Phase 3: Search API — KNN, RRF, field projection, groupBy, read levels

[oss-amikos]

Summary

Phase 3: Search API
Goal: Implement the Chroma Search endpoint (v1.5+) with full ranking expression DSL, field projection, groupBy, and read levels — matching Go client capabilities.
Status: Verified ✓ (8/8 must-haves)

Implements the complete Search API for the v2 Java client. Users can execute collection.search().queryText("foo").limit(5).execute() to perform KNN search, compose RRF from multiple weighted rankings, project specific fields via Select, group results by metadata key, and control read levels. The implementation follows the established v2 patterns (immutable value objects, fluent builders, defensive copies, interface-first design).

Changes

Plan 03-01: Search API Type System

Search API value types and builder interfaces — the complete type contracts.

Key files created:

• SparseVector.java — immutable sparse vector value type with defensive copies
• Select.java — field projection constants (DOCUMENT, SCORE, EMBEDDING, METADATA, ID) and key() factory
• ReadLevel.java — INDEX_AND_WAL / INDEX_ONLY enum
• GroupBy.java — builder with required key and optional minK/maxK
• Knn.java — factory+fluent-chain ranking expression (queryText, queryEmbedding, querySparseVector)
• Rrf.java — RRF builder combining multiple KNN sub-rankings with weights
• Search.java — per-search builder composing rank, filter, select, groupBy, limit, offset
• SearchResult.java / SearchResultRow.java / SearchResultGroup.java — result interfaces
• Collection.java — added SearchBuilder search() and SearchBuilder inner interface

Plan 03-02: HTTP Pipeline

DTOs, serialization, and ChromaHttpCollection wiring.

Key files created/modified:

• ChromaDtos.java — SearchRequest/SearchResponse DTOs, buildKnnRankMap/buildRrfRankMap/buildSearchItemMap helpers
• ChromaApiPaths.java — collectionSearch() path builder
• SearchResultImpl.java — immutable result with lazy-cached rows via AtomicReferenceArray
• SearchResultRowImpl.java — composition over ResultRowImpl with Double score
• SearchResultGroupImpl.java — group key + row group
• ChromaHttpCollection.java — SearchBuilderImpl with convenience methods, batch support, global filter/limit/offset, readLevel

Plan 03-03: Tests

Comprehensive unit and integration test suite.

Key files created/modified:

• SparseVectorTest.java — 8 tests (immutability, validation, defensive copies)
• SelectTest.java — 7 tests (constants, factory, equality)
• SearchApiUnitTest.java — 65 tests (KNN/RRF/Search builders, DTO wire format, null validation, result parsing, bounds checks)
• SearchApiPropertyTest.java — 9 property-based tests using QuickTheories (roundtrip precision, immutability, constraint validation)
• SearchApiIntegrationTest.java — 12 cloud-gated integration tests (KNN, batch, RRF, projection, ReadLevel, GroupBy, filters)
• PublicInterfaceCompatibilityTest.java — updated to EXPECTED_COLLECTION_METHOD_COUNT=22

Post-review fixes

• Fixed 25 code review findings (null validation, defensive copies, score precision, contract consistency)
• Extracted ImmutableCopyUtils (eliminated ~100 lines of duplication between QueryResultImpl/SearchResultImpl)
• Added Search.toBuilder() for safe field copying

Requirements Addressed

• SEARCH-01: KNN embedding search with queryText, queryEmbedding, querySparseVector
• SEARCH-02: RRF (Reciprocal Rank Fusion) from multiple weighted rank expressions
• SEARCH-03: Field projection via Select constants and custom metadata key projection
• SEARCH-04: GroupBy metadata key with min/max K controls, ReadLevel enum

Verification

• Automated verification: 8/8 must-haves passed
• 144 unit + property tests passing
• Java 8 compatibility confirmed (animal-sniffer)
• Wire format validated: $knn/$rrf prefixed keys match Chroma >= 1.5
• Human verification: RRF execution (server doesn't support $rrf yet)
• Human verification: Text queryText execution (server rejects string $knn.query)
• Human verification: GroupBy key extraction (server grouped response format TBD)

