Add datetime as a datatype for the Neptune LangChain integration

[kwokmeli]

Checked

• I searched existing ideas and did not find a similar one
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• I've clearly described the feature request and motivation for it

Feature request

Datatypes for property values are currently inferred:

langchain/libs/community/langchain_community/graphs/neptune_graph.py

Line 119 in ba74341

types = {

Datetime is currently not a supported datatype to be inferred. As a result, Neptune graphs that use datetime datatypes for properties have their datatypes inferred as strings. LLM-generated openCypher queries to do date/time manipulation (e.g. queries that need to find/filter on date/time ranges) then use string comparison instead of the proper date/time functions, because the schema being passed to the LLM says that these properties are strings when they are actually stored as datetimes.

Motivation

Datetime is a common datatype for properties, as it is often used for versioning, capturing when certain events/entities were established, and for time-to-live. It is common to write queries that filter results according to a date/time range, and needed to implement time-to-live.

Proposal (If applicable)

Add datetime as a supported datatype to be inferred.