--- name: managedcode/entity-framework-core source: https://app.decimal.ai/s/managedcode-entity-framework-core@2/SKILL.md source_sha256: 1cd6f8d4518b --- # Entity Framework Core ## Trigger On - working on `DbContext`, migrations, model configuration, or EF queries - reviewing tracking, loading, performance, or transaction behavior - porting data access from EF6 or custom repositories to EF Core - optimizing slow database queries ## Documentation - [EF Core Overview](https://learn.microsoft.com/en-us/ef/core/) - [Performance](https://learn.microsoft.com/en-us/ef/core/performance/) - [Efficient Querying](https://learn.microsoft.com/en-us/ef/core/performance/efficient-querying) - [Migrations](https://learn.microsoft.com/en-us/ef/core/managing-schemas/migrations/) - [What's New in EF Core 9](https://learn.microsoft.com/en-us/ef/core/what-is-new/ef-core-9.0/whatsnew) ### References - [patterns.md](references/patterns.md) - Query patterns, tracking strategies, loading strategies, projections, compiled queries, pagination, and temporal tables - [anti-patterns.md](references/anti-patterns.md) - Common EF Core mistakes including N+1 queries, large contexts, generic repositories, and missing indexes ## Workflow 1. **Prefer EF Core for new development** unless a documented gap requires Dapper or raw SQL 2. **Keep `DbContext` lifetime scoped** — align with unit of work 3. **Review query translation** — check generated SQL, avoid N+1 4. **Treat migrations as first-class** — reviewable, not throwaway 5. **Be deliberate about provider behavior** — cross-provider but not identical 6. **Validate with query inspection** — not just in-memory mental model ## Current Upstream Notes - EF Core `v10.0.11` is a servicing release. It fixes Azure SQL compatibility-level 170 JSON translation so nested `OPENJSON` projections retain `AS JSON`, and keeps EF compatible with .NET 11 `MemoryExtensions.Min`/`Max` overload additions. Re-run provider-backed JSON queries and compile against the repository's selected target framework after upgrading. - The August 2026 EF Core vs EF6 comparison remains the first stop for migration decisions. EF Core is the active cross-platform stack, but EF6-only EDMX/ObjectContext-heavy code should not move without a feature inventory and database-backed equivalence tests. ## DbContext Patterns ### Basic Configuration ```csharp public class AppDbContext : DbContext { public DbSet Products => Set(); public DbSet Orders => Set(); protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly); } } // Entity Configuration (Fluent API) public class ProductConfiguration : IEntityTypeConfiguration { public void Configure(EntityTypeBuilder builder) { builder.HasKey(p => p.Id); builder.Property(p => p.Name).HasMaxLength(200).IsRequired(); builder.HasIndex(p => p.Sku).IsUnique(); builder.HasMany(p => p.OrderItems).WithOne(oi => oi.Product); } } ``` ### Registration with DI ```csharp builder.Services.AddDbContext(options => options.UseSqlServer(connectionString) .EnableSensitiveDataLogging() // Dev only .EnableDetailedErrors()); // Dev only // Or with pooling (better performance) builder.Services.AddDbContextPool(options => options.UseSqlServer(connectionString)); ``` ## Query Patterns ### Use AsNoTracking for Read-Only ```csharp // Bad - tracks entities unnecessarily var products = await db.Products.ToListAsync(); // Good - no tracking overhead var products = await db.Products .AsNoTracking() .ToListAsync(); ``` ### Project to DTOs ```csharp // Bad - loads entire entity graph var orders = await db.Orders .Include(o => o.Items) .Include(o => o.Customer) .ToListAsync(); // Good - loads only needed data var orders = await db.Orders .Select(o => new OrderDto { Id = o.Id, CustomerName = o.Customer.Name, ItemCount = o.Items.Count, Total = o.Items.Sum(i => i.Price) }) .ToListAsync(); ``` ### Avoid N+1 Queries ```csharp // Bad - N+1 problem foreach (var order in orders) { var