Model Building

Metadata Interface Hierarchy

IReadOnly* → IMutable* → IConvention* → IRuntime*

Applies to: Model, EntityType, Property, Key, ForeignKey, Navigation, Index, etc. Builders follow: *Builder → IConvention*Builder.

Model Lifecycle

1. Mutable Model — built by ModelBuilder during OnModelCreating, made read-only by FinalizeModel()
2. Design-Time Model — finalized read-only Model that also contains design-time-only annotations used in migrations
3. Runtime Model — an optimized read-only model created by RuntimeModelConvention.ProcessModelFinalized(), does not contain design-time-only annotations

ModelRuntimeInitializer.Initialize() (called by DbContextServices.CreateModel()):

Initialize(model, designTime, validationLogger)
├─ FinalizeModel() if mutable
├─ Set ModelDependencies, InitializeModel
└─ RuntimeModelConvention creates RuntimeModel, copies/filters annotations

Complex Type Property Recursion

When processing properties in conventions or validation, remember that complex types can contain their own declared properties. Use GetFlattenedProperties() to iterate all properties (including on nested non-collection complex types) or manually recurse through GetDeclaredComplexProperties() → complexProperty.ComplexType.

Adding a New Annotation

1. Add constant to CoreAnnotationNames and its AllNames
2. Filter in RuntimeModelConvention.ProcessModelAnnotations if it's a design-time-only annotation (only used in migration operations)
   1. If it was filtered out, add logic to the getters that throws an exception if accessed on the runtime model
3. Filter in CSharpRuntimeAnnotationCodeGenerator.Generate if it can be computed lazily at runtime (e.g. based on other annotations)
4. Propagate in RelationalAnnotationProvider if used in up-migrations or the relational model and IMigrationsAnnotationProvider if used in down-migrations

Relational Model

RelationalModel (src/EFCore.Relational/Metadata/Internal/RelationalModel.cs) is a database-centric view of the EF model, mapping entity types to physical database objects: Tables, Views, Functions, Queries, and DefaultTables. DefaultTables are pseudo-table objects only used for FromSql queries.

Created lazily by RelationalModelRuntimeInitializer, accessed via model.GetRelationalModel(). Used by migrations (MigrationsModelDiffer), update and query pipelines.

RelationalAnnotationProvider populates annotations on relational model elements. Provider subclasses (e.g., SqlServerAnnotationProvider) add provider-specific annotations. IMigrationsAnnotationProvider controls annotations used in down-migration operations.

Model Validation

ModelValidator (src/EFCore/Infrastructure/ModelValidator.cs) and RelationalModelValidator (src/EFCore.Relational/Infrastructure/RelationalModelValidator.cs) run after model finalization, during ModelRuntimeInitializer.Initialize() between the pre- and post-validation InitializeModel calls.

Migration Snapshot Compatibility

Model-building changes can trigger spurious migrations for users who upgrade. Two causes:

1. New metadata written to the snapshot — old snapshots won't have it; MigrationsModelDiffer sees a diff. Fix: ensure absence of the annotation in an old snapshot is treated as the old default.
2. Annotation renamed or reinterpreted — old snapshots produce a different model. Fix: keep backward-compatible reading logic.

Inspect CSharpSnapshotGenerator (what gets written) and MigrationsModelDiffer (how absence is handled). Add a snapshot round-trip test in test/EFCore.Design.Tests/Migrations/ModelSnapshotSqlServerTest.cs.

Testing

Validation

• Model builds without InvalidOperationException during finalization
• All new API is covered by tests
• Compiled model baselines update cleanly with EF_TEST_REWRITE_BASELINES=1
• ToString() on metadata objects shows concise contents without throwing exceptions
• No spurious migration is generated against a project with an existing snapshot