Document Cosmos discriminator naming breaking change (EF Core 11)

[Copilot]

Documents the EF Core 11 breaking change from efcore#38458: the default Azure Cosmos DB discriminator property is now named Discriminator in the EF model again, while the property written to the JSON document remains $type by default. The model name and JSON name are now decoupled, so stored documents are unaffected.

Changes

• ef-core-11.0/breaking-changes.md — New low-impact entry (summary-table row + section):
  • Old: $type used as both the model property name and the JSON name; an invalid C# identifier that produced uncompilable code for compiled models / precompiled queries (Native AOT).
  • New: model name reverts to Discriminator; JSON name stays $type. On-disk format unchanged.
  • Mitigations: none needed for stored data; update code that references the model name $type; set the JSON name model-wide via HasEmbeddedDiscriminatorName; per-entity via ToJsonProperty; or restore the old model name with HasDiscriminator<string>("$type").
  • Examples: show how to align the JSON discriminator name with the model property name by configuring it as Discriminator.
• providers/cosmos/modeling.md — Note clarifying model name vs JSON name and documenting the previously undocumented model-wide HasEmbeddedDiscriminatorName API, including an example that aligns the JSON discriminator name with the model property name.

Setting the JSON name to match the model name

modelBuilder.HasEmbeddedDiscriminatorName("Discriminator");

[Copilot]

Pull request overview

Documents an EF Core 11 Cosmos DB breaking change where the discriminator’s model property name is Discriminator again while the JSON property name remains $type by default, clarifying that stored documents are unaffected.

Changes:

• Adds a new low-impact breaking change entry describing the discriminator model-name vs JSON-name decoupling and mitigations.
• Updates Cosmos modeling docs with an EF Core 11 note and documents the model-wide HasEmbeddedDiscriminatorName API.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
entity-framework/core/what-is-new/ef-core-11.0/breaking-changes.md	Adds a new EF Core 11 breaking-change section and summary-table row explaining the Cosmos discriminator naming change and mitigations.
entity-framework/core/providers/cosmos/modeling.md	Adds a note clarifying model vs JSON discriminator naming and points readers to the EF Core 11 breaking change entry.