Key Decisions

• Score type is Double (not Float) to preserve wire-format precision end-to-end
• SearchResultRow.getScore() returns Double for consistency with SearchResult.getScores()
• groups() throws IllegalStateException when not grouped (fail-fast for caller mistakes)
• groupCount() renamed to searchCount() to avoid confusion with GroupBy semantics
• Text queries sent to server verbatim (server-side embedding, unlike client-side QueryBuilder)
• Wire format uses $knn/$rrf prefixed keys (discovered during integration testing)
• QuickTheories 0.26 added for property-based testing (Java 8 + JUnit 4 compatible)

Test Plan

• mvn test -Dtest=SparseVectorTest,SelectTest,SearchApiUnitTest,SearchApiPropertyTest,PublicInterfaceCompatibilityTest — all 144 tests pass
• mvn compile with animal-sniffer — Java 8 compatible
• mvn test -Dtest=SearchApiIntegrationTest — requires Docker with Chroma >= 1.5
• mvn test -Dtest=SearchApiCloudIntegrationTest — requires CHROMA_API_KEY

[tazarov]

@claude PTAL

[claude]

Claude finished @tazarov's task in 3m 7s —— View job

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Code Review: Phase 3 — Search API

• Gather context and understand the PR
• Review core value types (SparseVector, Select, ReadLevel, GroupBy)
• Review ranking expressions (Knn, Rrf, Search)
• Review HTTP pipeline (DTOs, ChromaHttpCollection)
• Review result types and utilities
• Review Collection interface changes
• Review tests

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Overall this is a well-structured, thorough implementation. The immutable value types, defensive copies, and fluent builder APIs are consistent with the v2 patterns established earlier. Good test coverage at 144+ tests across unit, property-based, and integration layers. Below are the findings organized by severity.

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Issues

1. Search.Builder.select() doesn't make a defensive copy of the varargs array

File: Search.java:181

public Builder select(Select... fields) {
    Objects.requireNonNull(fields, "fields must not be null");
    for (int i = 0; i < fields.length; i++) {
        if (fields[i] == null) {
            throw new IllegalArgumentException("fields[" + i + "] must not be null");
        }
    }
    this.select = fields; // ← caller can mutate after passing
}

The varargs array is stored directly without Arrays.copyOf(). After calling builder.select(a, b), the caller still holds a reference to the backing array and could mutate it before build() is called. Every other mutable input in this PR gets defensively copied — this one should too.

Fix this →

2. SearchBuilderImpl.execute() — global offset applied inconsistently

File: ChromaHttpCollection.java:1023-1029

if (s.getLimit() == null && (globalLimit != null || globalOffset != null)) {
    int effectiveOffset = s.getOffset() != null ? s.getOffset()
            : (globalOffset != null ? globalOffset : 0);
    Search.Builder b = s.toBuilder();
    if (globalLimit != null) b.limit(globalLimit);
    b.offset(effectiveOffset);
    effectiveSearches.add(b.build());
}

The condition gates on s.getLimit() == null, meaning if a Search already has its own limit set but no offset, and a global offset is configured, that global offset is silently ignored. The Javadoc says "default result offset applied to individual searches that do not specify their own offset" — this should apply regardless of whether the search has its own limit. Consider checking limit and offset independently.

Fix this →

3. SearchResultImpl.groups() is a placeholder — should document or throw UnsupportedOperationException

File: SearchResultImpl.java:127-147

The groups() method currently wraps each row in a single-element group with key=null. The TODO comment acknowledges this, but callers won't know they're getting stub behavior. Consider either:

• Throwing UnsupportedOperationException("GroupBy response parsing not yet implemented") so callers fail fast, or
• Documenting this as provisional behavior in the SearchResult.groups() Javadoc

Currently, callers get silently wrong results — each "group" contains exactly one row with a null key, which defeats the purpose of grouping.

