[langchain-sqlserver] Use binary collation for custom_id column

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The custom_id column in EmbeddingStore was created without a collation. This adds support for Latin1_General_100_BIN2_UTF8 binary collation on the custom_id column as an opt-in flag for best performance, while preserving backward compatibility for existing deployments by defaulting to the database's collation.

Changes

• BINARY_COLLATION constant — "Latin1_General_100_BIN2_UTF8" defined at module level.
• use_binary_collation_on_custom_id: bool = False — new __init__ parameter; set to True to apply binary collation for best performance. Defaults to False to preserve backward compatibility with existing tables that were created without a forced collation.
• _get_embedding_store() — conditionally passes collation=BINARY_COLLATION to VARCHAR(1000) for custom_id based on the flag.

Usage

# Default: uses the database's collation (backward compatible)
store = SQLServer_VectorStore(
    connection_string=...,
    embedding_function=...,
    embedding_length=1536,
)

# Opt in: binary collation applied for best performance (recommended for new deployments)
store = SQLServer_VectorStore(
    connection_string=...,
    embedding_function=...,
    embedding_length=1536,
    use_binary_collation_on_custom_id=True,
)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[langchain-sqlserver] Use binary collation for custom_id column</issue_title>
<issue_description>To get the best performance possible, binary collation should be used for the custom_id column. Specifically the collation Latin1_General_100_BIN2_UTF8 should be used when creating the custom_id column in the EmbeddingStore function.

To keep backward compatibility and allow users to use the default collation defined for the database, instead of forcing the binary collation, a new option should be introduced in the SQLServer_VectorStore class so that one can opt-out of the forced binary collation, for example:

MySqlServerVectorStore.ForceBinaryComparisonOnCustomId = false
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes [langchain-sqlserver] Use binary collation for custom_id column #74

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Pull request overview

This PR addresses a performance improvement request (#74) by applying Latin1_General_100_BIN2_UTF8 binary collation to the custom_id column in EmbeddingStore, with an opt-out flag for users who prefer the database's default collation.

Changes:

• Adds a BINARY_COLLATION constant at module level in vectorstores.py
• Introduces a new use_binary_collation_on_custom_id: bool = True constructor parameter that conditionally passes the collation to VARCHAR(1000) when building the ORM model
• Adds a new test file test_binary_collation.py covering default behavior, explicit opt-in, opt-out, and the constant value

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
libs/sqlserver/langchain_sqlserver/vectorstores.py	Adds BINARY_COLLATION constant, new __init__ parameter, stores it as _use_binary_collation_on_custom_id, and conditionally applies collation in _get_embedding_store
libs/sqlserver/tests/unit_tests/test_binary_collation.py	New unit tests verifying binary collation is applied by default, when explicitly set to True, and not applied when opted out

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