort / File(s)	Summary
SQL Test Translation Cases cypher/models/pgsql/test/translation_cases/multipart.sql, cypher/models/pgsql/test/translation_cases/pattern_binding.sql, cypher/models/pgsql/test/translation_cases/pattern_expansion.sql	Adjustments to SQL translation test cases including simplified filters on nodes (removing objectid-based conditions), updated alias consistency in nested CTEs, reworked predicate constraints on node/edge components, and modified join conditions for path root linkage validation.
Pattern Context Type Introduction cypher/models/pgsql/translate/pattern.go	Introduces new TraversalStepContext struct containing PreviousStep, CurrentStep, and IsRootStep fields. Updates method signatures for buildExpansionPattern and buildShortestPathsExpansionPattern to accept context object instead of separate step and flag parameters.
Expansion Method Signature Updates cypher/models/pgsql/translate/expansion.go	Refactors method signatures in buildExpansionPatternRoot, buildExpansionPatternStep, and buildExpansionProjectionConstraints to accept TraversalStepContext. Adds internal step extraction logic and introduces joinCondition computation comparing previous step's frame binding against current step's left node and expansion root ID.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Poem

🐰 A context wraps the steps so neat,
Where previous and current softly meet,
SQL aliases dance in new formation,
Join conditions spring from consolidation!
The patterns bloom with structured grace,
Refactored with a rabbit's embrace! 🌿✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: joining patterns across expansions BED-7468' clearly describes the main change: fixing how pattern joins work across expansion steps in Cypher-to-SQL translation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch BED-7468

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• Generate coding plan for human review comments

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@cypher/models/pgsql/test/translation_cases/multipart.sql`:
- Line 48: The recursive CTE s2 only seeds depth=1 paths from edge e0, so *0..
is missing the zero-length (root = target) case; add a zero-depth seed row to s2
before the existing seed (or union it) that sets root_id = e0.end_id, next_id =
e0.end_id, depth = 0, satisfied based on the same predicate used for the seed
(e.g. (n1.properties ->> 'objectid') like '%-516' and n1.kind_ids @> ...),
is_cycle = false (or true as appropriate), and path = an empty array (array[]
cast to the same id array type) so the recursive walk includes the 0-hop branch.
Reference: modify the s2(...) AS (select ... from edge e0 ...) seed block that
currently creates (e0.end_id, e0.start_id, 1, ...) to also include the
zero-depth union entry.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: d2288301-b1de-4c99-a6df-4a399e1dd1e4

📥 Commits

Reviewing files that changed from the base of the PR and between f97f931 and 4c9ac54.

📒 Files selected for processing (5)

• cypher/models/pgsql/test/translation_cases/multipart.sql
• cypher/models/pgsql/test/translation_cases/pattern_binding.sql
• cypher/models/pgsql/test/translation_cases/pattern_expansion.sql
• cypher/models/pgsql/translate/expansion.go
• cypher/models/pgsql/translate/pattern.go

[zinic]

Good bit of plumbing. Test case changes pass muster. Ship it!