items = await db.OrderItems .Where(i => i.OrderId == order.Id) .ToListAsync(); } // Good - eager loading var orders = await db.Orders .Include(o => o.Items) .ToListAsync(); // Good - split query for large graphs var orders = await db.Orders .Include(o => o.Items) .AsSplitQuery() .ToListAsync(); ``` ### Compiled Queries (EF Core 9) ```csharp // Pre-compiled for frequently used queries private static readonly Func> GetProductById = EF.CompileAsyncQuery((AppDbContext db, int id) => db.Products.FirstOrDefault(p => p.Id == id)); // Usage var product = await GetProductById(db, productId); ``` ## Migration Patterns ### Creating Migrations ```bash # Add migration dotnet ef migrations add AddProductIndex # Apply to database dotnet ef database update # Generate SQL script dotnet ef migrations script --idempotent -o migrate.sql ``` ### Data Migrations ```csharp public partial class AddProductIndex : Migration { protected override void Up(MigrationBuilder migrationBuilder) { migrationBuilder.CreateIndex( name: "IX_Products_Sku", table: "Products", column: "Sku", unique: true); // Data migration (if needed) migrationBuilder.Sql(@" UPDATE Products SET NormalizedName = UPPER(Name) WHERE NormalizedName IS NULL"); } protected override void Down(MigrationBuilder migrationBuilder) { migrationBuilder.DropIndex( name: "IX_Products_Sku", table: "Products"); } } ``` ## Anti-Patterns to Avoid | Anti-Pattern | Why It's Bad | Better Approach | |--------------|--------------|-----------------| | `ToList()` then filter | Loads all data to memory | Filter in query | | Multiple DbContext per request | Transaction issues | Scoped lifetime | | Lazy loading everywhere | N+1 queries | Explicit Include | | Generic repository wrapper | Removes query power | Use DbContext directly | | Ignoring generated SQL | Hidden performance issues | Log and review | | `SaveChanges()` in loops | Many roundtrips | Batch then save | ## Performance Best Practices 1. **Index frequently queried columns:** ```csharp builder.HasIndex(p => p.CreatedAt); builder.HasIndex(p => new { p.Category, p.Status }); ``` 2. **Use pagination:** ```csharp var page = await db.Products .OrderBy(p => p.Id) .Skip(pageSize * pageNumber) .Take(pageSize) .ToListAsync(); ``` 3. **Batch updates (EF Core 7+):** ```csharp await db.Products .Where(p => p.Category == "Obsolete") .ExecuteDeleteAsync(); await db.Products .Where(p => p.Category == "Sale") .ExecuteUpdateAsync(p => p.SetProperty(x => x.Price, x => x.Price * 0.9m)); ``` 4. **Minimize network roundtrips:** ```csharp // Bad - 3 roundtrips var product = await db.Products.FindAsync(id); var reviews = await db.Reviews.Where(r => r.ProductId == id).ToListAsync(); var related = await db.Products.Where(p => p.Category == product.Category).ToListAsync(); // Good - 1 roundtrip var data = await db.Products .Where(p => p.Id == id) .Select(p => new { Product = p, Reviews = p.Reviews, Related = db.Products.Where(r => r.Category == p.Category).Take(5) }) .FirstOrDefaultAsync(); ``` ## Concurrency Patterns ```csharp public class Product { public int Id { get; set; } public string Name { get; set; } [ConcurrencyCheck] public int Version { get; set; } // Or use RowVersion [Timestamp] public byte[] RowVersion { get; set; } } // Handle concurrency conflicts try { await db.SaveChangesAsync(); } catch (DbUpdateConcurrencyException ex) { var entry = ex.Entries.Single(); var databaseValues = await entry.GetDatabaseValuesAsync(); // Resolve conflict... } ``` ## Deliver - EF Core models and queries that match the domain - safer migrations and lifetime management - performance-aware data access decisions - proper indexing and query optimization ## Validate - query behavior is intentional (check SQL logs) - migrations are reviewable and correct - no N+1 queries in common paths - indexes exist for filtered/sorted columns - DbContext lifetime is scoped properly - concurrency is handled for critical entities