4. Knn.limit() accepts zero and negative values without validation

File: Knn.java:106-108

public Knn limit(int limit) {
    return new Knn(this.query, this.key, limit, this.defaultScore, this.returnRank);
}

Unlike SearchBuilder.limit() which validates > 0, Knn.limit() accepts any int including 0 and negative values. For consistency and fail-fast behavior, consider adding if (limit <= 0) throw new IllegalArgumentException(...).

Fix this →

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Nits / Minor Suggestions

5. Select.all() returns a new array on every call

File: Select.java:57-59

public static Select[] all() {
    return new Select[]{ID, DOCUMENT, EMBEDDING, METADATA, SCORE};
}

This allocates a new array each time. Could cache it as a private static field and return a copy, or just leave as-is since it's cheap. Very minor.

6. Knn stores query as Object — type safety

File: Knn.java:24

The query field is Object, holding either String, float[], or SparseVector. This works but means the type contract is enforced only by the factory methods. A tagged-union or visitor pattern would be more type-safe, but I understand this is a pragmatic choice for Java 8 compatibility. Just noting it.

7. ReadLevel.fromValue() uses toLowerCase(Locale.ROOT) but enum values are already lowercase

File: ReadLevel.java:43

The normalization handles case-insensitive input, which is good for robustness. The test at line 644 confirms this works for "INDEX_AND_WAL" — nice.

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What Looks Good

• Immutability discipline is excellent throughout. SparseVector, GroupBy, Knn, Rrf, Search are all properly immutable with defensive copies.
• ImmutableCopyUtils extraction eliminates duplication between QueryResultImpl and SearchResultImpl cleanly.
• Wire format ($knn/$rrf prefixed keys) is well-encapsulated in ChromaDtos with clear serialization helpers.
• Search.toBuilder() is a nice addition for the effective-search-list logic in SearchBuilderImpl.
• Builder validation is thorough — mutual exclusion of knn/rrf, null checks, range checks on GroupBy min/max K.
• AtomicReferenceArray lazy caching pattern in SearchResultImpl is correctly thread-safe.
• Test coverage is comprehensive — 65 unit tests for wire format, 9 property tests with QuickTheories, integration tests for cloud and self-hosted.
• Java 8 compatibility maintained throughout (no diamond operators on anonymous classes, no newer APIs).

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Summary

The implementation is solid and production-ready. The main actionable items are:

#	Severity	Issue
1	Medium	Missing defensive copy in Search.Builder.select()
2	Medium	Global offset not applied when per-search limit exists
3	Low	groups() silently returns stub data
4	Low	Knn.limit() missing bounds validation

Items 1-2 are worth fixing before merge. Items 3-4 are lower priority but would improve API robustness.

[tazarov]

@claude PTAL again

[claude]

Claude finished @tazarov's task in 2m 29s —— View job

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Re-review: Phase 3 — Search API

• Check if previous review findings were addressed
• Review any new changes since last review
• Provide updated review feedback

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Previous Findings — All Addressed

#	Finding	Status
1	Missing defensive copy in Search.Builder.select()	Fixed — now uses Arrays.copyOf() (Search.java:181)
2	Global offset not applied when per-search limit exists	Fixed — limit and offset now checked independently (ChromaHttpCollection.java:1023-1029)
3	groups() silently returns stub data	Fixed — now throws IllegalStateException when not grouped, with clear TODO for server format (SearchResultImpl.java:130-133)
4	Knn.limit() missing bounds validation	Fixed — now validates limit > 0 (Knn.java:107-109)

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Fresh Review — Remaining Items

After a thorough re-review of all 17 core files, the implementation is in good shape. No high-severity issues found. A few minor items remain:

1. SearchBuilderImpl.searches() — Arrays.asList backed by input array (Low)

File: ChromaHttpCollection.java:979

this.searches = Arrays.asList(searches);

Arrays.asList() returns a list backed by the original array. For varargs this is safe in practice (the compiler creates a fresh array), but it's inconsistent with the defensive copy discipline used everywhere else. A new ArrayList<>(Arrays.asList(searches)) would be more robust.

