Reuse CosmosTypeMapping.Default for primitive JSON reader/writers

[Copilot]

Primitive Cosmos type mappings always allocated a fresh instance via Default.Clone(jsonValueReaderWriter: ...) even though the reader/writer was the well-known singleton, bloating compiled models and preventing reference reuse.

Changes

• JsonValueReaderWriterSource.FindReaderWriter<T>() — new public static generic method using a switch expression to dispatch on typeof(T) to the singleton Json*ReaderWriter.Instance for all primitive types. Enums are handled via JsonSignedEnumReaderWriter<> / JsonUnsignedEnumReaderWriter<> using the same reflection approach as the existing FindReaderWriter(Type) instance method.
• CosmosTypeMapping<T>.Default — now seeded with JsonValueReaderWriterSource.FindReaderWriter<T>() so the default mapping carries its reader/writer.
• CosmosTypeMappingSource.Create<T> — returns Default when the supplied reader/writer is null or reference-equal to Default.JsonValueReaderWriter, instead of only when null.
• Cosmos compiled-model baselines — regenerated; primitives now emit CosmosTypeMapping<T>.Default directly. Converted/enum/collection mappings still emit .Clone(...).

Result

// before
id.TypeMapping = CosmosTypeMapping<int>.Default.Clone(
    jsonValueReaderWriter: JsonInt32ReaderWriter.Instance);

// after
id.TypeMapping = CosmosTypeMapping<int>.Default;

[Copilot]

Pull request overview

This PR reduces Cosmos compiled-model size and allocations by reusing CosmosTypeMapping<T>.Default for primitive JSON reader/writers when the reader/writer is the well-known singleton, instead of emitting/creating Default.Clone(jsonValueReaderWriter: ...) instances.

Changes:

• Seed CosmosTypeMapping<T>.Default with a built-in primitive JsonValueReaderWriter via the new reflection-free CosmosTypeMapping<T>.FindReaderWriter().
• Update CosmosTypeMappingSource.Create<T> to return CosmosTypeMapping<T>.Default when the supplied reader/writer matches Default.JsonValueReaderWriter (or is null).
• Regenerate Cosmos compiled-model baselines to emit CosmosTypeMapping<T>.Default for primitives.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/EFCore.Cosmos/Storage/Internal/CosmosTypeMapping`1.cs	Adds FindReaderWriter() and seeds CosmosTypeMapping<T>.Default with the appropriate primitive JSON reader/writer singleton.
src/EFCore.Cosmos/Storage/Internal/CosmosTypeMappingSource.cs	Reuses CosmosTypeMapping<T>.Default when the provided JSON reader/writer matches the default’s reader/writer.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/Basic_cosmos_model/DataEntityType.cs	Updates baseline to use CosmosTypeMapping<T>.Default directly for primitive mappings where applicable.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/ComplexTypes/PrincipalBaseEntityType.cs	Updates baseline primitive type mappings to reuse CosmosTypeMapping<T>.Default.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/ComplexTypes/PrincipalDerivedEntityType.cs	Updates baseline primitive/element mappings to reuse CosmosTypeMapping<T>.Default where applicable.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/Cosmos_model_with_index_types/IndexedDataEntityType.cs	Updates baseline primitive mappings to reuse CosmosTypeMapping<T>.Default.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/SimpleModel/DependentDerivedEntityType.cs	Updates baseline primitive mappings to reuse CosmosTypeMapping<T>.Default (and removes now-unneeded JSON using).
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/BigModel/DependentBaseEntityType.cs	Updates baseline primitive mappings to reuse CosmosTypeMapping<T>.Default.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/BigModel/DependentDerivedEntityType.cs	Updates baseline primitive mappings to reuse CosmosTypeMapping<T>.Default (and removes now-unneeded JSON using).
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/BigModel/ManyTypesEntityType.cs	Updates baseline primitive/element mappings to reuse CosmosTypeMapping<T>.Default where applicable.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/BigModel/OwnedType0EntityType.cs	Updates baseline primitive/element mappings to reuse CosmosTypeMapping<T>.Default where applicable.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/BigModel/OwnedTypeEntityType.cs	Updates baseline primitive/element mappings to reuse CosmosTypeMapping<T>.Default where applicable.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/BigModel/PrincipalBaseEntityType.cs	Updates baseline primitive/element mappings to reuse CosmosTypeMapping<T>.Default where applicable.
test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/BigModel/PrincipalBasePrincipalDerivedDependentBasebyteEntityType.cs	Updates baseline primitive mappings to reuse CosmosTypeMapping<T>.Default where applicable.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (2)

src/EFCore/Storage/Json/JsonSignedEnumReaderWriter.cs:18

• The generic constraints were removed, so JsonSignedEnumReaderWriter<TEnum> can now be constructed for non-enum TEnum, which will throw later when GetEnumUnderlyingType() is accessed. Add a debug-time guard to make incorrect usage fail fast and with a clearer signal during development.

public sealed class JsonSignedEnumReaderWriter<TEnum> : JsonValueReaderWriter<TEnum>
{
    private static readonly PropertyInfo InstanceProperty = typeof(JsonSignedEnumReaderWriter<TEnum>).GetProperty(nameof(Instance))!;

    /// <summary>
    ///     The singleton instance of this stateless reader/writer.
    /// </summary>
    public static JsonSignedEnumReaderWriter<TEnum> Instance { get; } = new();

src/EFCore/Storage/Json/JsonUnsignedEnumReaderWriter.cs:18

• The generic constraints were removed, so JsonUnsignedEnumReaderWriter<TEnum> can now be constructed for non-enum TEnum, which will throw later when GetEnumUnderlyingType() is accessed. Add a debug-time guard to make incorrect usage fail fast and with a clearer signal during development.

public sealed class JsonUnsignedEnumReaderWriter<TEnum> : JsonValueReaderWriter<TEnum>
{
    private static readonly PropertyInfo InstanceProperty = typeof(JsonUnsignedEnumReaderWriter<TEnum>).GetProperty(nameof(Instance))!;

    /// <summary>
    ///     The singleton instance of this stateless reader/writer.
    /// </summary>
    public static JsonUnsignedEnumReaderWriter<TEnum> Instance { get; } = new();