Add support for SQL window functions in ExpressiveSharp.EntityFrameworkCore

[koenbeuk]

Summary

Adds SQL window function support (ROW_NUMBER, RANK, DENSE_RANK, NTILE) and indexed Select to ExpressiveSharp via a new ExpressiveSharp.EntityFrameworkCore.Relational package.

Setup

dotnet add package ExpressiveSharp.EntityFrameworkCore.Relational

var options = new DbContextOptionsBuilder<MyDbContext>()
    .UseSqlServer(connectionString)
    .UseExpressives(o => o.UseRelationalExtensions())
    .Options;

What this enables

Ranking rows within a result set

// "Show me each order's position when sorted by price"
db.Orders.Select(o => new
{
    o.Id,
    o.Price,
    Position = WindowFunction.RowNumber(Window.OrderBy(o.Price))
});
// SQL: SELECT Id, Price, ROW_NUMBER() OVER(ORDER BY Price) FROM Orders

Ranking with ties

// "Rank customers' orders by price — ties get the same rank"
db.Orders.Select(o => new
{
    o.Id,
    o.CustomerId,
    PriceRank = WindowFunction.Rank(
        Window.PartitionBy(o.CustomerId).OrderByDescending(o.Price))
});
// SQL: SELECT Id, CustomerId,
//   RANK() OVER(PARTITION BY CustomerId ORDER BY Price DESC)
// FROM Orders

Dense ranking (no gaps after ties)

// "Same as RANK but without gaps — if two items tie for 2nd, the next is 3rd (not 4th)"
db.Orders.Select(o => new
{
    o.Id,
    Dense = WindowFunction.DenseRank(Window.OrderBy(o.Price))
});
// SQL: SELECT Id, DENSE_RANK() OVER(ORDER BY Price) FROM Orders

Distributing rows into buckets

// "Split orders into 4 roughly equal price quartiles"
db.Orders.Select(o => new
{
    o.Id,
    Quartile = WindowFunction.Ntile(4, Window.OrderBy(o.Price))
});
// SQL: SELECT Id, NTILE(4) OVER(ORDER BY Price) FROM Orders

Indexed Select (zero-based row index)

// "Give me each order with its 0-based position in the result"
db.ExpressiveSet<Order>()
    .OrderBy(o => o.Price)
    .Select((o, index) => new { o.Id, o.Price, Position = index });
// SQL: SELECT Id, Price,
//   CAST(ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) - 1 AS INTEGER) AS Position
// FROM Orders ORDER BY Price

Combining with ExpressiveSharp features

// Window functions + null-conditional operators + [Expressive] properties
db.ExpressiveSet<Order>()
    .Where(o => o.Customer?.Name != null)
    .Select(o => new
    {
        o.Id,
        CustomerName = o.Customer?.Name,
        Rank = WindowFunction.DenseRank(
            Window.PartitionBy(o.CustomerId).OrderBy(o.Total))
    });

Architecture

• New package: ExpressiveSharp.EntityFrameworkCore.Relational — depends on Microsoft.EntityFrameworkCore.Relational, keeping the base EF Core package provider-agnostic
• Plugin system: ExpressiveOptionsBuilder with UseRelationalExtensions() — explicit opt-in, no fragile assembly scanning
• Provider-agnostic: ROW_NUMBER uses EF Core's built-in RowNumberExpression; RANK/DENSE_RANK/NTILE use a self-rendering WindowFunctionSqlExpression that works with any provider's QuerySqlGenerator (no generator replacement)
• Indexed Select: Implemented as an IExpressionTreeTransformer that rewrites Queryable.Select((item, index) => ...) to inject ROW_NUMBER() - 1

Test plan

• SQL shape tests — exact SQL string assertions for all window functions (SQLite)
• Integration tests — seed data, execute queries, verify actual result values (ties, partitioning, bucket distribution)
• Indexed Select — SQL shape + end-to-end with zero-based index verification
• All 1175 existing tests pass — zero regressions
• Both net8.0 and net10.0 target frameworks

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a new relational extension package to the ExpressiveSharp EF Core integration, enabling SQL window functions and indexed Select support via an opt-in plugin model (UseExpressives(o => o.UseRelationalExtensions())).

