[ShryukGrandhi]

Purpose of the PR

• Fixes [Store] LIMIT_DEDUP on NO_SCAN with loadPropertyFromIndex compares BaseVertex by reference #3443

In BusinessHandlerImpl.scanIndex(...), the transElement branch wraps scanIndexToBaseElement in MapLimitIterator for LIMIT_DEDUP. MapLimitIterator dedups on the elements themselves, but BaseVertex and BaseElement don't define equals/hashCode, so two vertex objects with the same id both get through. DEDUP and PRECISE_DEDUP on the same branch already dedup by id.

The path isn't reachable yet (index2Element throws and loadPropertyFromIndex is always false), but once it is, any index that writes several entries per element (search, collection secondary, joint secondary) would return the same vertex more than once.

Main Changes

• MapLimitIterator gets a second constructor that takes a key extractor; the existing constructor uses Function.identity(), so the BackendColumn callers behave as before.
• The LIMIT_DEDUP case on the transElement path passes BaseElement::id.
• BaseVertex equality is left alone, since changing it would affect every collection that holds vertices.

Verifying these changes

• Trivial rework / code cleanup without any test coverage. (No Need)
• Already covered by existing tests, such as (please modify tests here).
• Need tests and can be verified as follows:
  • New MapLimitIteratorTest (added to CoreSuiteTest) feeds two fresh BaseVertex objects per id through MapLimitIterator. Before the change it emitted 20 elements for 10 ids; now it emits 10.
  • FilterIteratorColumnEqualityTest, FilterIteratorContractTest, ProjectionStageTest, UnionFilterIteratorTest and FilterIteratorCleanupTest still pass.

Does this PR potentially affect the following parts?

• Dependencies
• Modify configurations
• The public API
• Other affects (typed here)
• Nope

Documentation Status

• Doc - TODO: required documentation is pending; complete it before merging.
• Doc - Done: documentation is included here or linked below.
• Doc - No Need: no user-visible documentation is affected.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 58.42%. Comparing base (8e327b8) to head (c76f6c6).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
.../hugegraph/store/business/BusinessHandlerImpl.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #3451   +/-   ##
=========================================
  Coverage     58.42%   58.42%           
- Complexity     6903     6905    +2     
=========================================
  Files           779      779           
  Lines         69391    69391           
  Branches       9567     9567           
=========================================
  Hits          40539    40539           
- Misses        25179    25181    +2     
+ Partials       3673     3671    -2     

Flag	Coverage Δ		*Carryforward flag
commons	96.37% <ø> (ø)		Carriedforward from 8e327b8
hstore	36.08% <ø> (ø)		Carriedforward from 8e327b8
pd	56.74% <ø> (ø)		Carriedforward from 8e327b8
server_hbase	42.58% <ø> (ø)		Carriedforward from 8e327b8
server_memory	56.52% <ø> (ø)		Carriedforward from 8e327b8
server_rocksdb	43.03% <ø> (ø)		Carriedforward from 8e327b8
store	35.96% <0.00%> (ø)

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