Allow excluding foreign key from migrations

[roji]

Closes #15854

[Copilot]

Pull request overview

This PR introduces a relational model annotation and fluent API to allow foreign key constraints to exist in the EF model while being excluded from migrations (i.e., migrations won’t create/drop the DB constraint), closing #15854.

Changes:

• Add ExcludeFromMigrations() on relationship builders and persist it via a new relational FK annotation.
• Update migrations diffing to skip add/drop FK operations when a foreign key constraint is excluded.
• Add design-time and functional test coverage (snapshot/codegen + provider SQL baselines) for the new behavior.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/EFCore.Sqlite.FunctionalTests/Migrations/MigrationsSqliteTest.cs	Adds provider SQL assertion for excluded-FK migration (index only).
test/EFCore.SqlServer.FunctionalTests/Migrations/MigrationsSqlServerTest.cs	Adds provider SQL assertion for excluded-FK migration (index only).
test/EFCore.Relational.Tests/Migrations/Internal/MigrationsModelDifferTest.cs	Adds model differ tests validating operations when FK constraints are excluded.
test/EFCore.Relational.Tests/Extensions/RelationalMetadataExtensionsTest.cs	Verifies get/set behavior for the new excluded-from-migrations FK metadata.
test/EFCore.Relational.Tests/Extensions/RelationalBuilderExtensionsTest.cs	Verifies fluent API surface and configuration-source behavior for FK exclusion.
test/EFCore.Relational.Tests/Design/AnnotationCodeGeneratorTest.cs	Ensures snapshot codegen emits ExcludeFromMigrations fluent API for FKs.
test/EFCore.Relational.Specification.Tests/Migrations/MigrationsTestBase.cs	Adds cross-provider scenario ensuring DB FK constraints aren’t created.
test/EFCore.Design.Tests/Migrations/Design/CSharpMigrationsGeneratorTest.cs	Updates “new annotations” guard lists for the new relational annotation name.
test/EFCore.Design.Tests/Migrations/Design/CSharpMigrationsGeneratorTest.ModelSnapshot.cs	Adds snapshot roundtrip test verifying FK exclusion is stored in snapshots.
src/EFCore.Relational/Migrations/Internal/MigrationsModelDiffer.cs	Skips FK add/drop operations when FK constraints are excluded from migrations.
src/EFCore.Relational/Metadata/RelationalAnnotationNames.cs	Introduces IsForeignKeyExcludedFromMigrations annotation name and registers it.
src/EFCore.Relational/Metadata/Internal/ForeignKeyConstraint.cs	Surfaces FK exclusion at the constraint level for migrations diffing.
src/EFCore.Relational/Metadata/IForeignKeyConstraint.cs	Adds IsExcludedFromMigrations to the public constraint metadata interface.
src/EFCore.Relational/Metadata/Conventions/RelationalRuntimeModelConvention.cs	Removes the new annotation from runtime annotations.
src/EFCore.Relational/Extensions/RelationalForeignKeyExtensions.cs	Adds metadata accessors for FK exclusion + configuration source helpers.
src/EFCore.Relational/Extensions/RelationalForeignKeyBuilderExtensions.cs	Adds ExcludeFromMigrations fluent APIs for relationship builders.
src/EFCore.Relational/Design/Internal/RelationalCSharpRuntimeAnnotationCodeGenerator.cs	Removes the new annotation from runtime codegen output.
src/EFCore.Relational/Design/AnnotationCodeGenerator.cs	Generates fluent API calls for FK exclusion in snapshots.

[Copilot]

Adding IsExcludedFromMigrations as a new abstract member on the public IForeignKeyConstraint interface is a binary breaking change for any external implementations. To preserve compatibility, consider providing a default interface implementation (e.g. computing from MappedForeignKeys or returning false) or exposing this via an extension method instead of extending the interface contract.

Suggested change

	bool IsExcludedFromMigrations { get; }
	bool IsExcludedFromMigrations
	=> false;

[roji]

@AndriySvyryd let me know what you want to do here, AFAIK these interfaces aren't meant to be implemented by external users so this is probably not relevant?

[Copilot]

With the new IsForeignKeyExcludedFromMigrations fluent API call generation, if the annotation ever ends up explicitly set to false (e.g. toggled from true back to false), the snapshot will likely emit .ExcludeFromMigrations(false) since RemoveAnnotationsHandledByConventions(IForeignKey, …) doesn’t special-case this annotation. Consider removing this annotation when its value is false (similar to how IsTableExcludedFromMigrations is handled) to avoid noisy/unstable snapshots.

Suggested change

	GenerateSimpleFluentApiCall(
	annotations,
	RelationalAnnotationNames.IsForeignKeyExcludedFromMigrations,
	nameof(RelationalForeignKeyBuilderExtensions.ExcludeFromMigrations),
	methodCallCodeFragments);
	if (annotations.TryGetValue(
	RelationalAnnotationNames.IsForeignKeyExcludedFromMigrations,
	out var excludeFromMigrationsAnnotation)
	&& excludeFromMigrationsAnnotation.Value is bool isExcludedFromMigrations
	&& !isExcludedFromMigrations)
	{
	annotations.Remove(RelationalAnnotationNames.IsForeignKeyExcludedFromMigrations);
	}
	else
	{
	GenerateSimpleFluentApiCall(
	annotations,
	RelationalAnnotationNames.IsForeignKeyExcludedFromMigrations,
	nameof(RelationalForeignKeyBuilderExtensions.ExcludeFromMigrations),
	methodCallCodeFragments);
	}

[roji]

@AndriySvyryd don't we actually prefer to bake in an explicit false when it's explicitly configured by the user?

[roji]

@AndriySvyryd see suggestion to rename this to ExcludeForeignKeyFromMigrations, to make it clear what's being excluded.