Changes:

• Introduces ExpressiveSharp.EntityFrameworkCore.Relational with window function stubs (WindowFunction, Window) and EF Core translation/rendering infrastructure.
• Adds a plugin system to ExpressiveSharp.EntityFrameworkCore (IExpressivePlugin + ExpressiveOptionsBuilder) so relational features can be enabled selectively.
• Extends the interceptor generator and stubs to support Select((elem, index) => ...), plus a transformer that rewrites indexed selects to ROW_NUMBER().

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
tests/ExpressiveSharp.EntityFrameworkCore.Relational.Tests/WindowFunctionTests.cs	New SQL-shape + integration tests for window functions and indexed Select.
tests/ExpressiveSharp.EntityFrameworkCore.Relational.Tests/Models/WindowTestDbContext.cs	Minimal EF Core model/context for relational window-function tests.
tests/ExpressiveSharp.EntityFrameworkCore.Relational.Tests/Models/TestModels.cs	Test entities (Customer, Order).
tests/ExpressiveSharp.EntityFrameworkCore.Relational.Tests/ExpressiveSharp.EntityFrameworkCore.Relational.Tests.csproj	New MSTest project wiring for relational tests.
src/ExpressiveSharp/Extensions/RewritableQueryableLinqExtensions.cs	Adds delegate-stub overload for indexed Select on IRewritableQueryable<T>.
src/ExpressiveSharp.Generator/PolyfillInterceptorGenerator.cs	Adds interceptor emission for indexed Select(Func<T,int,TResult>).
src/ExpressiveSharp.EntityFrameworkCore/Infrastructure/Internal/ExpressiveOptionsExtension.cs	Adds plugin application and plugin-based EF internal service provider hashing.
src/ExpressiveSharp.EntityFrameworkCore/IExpressivePlugin.cs	New plugin interface for registering services + transformers.
src/ExpressiveSharp.EntityFrameworkCore/Extensions/DbContextOptionsExtensions.cs	Adds UseExpressives(Action<ExpressiveOptionsBuilder>) overload for plugin configuration.
src/ExpressiveSharp.EntityFrameworkCore/ExpressiveOptionsBuilder.cs	New builder used by UseExpressives(...) to register plugins.
src/ExpressiveSharp.EntityFrameworkCore.Relational/WindowFunctions/WindowFunction.cs	Public window function stubs (translated to SQL).
src/ExpressiveSharp.EntityFrameworkCore.Relational/WindowFunctions/WindowDefinition.cs	Marker/fluent API for building window specs in expression trees.
src/ExpressiveSharp.EntityFrameworkCore.Relational/WindowFunctions/Window.cs	Static entry point for window spec creation.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Transformers/RewriteIndexedSelectToRowNumber.cs	Rewrites indexed Queryable.Select to ROW_NUMBER() - 1.
src/ExpressiveSharp.EntityFrameworkCore.Relational/RelationalExpressivePlugin.cs	Registers relational translation services + transformers via plugin.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowSpecSqlExpression.cs	Intermediate SQL node carrying PARTITION/ORDER clauses.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowSpecMethodCallTranslator.cs	Translates Window/WindowDefinition calls into WindowSpecSqlExpression.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowFunctionTranslatorPlugin.cs	Registers method-call translators into EF Core pipeline.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowFunctionSqlNullabilityProcessor.cs	Marks window function SQL nodes as non-nullable during nullability processing.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowFunctionSqlExpression.cs	Custom SQL expression type for RANK/DENSE_RANK/NTILE window functions.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowFunctionParameterBasedSqlProcessorFactory.cs	Factory wiring for custom parameter-based SQL processor.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowFunctionParameterBasedSqlProcessor.cs	Hooks custom nullability processor into EF’s relational SQL processing.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowFunctionMethodCallTranslator.cs	Translates WindowFunction.* calls into EF SQL expressions.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/WindowFunctionEvaluatableExpressionFilter.cs	Prevents client-evaluation of window-function marker methods.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/ExpressiveRelationalQuerySqlGeneratorFactory.cs	Attempts to provide a SQL generator that can render custom window-function SQL nodes.
src/ExpressiveSharp.EntityFrameworkCore.Relational/Infrastructure/Internal/ExpressiveRelationalQuerySqlGenerator.cs	Adds SQL rendering for WindowFunctionSqlExpression.
src/ExpressiveSharp.EntityFrameworkCore.Relational/ExpressiveSharp.EntityFrameworkCore.Relational.csproj	New relational package project with EF Core Relational references per TFM.
src/ExpressiveSharp.EntityFrameworkCore.Relational/ExpressiveOptionsBuilderExtensions.cs	Adds UseRelationalExtensions() plugin registration extension.
README.md	Documents relational package installation and window function usage.
ExpressiveSharp.slnx	Adds the new relational project and its test project to the solution.
Directory.Packages.props	Adds central version for Microsoft.EntityFrameworkCore.Relational.
CLAUDE.md	Updates repo/module map and test listing to include relational project/tests.