2. GroupBy result parsing is a documented placeholder (Low)

File: SearchResultImpl.java:135-147

The groups() method wraps each row in a single-element group with key=null. This is documented with a TODO and gated behind isGrouped() + IllegalStateException, which is the right approach given the server response format is TBD. No action needed now — just noting it's still provisional.

3. Double cast in Knn.getQuery() (Nit)

File: Knn.java:150-155

if (query instanceof float[]) {
    return Arrays.copyOf((float[]) query, ((float[]) query).length);
}

The array is cast twice. Could cache the cast: float[] arr = (float[]) query; return Arrays.copyOf(arr, arr.length);. Purely cosmetic.

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What Looks Good

• All 4 previous findings cleanly addressed in commit 1ba9b25
• Immutability discipline remains excellent — defensive copies, unmodifiable collections throughout
• Thread safety in SearchResultImpl via AtomicReferenceArray lazy caching is correct
• ImmutableCopyUtils extraction cleanly eliminates duplication between QueryResultImpl/SearchResultImpl
• Wire format ($knn/$rrf prefixed keys) well-encapsulated in ChromaDtos
• Builder validation is thorough — mutual exclusion, null checks, range checks
• Test coverage is comprehensive at 144+ tests across unit, property-based, and integration layers
• Java 8 compatibility maintained throughout

Verdict

The code is ready to merge. The remaining items are minor and can be addressed in follow-up work if desired. Nice implementation.

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[tazarov]

@claude PTAL

[claude]

Claude finished @tazarov's task in 2m 22s —— View job

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Re-review: Phase 3 — Search API (Round 3)

• Check changes since last review
• Review core implementation files
• Review test coverage
• Provide final assessment

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Changes Since Last Review

Commit 8870bff removed groups()/isGrouped() from SearchResult entirely — along with SearchResultGroup and SearchResultGroupImpl. This directly addresses finding #3 from the previous review. Good call removing the placeholder rather than keeping stub behavior that silently returns wrong results. The GroupBy functionality can be added properly when the server response format is finalized.

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Previous Findings Status

#	Finding	Status
1	Missing defensive copy in Search.Builder.select()	Fixed ✓
2	Global offset not applied when per-search limit exists	Fixed ✓
3	groups() silently returns stub data	Removed entirely ✓ (best outcome)
4	Knn.limit() missing bounds validation	Fixed ✓
5	searches() backed by Arrays.asList	Still present (see below)
6	Double cast in Knn.getQuery()	Still present (cosmetic)

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Remaining Items

1. SearchBuilderImpl.searches() — Arrays.asList backed by input array (Low)

File: ChromaHttpCollection.java:979

this.searches = Arrays.asList(searches);

Arrays.asList() returns a list backed by the original array. For varargs this is safe in practice (compiler creates a fresh array), but it's inconsistent with the defensive-copy discipline used everywhere else. A new ArrayList<>(Arrays.asList(searches)) would be more robust.

2. Double cast in Knn.getQuery() (Nit)

File: Knn.java:151-153

return Arrays.copyOf((float[]) query, ((float[]) query).length);

Cast twice; could cache: float[] arr = (float[]) query; return Arrays.copyOf(arr, arr.length);.

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What Looks Good

• All 4 original findings addressed, plus the placeholder groups() API cleanly removed rather than left as a stub
• Immutability is thorough — ImmutableCopyUtils deep-copies all nested structures (lists, maps, float arrays) correctly
• Thread safety in SearchResultImpl via AtomicReferenceArray + compareAndSet is correct
• Global limit/offset now applied independently as fallbacks — the refactored logic at ChromaHttpCollection.java:1020-1031 is clean
• Wire format ($knn/$rrf prefixed keys) well-encapsulated in ChromaDtos
• Builder validation is thorough — mutual exclusion, null checks, range checks
• Test coverage is comprehensive at 130+ tests across unit, property-based, and integration layers
• Java 8 compatibility maintained throughout

Verdict

The code is ready to merge. All previous findings have been addressed cleanly. The two remaining items are minor nits that don't affect correctness. Nice work on the implementation.

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