Backport 6.1 | API enhancements for vector datatype

[apoorvdeshmukh]

This is a direct port of #3468 from main to release/6.1

[Copilot]

Pull Request Overview

This PR ports issue #3468 from the main branch to the 6.1 release, introducing a CreateNull factory for SqlVector<T>, changing vector handling to a readonly struct, and updating related components and tests.

• Added SqlVector<T>.CreateNull(int length) and replaced constructor calls for null vectors.
• Refactored SqlVector<T> from a sealed class to a readonly struct, moved Size to a private field, and updated interface implementations.
• Updated unit and manual tests, SqlParameter/SqlBuffer handling, SqlDataReader logic, reference assemblies, and documentation to support the new vector API.

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Microsoft.Data.SqlClient/tests/UnitTests/SqlVectorTest.cs	Switched from constructor to CreateNull in null-vector tests and realigned Size assertions.
src/Microsoft.Data.SqlClient/tests/ManualTests/.../NativeVectorFloat32Tests.cs	Updated test data to use vector length only, removed old size parameters, and adjusted parameter size logic.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlTypes/SqlVector.cs	Converted SqlVector<T> to a readonly struct, added CreateNull, and replaced public Size property with an internal field.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlParameter.cs	Ignored Size for vector parameters in setter and Prepare, and updated vector return creation to use CreateNull.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlDataReader.cs	Simplified vector-to-string logic in GetFieldValueFromSqlBufferInternal.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlBuffer.cs	Adjusted GetSqlVector<T> to use CreateNull for null vectors.
src/Microsoft.Data.SqlClient/netfx/ref/Microsoft.Data.SqlClient.cs	Updated reference API for SqlVector<T> to readonly struct and added CreateNull.
src/Microsoft.Data.SqlClient/netcore/ref/Microsoft.Data.SqlClient.cs	Updated reference API for SqlVector<T> to readonly struct and added CreateNull.
doc/snippets/Microsoft.Data.SqlTypes/SqlVector.xml	Added documentation for CreateNull and removed old constructor docs.
doc/snippets/Microsoft.Data.SqlClient/SqlCommand.xml	Clarified that SqlParameter.Size is ignored for vector types.

Comments suppressed due to low confidence (3)

src/Microsoft.Data.SqlClient/tests/ManualTests/SQL/VectorTest/NativeVectorFloat32Tests.cs:20

• [nitpick] The field name sizeInbytes does not follow camelCase conventions (sizeInBytes) and is now unused in tests. Consider renaming to sizeInBytes or removing this dead field to improve readability.

        public static float[] testData = new float[] { 1.1f, 2.2f, 3.3f };

doc/snippets/Microsoft.Data.SqlTypes/SqlVector.xml:12

• [nitpick] The XML element tags for the constructors appear misaligned—there is a closing </ctor1> without a matching <ctor1> and missing <ctor2> tag. Please verify that constructor documentation tags are properly opened and closed.

    </ctor1>

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlDataReader.cs:3366

• The special handling for non-null vectors was removed, so all vector string conversions now return the raw SqlString. This breaks the expected JSON-style output for non-null vectors. Reintroduce the null check and call data.GetSqlVector<float>().GetString() when !data.IsNull.

                    if (typeof(T) == typeof(string) && metaData.metaType.SqlDbType == SqlDbTypeExtensions.Vector)

[paulmedynski]

One typo in a doc comment.

[paulmedynski]

/azp run

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[codecov]

Codecov Report

Attention: Patch coverage is 81.25000% with 3 lines in your changes missing coverage. Please review.

Please upload report for BASE (release/6.1@3396340). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...qlClient/src/Microsoft/Data/SqlClient/SqlBuffer.cs	0.00%	1 Missing ⚠️
...ient/src/Microsoft/Data/SqlClient/SqlDataReader.cs	0.00%	1 Missing ⚠️
...lient/src/Microsoft/Data/SqlClient/SqlParameter.cs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             release/6.1    #3472   +/-   ##
==============================================
  Coverage               ?   68.91%           
==============================================
  Files                  ?      280           
  Lines                  ?    62322           
  Branches               ?        0           
==============================================
  Hits                   ?    42947           
  Misses                 ?    19375           
  Partials               ?        0           

Flag	Coverage Δ
addons	92.58% <ø> (?)
netcore	72.79% <81.25%> (?)
netfx	68.05% <81.25%> (?)

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