---

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[Copilot]

Ntile_DistributesIntoBuckets computes bucket counts but doesn't assert the expected distribution (the comment says 3,3,2,2 for 10 rows into 4 buckets). As written, the test would still pass even if NTILE were translated incorrectly as long as values stay within 1..4 and all buckets appear. Add assertions for the expected per-bucket counts (and/or expected ordering) to make this test effective.

[Copilot]

The XML docs on RelationalExpressivePlugin have two consecutive <summary> blocks, and the first one mentions auto-discovery via ExpressivePluginAttribute even though no such attribute is present/used in this PR. This will generate malformed/unhelpful docs and is misleading for consumers. Collapse to a single <summary> and describe the actual activation mechanism (UseExpressives(o => o.UseRelationalExtensions())).

Suggested change

	/// Plugin that registers window function services into the EF Core service provider.
	/// Auto-discovered via <see cref="ExpressivePluginAttribute"/> when the assembly is loaded.
	/// </summary>
	/// <summary>
	/// Plugin that registers window function services into the EF Core service provider.
	/// Activated via <c>.UseExpressives(o => o.UseRelationalExtensions())</c>.
	/// </summary>
	/// Plugin that registers window function services into the EF Core service provider,
	/// activated via <c>.UseExpressives(o => o.UseRelationalExtensions())</c>.
	/// </summary>

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'ExpressiveSharp Benchmarks'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 8bb95ff	Previous: ecfbc5e	Ratio
ExpressiveSharp.Benchmarks.ExpressionReplacerBenchmarks.Replace_Method	2741.0256703694663 ns (± 1505.0785066694834)	2228.660212198893 ns (± 1112.9733320962775)	1.23
ExpressiveSharp.Benchmarks.EFCoreQueryOverheadBenchmarks.WithExpressives_Method	28230.931579589844 ns (± 9372.08233244819)	22196.46024576823 ns (± 6676.912910179035)	1.27
ExpressiveSharp.Benchmarks.ExpressionReplacerBenchmarks.Replace_BlockBody	6257.154693603516 ns (± 2725.442629531928)	3140.7159576416016 ns (± 64.07807556687932)	1.99
ExpressiveSharp.Benchmarks.GeneratorBenchmarks.RunGenerator_NoiseChange(ExpressiveCount: 1)	2730364.2083333335 ns (± 692274.6929494727)	2136743.9348958335 ns (± 82866.55228766914)	1.28
ExpressiveSharp.Benchmarks.GeneratorBenchmarks.RunGenerator_Incremental_ExpressiveChange(ExpressiveCount: 100)	5457064.161458333 ns (± 710937.7021331617)	4202663.296875 ns (± 310669.68796058506)	1.30
ExpressiveSharp.Benchmarks.GeneratorBenchmarks.RunGenerator_Incremental_ExpressiveChange(ExpressiveCount: 1000)	13321867.385416666 ns (± 488251.425311472)	10671169.744791666 ns (± 358374.5233719214)	1.25

This comment was automatically generated by workflow using github-action-benchmark.