feat(neo4j): add apoc_sample parameter for large database schema introspection

[eureka928]

Description

Adds an apoc_sample parameter to both Neo4jGraphStore and Neo4jPropertyGraphStore to control the sampling size used by apoc.meta.data() during schema introspection.

Fixes #18988

On large Neo4j databases, apoc.meta.data() can be very slow because it scans all nodes and relationships. The APOC procedure supports a {sample: N} config parameter to limit sampling, but llama-index was calling it without any config. This change parameterizes the queries with $config and exposes apoc_sample in the constructor.

Usage:

# Without sampling (default, backward-compatible)
store = Neo4jGraphStore(username="neo4j", password="pass", url="bolt://localhost:7687")

# With sampling for large databases
store = Neo4jGraphStore(username="neo4j", password="pass", url="bolt://localhost:7687", apoc_sample=1000)

Changes:

• Parameterized all CALL apoc.meta.data() queries with $config in both base.py and neo4j_property_graph.py
• Added apoc_sample: Optional[int] = None to __init__ of both stores
• Updated refresh_schema() to pass config to all schema queries
• Used is not None check to correctly handle apoc_sample=0 edge case
• Added docstring for the new parameter in Neo4jPropertyGraphStore

New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests

8 unit tests covering both Neo4jGraphStore and Neo4jPropertyGraphStore:

• Default empty config when apoc_sample is not provided
• Config storage when apoc_sample is set
• apoc_sample=0 edge case (not treated as falsy)
• Config correctly passed to all 3 apoc.meta.data queries in refresh_schema()
• EXCLUDED_LABELS still passed alongside config in property graph store

tests/test_apoc_sample.py::TestNeo4jGraphStoreApocSample::test_apoc_sample_default_empty_config PASSED
tests/test_apoc_sample.py::TestNeo4jGraphStoreApocSample::test_apoc_sample_sets_config PASSED
tests/test_apoc_sample.py::TestNeo4jGraphStoreApocSample::test_apoc_sample_zero_is_valid PASSED
tests/test_apoc_sample.py::TestNeo4jGraphStoreApocSample::test_refresh_schema_passes_config PASSED
tests/test_apoc_sample.py::TestNeo4jGraphStoreApocSample::test_refresh_schema_passes_empty_config_by_default PASSED
tests/test_apoc_sample.py::TestNeo4jPropertyGraphStoreApocSample::test_apoc_sample_default_empty_config PASSED
tests/test_apoc_sample.py::TestNeo4jPropertyGraphStoreApocSample::test_apoc_sample_sets_config PASSED
tests/test_apoc_sample.py::TestNeo4jPropertyGraphStoreApocSample::test_refresh_schema_passes_config PASSED

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran uv run make format; uv run make lint to appease the lint gods