/efcore-patterns

name: efcore-patterns
description: Entity Framework Core best practices including NoTracking by default, query splitting for navigation collections, migration management, dedicated migration services, and common pitfalls to avoid.
user-invocable: false

Entity Framework Core Patterns

When to Use This Skill

Use this skill when:

• Setting up EF Core in a new project
• Optimizing query performance
• Managing database migrations
• Integrating EF Core with .NET Aspire
• Debugging change tracking issues
• Loading multiple navigation collections efficiently (query splitting)

Core Principles

1. **NoTracking by Default** - Most queries are read-only; opt-in to tracking 2. **Never Edit Migrations Manually** - Always use CLI commands 3. **Dedicated Migration Service** - Separate migration execution from application startup 4. **ExecutionStrategy for Retries** - Handle transient database failures 5. **Explicit Updates** - When NoTracking, explicitly mark entities for update

---

Pattern 1: NoTracking by Default

Configure your DbContext to disable change tracking by default. This improves performance for read-heavy workloads.

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
        // Disable change tracking by default for better performance on read-only queries
        // Use .AsTracking() explicitly for queries that need to track changes
        ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
    }

    public DbSet<Order> Orders => Set<Order>();
    public DbSet<Customer> Customers => Set<Customer>();
}

When NoTracking is Active

**Read-only queries work normally:**

// ✅ Fast read - no tracking overhead
var orders = await dbContext.Orders
    .Where(o => o.Status == OrderStatus.Pending)
    .ToListAsync();

**Writes require explicit handling:**

// ❌ WRONG - Entity not tracked, SaveChanges does nothing
var order = await dbContext.Orders.FirstOrDefaultAsync(o => o.Id == orderId);
order.Status = OrderStatus.Shipped;
await dbContext.SaveChangesAsync(); // Nothing happens!

// ✅ CORRECT - Explicitly mark entity for update
var order = await dbContext.Orders.FirstOrDefaultAsync(o => o.Id == orderId);
order.Status = OrderStatus.Shipped;
dbContext.Orders.Update(order); // Marks entire entity as modified
await dbContext.SaveChangesAsync();

// ✅ ALSO CORRECT - Use AsTracking() for the query
var order = await dbContext.Orders
    .AsTracking()
    .FirstOrDefaultAsync(o => o.Id == orderId);
order.Status = OrderStatus.Shipped;
await dbContext.SaveChangesAsync(); // Works!

When to Use Tracking

| Scenario | Use Tracking? | Why | |----------|---------------|-----| | Display data in UI | No | Read-only, no updates | | API GET endpoints | No | Returning data, no mutations | | Update single entity | Yes or explicit Update() | Need to save changes | | Complex update with navigation | Yes | Tracking handles relationships | | Batch operations | No + ExecuteUpdate | More efficient |

Explicit Add/Update Pattern

public class OrderService
{
    private readonly ApplicationDbContext _db;

    // CREATE - Always use Add (works regardless of tracking)
    public async Task<Order> CreateOrderAsync(Order order)
    {
        _db.Orders.Add(order);
        await _db.SaveChangesAsync();
        return order;
    }

    // UPDATE - Explicitly mark as modified
    public async Task UpdateOrderStatusAsync(Guid orderId, OrderStatus newStatus)
    {
        var order = await _db.Orders.FirstOrDefaultAsync(o => o.Id == orderId)
            ?? throw new NotFoundException($"Order {orderId} not found");

        order.Status = newStatus;
        order.UpdatedAt = DateTimeOffset.UtcNow;

        // Explicitly mark as modified since DbContext uses NoTracking by default
        _db.Orders.Update(order);
        await _db.SaveChangesAsync();
    }

    // DELETE - Attach and remove
    public async Task DeleteOrderAsync(Guid orderId)
    {
        var order = new Order { Id = orderId };
        _db.Orders.Remove(order);
        await _db.SaveChangesAsync();
    }
}

---

Pattern 2: Never Edit Migrations Manually

**CRITICAL:** Always use EF Core CLI commands to manage migrations. Never:

• Manually edit migration files (except for custom SQL in `Up()`/`Down()`)
• Delete migration files directly
• Rename migration files
• Copy migrations between projects

Creating Migrations

# Create a new migration
dotnet ef migrations add AddCustomerTable \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

# With a specific DbContext (if you have multiple)
dotnet ef migrations add AddCustomerTable \
    --context ApplicationDbContext \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

Removing Migrations

# Remove the last migration (if not yet applied)
dotnet ef migrations remove \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

# NEVER do this:
# rm Migrations/20240101_AddCustomerTable.cs  # ❌ BAD!

Applying Migrations

# Apply all pending migrations
dotnet ef database update \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

# Apply to a specific migration
dotnet ef database update AddCustomerTable \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

# Rollback to a previous migration
dotnet ef database update PreviousMigrationName \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

Generating SQL Scripts

# Generate SQL script for all migrations
dotnet ef migrations script \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api \
    --output migrations.sql

# Generate idempotent script (safe to run multiple times)
dotnet ef migrations script \
    --idempotent \
    --proje