Validate that ownership relationships keep their default DeleteBehavior and requiredness

[Copilot]

Bulk mutations like foreach (var fk in model.GetForeignKeys()) fk.DeleteBehavior = DeleteBehavior.Restrict; silently overwrite the Cascade behavior that ownership FKs require. The runtime keeps treating the relationship as a cascading required ownership while the migrations snapshot reflects the user-set value, producing endless drop/recreate FK migrations (#33625 and many duplicates).

Per @AndriySvyryd, surface this as a model validation error instead of letting the model be silently inconsistent.

Changes

• ModelValidator.ValidateOwnership — throw when the ownership FK has DeleteBehavior != Cascade or IsRequired == false.
• CoreStrings — two new messages:
  • OwnershipNotCascadeDelete(principal, dependent, deleteBehavior, cascadeBehavior)
  • OwnershipNotRequired(principal, dependent)
• ModelValidatorTest — Detects_ownership_with_non_cascade_delete_behavior and Detects_optional_ownership.

Example

modelBuilder.Entity<Blog>().OwnsOne(b => b.Metadata);

// Now throws on model finalization instead of silently corrupting migrations:
foreach (var fk in modelBuilder.Model.GetEntityTypes().SelectMany(t => t.GetForeignKeys()))
{
    fk.DeleteBehavior = DeleteBehavior.Restrict;
}

The ownership relationship from 'Blog' to 'Blog.Metadata#Metadata' is configured with 'Restrict' delete behavior. Ownership relationships must use 'Cascade' delete behavior. Either remove the explicit delete behavior configuration or don't configure this relationship as an ownership.

Breaking change note

Models that previously built successfully while overriding DeleteBehavior/IsRequired on ownership FKs will now fail validation. The runtime behavior was already ignoring these overrides, so the only fix on the user side is to skip ownership FKs when applying the override.

[Copilot]

Pull request overview

This pull request strengthens EF Core’s model validation to prevent ownership relationships from becoming internally inconsistent when users bulk-mutate foreign keys (e.g., setting DeleteBehavior globally). It ensures that ownership FKs cannot be configured away from the semantics EF Core requires, avoiding endless “drop/recreate FK” migrations caused by mismatched snapshot vs. runtime expectations.

Changes:

• Add model validation errors for ownership foreign keys configured with non-Cascade DeleteBehavior.
• Add model validation errors for ownership foreign keys configured as optional (IsRequired == false).
• Add corresponding localized error strings and unit tests covering both invalid configurations.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
test/EFCore.Tests/Infrastructure/ModelValidatorTest.cs	Adds regression tests for ownership FK DeleteBehavior != Cascade and IsRequired == false.
src/EFCore/Properties/CoreStrings.resx	Adds two new user-facing validation messages for invalid ownership FK configuration.
src/EFCore/Properties/CoreStrings.Designer.cs	Adds strongly-typed accessors for the new CoreStrings messages.
src/EFCore/Infrastructure/ModelValidator.cs	Implements the new ownership validation checks in ValidateOwnership.

Files not reviewed (1)

• src/EFCore/Properties/CoreStrings.Designer.cs: Generated file

[Copilot]

Pull request overview

Copilot reviewed 7 out of 8 changed files in this pull request and generated no new comments.

Files not reviewed (1)

• src/EFCore/Properties/CoreStrings.Designer.cs: Generated file