Proxy

Definition

The Proxy pattern provides a substitute or intermediary that controls access to an object. The proxy intercepts calls to add behavior (audit, filtering, validation) transparently.

In Granit, two Proxy variants are used: the FilterProxy for EF Core query filters, and EF Core Interceptors that intercept SaveChangesAsync().

Diagram

sequenceDiagram
    participant App as Application
    participant DB as DbContext
    participant AI as AuditedEntityInterceptor
    participant SDI as SoftDeleteInterceptor
    participant EF as EF Core Engine

    App->>DB: SaveChangesAsync()
    DB->>AI: SavingChangesAsync()
    AI->>AI: Iterate ChangeTracker entries
    AI->>AI: Added: CreatedAt, CreatedBy, TenantId
    AI->>AI: Modified: ModifiedAt, ModifiedBy
    DB->>SDI: SavingChangesAsync()
    SDI->>SDI: Deleted becomes Modified (IsDeleted=true)
    SDI->>SDI: DeletedAt, DeletedBy
    DB->>EF: Execute SQL queries

Implementation in Granit

FilterProxy (property proxy for EF Core)

Component	File	Role
FilterProxy	src/Granit.Persistence/Extensions/ModelBuilderExtensions.cs (lines 133-140)	Exposes boolean properties (SoftDeleteEnabled, ActiveEnabled, MultiTenantEnabled) so EF Core can extract them as query parameters

EF Core cannot translate arbitrary method calls in query filters. The FilterProxy works around this limitation by exposing simple properties that EF Core treats as SQL parameters.

EF Core Interceptors

Interceptor	File	Role
AuditedEntityInterceptor	src/Granit.Persistence/Interceptors/AuditedEntityInterceptor.cs	Injects CreatedAt/By, ModifiedAt/By, TenantId, Id (sequential)
SoftDeleteInterceptor	src/Granit.Persistence/Interceptors/SoftDeleteInterceptor.cs	Converts DELETE to UPDATE with IsDeleted=true, DeletedAt/By

Rationale

EF Core interceptors apply cross-cutting rules (ISO 27001 audit, GDPR soft delete) transparently without polluting application handlers. The FilterProxy solves a technical EF Core limitation while keeping filters dynamic.

Usage example

// The application never sees the interceptors -- they are transparent
Patient patient = new()
{
    FirstName = "Jean",
    LastName = "Dupont"
};

db.Patients.Add(patient);
await db.SaveChangesAsync(ct);

// AuditedEntityInterceptor has automatically populated:
// patient.Id = Sequential Guid (IGuidGenerator)
// patient.CreatedAt = DateTimeOffset.UtcNow (IClock)
// patient.CreatedBy = "user-123" (ICurrentUserService)
// patient.TenantId = Current tenant Guid (ICurrentTenant)

// Deletion is intercepted by SoftDeleteInterceptor:
db.Patients.Remove(patient);
await db.SaveChangesAsync(ct);
// -> UPDATE Patients SET IsDeleted=1, DeletedAt=..., DeletedBy=... WHERE Id=...
// -> No physical DELETE

Further reading

• Proxy — refactoring.guru