Audit Trail Pattern (Tam Implementasyon)

1. Base Entity & Interface

public interface IAuditable
{
    DateTime CreatedAt { get; set; }
    string CreatedBy { get; set; }
    DateTime? UpdatedAt { get; set; }
    string? UpdatedBy { get; set; }
}

public abstract class AuditableEntity : IAuditable
{
    public DateTime CreatedAt { get; set; }
    public string CreatedBy { get; set; } = null!;
    public DateTime? UpdatedAt { get; set; }
    public string? UpdatedBy { get; set; }
}

// Entity'ler bundan türer
public class Product : AuditableEntity
{
    public int Id { get; set; }
    public string Name { get; set; } = null!;
    public decimal Price { get; set; }
}

2. Current User Servisi

public interface ICurrentUserService
{
    string? UserId { get; }
    string? UserName { get; }
}

// ASP.NET Core implementasyonu
public class CurrentUserService : ICurrentUserService
{
    private readonly IHttpContextAccessor _accessor;
    public CurrentUserService(IHttpContextAccessor accessor) => _accessor = accessor;

    public string? UserId => _accessor.HttpContext?.User?.FindFirst(ClaimTypes.NameIdentifier)?.Value;
    public string? UserName => _accessor.HttpContext?.User?.Identity?.Name;
}

3. SaveChanges Override (Basit Audit)

public class AppDbContext : DbContext
{
    private readonly ICurrentUserService _currentUser;

    public AppDbContext(DbContextOptions<AppDbContext> options, ICurrentUserService currentUser)
        : base(options) => _currentUser = currentUser;

    public override async Task<int> SaveChangesAsync(CancellationToken ct = default)
    {
        var now = DateTime.UtcNow;
        var user = _currentUser.UserName ?? "System";

        foreach (var entry in ChangeTracker.Entries<IAuditable>())
        {
            switch (entry.State)
            {
                case EntityState.Added:
                    entry.Entity.CreatedAt = now;
                    entry.Entity.CreatedBy = user;
                    break;

                case EntityState.Modified:
                    entry.Entity.UpdatedAt = now;
                    entry.Entity.UpdatedBy = user;
                    // CreatedAt/By değiştirilemesin
                    entry.Property(e => e.CreatedAt).IsModified = false;
                    entry.Property(e => e.CreatedBy).IsModified = false;
                    break;
            }
        }

        return await base.SaveChangesAsync(ct);
    }
}

4. Detaylı Audit Log (Değişiklik Geçmişi)

// Audit log entity — her değişiklik bir kayıt
public class AuditLog
{
    public long Id { get; set; }
    public string EntityName { get; set; } = null!;
    public string EntityId { get; set; } = null!;
    public string Action { get; set; } = null!;       // Insert, Update, Delete
    public string? Changes { get; set; }               // JSON: eski→yeni değerler
    public string UserId { get; set; } = null!;
    public DateTime Timestamp { get; set; }
}

// SaveChanges'ta audit log oluşturma
private List<AuditLog> CreateAuditLogs()
{
    var logs = new List<AuditLog>();
    var user = _currentUser.UserId ?? "System";

    foreach (var entry in ChangeTracker.Entries()
        .Where(e => e.State is EntityState.Added or EntityState.Modified or EntityState.Deleted))
    {
        var log = new AuditLog
        {
            EntityName = entry.Entity.GetType().Name,
            EntityId = entry.Properties.FirstOrDefault(p => p.Metadata.IsPrimaryKey())
                            ?.CurrentValue?.ToString() ?? "",
            Action = entry.State.ToString(),
            UserId = user,
            Timestamp = DateTime.UtcNow
        };

        if (entry.State == EntityState.Modified)
        {
            var changes = new Dictionary<string, object?>();
            foreach (var prop in entry.Properties.Where(p => p.IsModified))
            {
                changes[prop.Metadata.Name] = new
                {
                    Old = prop.OriginalValue,
                    New = prop.CurrentValue
                };
            }
            log.Changes = JsonSerializer.Serialize(changes);
        }

        logs.Add(log);
    }

    return logs;
}

5. EF Configuration

public class AuditLogConfiguration : IEntityTypeConfiguration<AuditLog>
{
    public void Configure(EntityTypeBuilder<AuditLog> builder)
    {
        builder.ToTable("AuditLogs");
        builder.HasKey(a => a.Id);
        builder.Property(a => a.EntityName).HasMaxLength(100).IsRequired();
        builder.Property(a => a.EntityId).HasMaxLength(50).IsRequired();
        builder.Property(a => a.Action).HasMaxLength(10).IsRequired();
        builder.Property(a => a.Changes).HasColumnType("nvarchar(max)");
        builder.Property(a => a.UserId).HasMaxLength(100).IsRequired();

        builder.HasIndex(a => new { a.EntityName, a.EntityId });
        builder.HasIndex(a => a.Timestamp);
        builder.HasIndex(a => a.UserId);
    }
}

CREATE TABLE [AuditLogs] (
    [Id]         BIGINT IDENTITY(1,1) NOT NULL,
    [EntityName] NVARCHAR(100) NOT NULL,
    [EntityId]   NVARCHAR(50)  NOT NULL,
    [Action]     NVARCHAR(10)  NOT NULL,
    [Changes]    NVARCHAR(MAX) NULL,
    [UserId]     NVARCHAR(100) NOT NULL,
    [Timestamp]  DATETIME2     NOT NULL,
    CONSTRAINT [PK_AuditLogs] PRIMARY KEY ([Id])
);

CREATE INDEX [IX_AuditLogs_Entity] ON [AuditLogs] ([EntityName], [EntityId]);
CREATE INDEX [IX_AuditLogs_Timestamp] ON [AuditLogs] ([Timestamp]);
CREATE INDEX [IX_AuditLogs_UserId] ON [AuditLogs] ([UserId]);

CREATE TABLE audit_logs (
    id          BIGINT GENERATED ALWAYS AS IDENTITY,
    entity_name VARCHAR(100) NOT NULL,
    entity_id   VARCHAR(50)  NOT NULL,
    action      VARCHAR(10)  NOT NULL,
    changes     JSONB        NULL,          -- JSONB: indexlenebilir, sorgulanabilir!
    user_id     VARCHAR(100) NOT NULL,
    timestamp   TIMESTAMPTZ  NOT NULL,
    CONSTRAINT pk_audit_logs PRIMARY KEY (id)
);

CREATE INDEX ix_audit_logs_entity ON audit_logs (entity_name, entity_id);
CREATE INDEX ix_audit_logs_timestamp ON audit_logs (timestamp);
CREATE INDEX ix_audit_logs_user_id ON audit_logs (user_id);

-- Bonus: JSONB changes üzerine GIN index (hangi alanlar değişti sorguları için)
CREATE INDEX ix_audit_logs_changes ON audit_logs USING gin (changes);

Örnek AuditLog verisi: