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

---

DbContext Lifecycle

DbContext is a unit of work and should be short-lived. In ASP.NET Core, register it as scoped (one per request):

builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseNpgsql(builder.Configuration.GetConnectionString("DefaultConnection")));

Lifetime Rules

Scenario	Lifetime	Registration
Web API / MVC request	Scoped (default)	AddDbContext<T>()
Background service	Scoped via factory	AddDbContextFactory<T>()
Blazor Server	Scoped via factory	AddDbContextFactory<T>()
Console app	Transient or manual	new AppDbContext(options)

DbContextFactory for Long-Lived Services

Background services and Blazor Server circuits outlive a single scope. Use IDbContextFactory<T>:

public sealed class OrderProcessor(IDbContextFactory<AppDbContext> contextFactory)
{
    public async Task ProcessBatchAsync(CancellationToken ct)
    {
        await using var db = await contextFactory.CreateDbContextAsync(ct);

        var pending = await db.Orders
            .Where(o => o.Status == OrderStatus.Pending)
            .ToListAsync(ct);

        foreach (var order in pending)
        {
            order.Status = OrderStatus.Processing;
        }

        await db.SaveChangesAsync(ct);
    }
}

builder.Services.AddDbContextFactory<AppDbContext>(options =>
    options.UseNpgsql(builder.Configuration.GetConnectionString("DefaultConnection")));

Pooling

AddDbContextPool<T>() reuses DbContext instances to reduce allocation overhead:

builder.Services.AddDbContextPool<AppDbContext>(options =>
    options.UseNpgsql(connectionString), poolSize: 128);

Pooling constraints: Do not store per-request state on the DbContext subclass. Do not inject scoped services into the constructor.

---

Pattern 1: NoTracking by Default

Configure your DbContext to disable change tracking by default:

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
        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:

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);
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();

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

Per-Query NoTracking

var orders = await db.Orders
    .AsNoTracking()
    .Where(o => o.CustomerId == customerId)
    .ToListAsync(ct);

var ordersWithItems = await db.Orders
    .AsNoTrackingWithIdentityResolution()
    .Include(o => o.Items)
    .Where(o => o.Status == OrderStatus.Active)
    .ToListAsync(ct);

---

Pattern 2: Query Splitting to Prevent Cartesian Explosion

When loading multiple navigation collections via Include(), EF Core generates a single query that can cause cartesian explosion.

The Problem

// Single query: produces Cartesian product of OrderItems x Payments
var orders = await db.Orders
    .Include(o => o.Items)      // N items
    .Include(o => o.Payments)   // M payments
    .ToListAsync(ct);
// Result set: N x M rows per order

The Solution

var orders = await db.Orders
    .Include(o => o.Items)
    .Include(o => o.Payments)
    .AsSplitQuery()
    .ToListAsync(ct);
// Executes 3 separate queries: Orders, Items, Payments

Global Default

options.UseNpgsql(connectionString, npgsql =>
    npgsql.UseQuerySplittingBehavior(QuerySplittingBehavior.SplitQuery));

Trade-offs

Approach	Pros	Cons
Single query (default)	Atomic snapshot, one round-trip	Cartesian explosion with multiple Includes
Split query	No Cartesian explosion, less data transfer	Multiple round-trips, no atomicity guarantee

Rule of thumb: Use AsSplitQuery() when including two or more collection navigations.

---

Pattern 3: Migration Management

CRITICAL: Always use EF Core CLI commands to manage migrations. Never manually edit migration files (except for custom SQL in Up()/Down()).

Creating Migrations

dotnet ef migrations add AddCustomerTable \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

dotnet ef migrations add AddCustomerTable \
    --context ApplicationDbContext \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

Removing Migrations

dotnet ef migrations remove \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

Applying Migrations

dotnet ef database update \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

dotnet ef database update AddCustomerTable \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

dotnet ef database update PreviousMigrationName \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

Generating SQL Scripts

dotnet ef migrations script \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api \
    --output migrations.sql

dotnet ef migrations script \
    --idempotent \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api

Migration Bundles for Production

dotnet ef migrations bundle \
    --project src/MyApp.Infrastructure \
    --startup-project src/MyApp.Api \
    --output efbundle \
    --self-contained

./efbundle --connection "Host=prod-db;Database=myapp;Username=deploy;Password=..."

Migration Best Practices

1. Always generate idempotent scripts for production (--idempotent flag)
2. Never call Database.Migrate() at startup in production -- use migration bundles or scripts
3. Keep migrations additive -- add columns with defaults, add tables, add indexes
4. Review generated code -- EF Core scaffolding can produce unexpected SQL
5. Use separate migration projects -- keep migrations in infrastructure project

Data Seeding

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<OrderStatus>().HasData(
        new OrderStatus { Id = 1, Name = "Pending" },
        new OrderStatus { Id = 2, Name = "Processing" },
        new OrderStatus { Id = 3, Name = "Completed" },
        new OrderStatus { Id = 4, Name = "Cancelled" });
}

---

Pattern 4: Dedicated Migration Service with Aspire

Separate migration execution from your main application.

Project Structure

src/
├── MyApp.AppHost/           # Aspire orchestration
├── MyApp.Api/               # Main application
├── MyApp.Infrastructure/    # DbContext and migrations
└── MyApp.MigrationService/  # Dedicated migration runner

MigrationWorker.cs

public class MigrationWorker : BackgroundService
{
    private readonly IServiceProvider _serviceProvider;
    private readonly IHostApplicationLifetime _hostApplicationLifetime;
    private readonly ILogger<MigrationWorker> _logger;

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("Migration service starting...");

        try
        {
            using var scope = _serviceProvider.CreateScope();
            var dbContext = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();

            await RunMigrationsAsync(dbContext, stoppingToken);

            _logger.LogInformation("Migration service completed successfully.");
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Migration service failed: {Error}", ex.Message);
            throw;
        }
        finally
        {
            _hostApplicationLifetime.StopApplication();
        }
    }

    private async Task RunMigrationsAsync(ApplicationDbContext dbContext, CancellationToken ct)
    {
        var strategy = dbContext.Database.CreateExecutionStrategy();

        await strategy.ExecuteAsync(async () =>
        {
            var pendingMigrations = await dbContext.Database.GetPendingMigrationsAsync(ct);

            if (pendingMigrations.Any())
            {
                _logger.LogInformation("Applying {Count} pending migrations...",
                    pendingMigrations.Count());

                await dbContext.Database.MigrateAsync(ct);

                _logger.LogInformation("Migrations applied successfully.");
            }
            else
            {
                _logger.LogInformation("No pending migrations. Database is up to date.");
            }
        });
    }
}

AppHost Configuration

var builder = DistributedApplication.CreateBuilder(args);

var postgres = builder.AddPostgres("postgres");
var db = postgres.AddDatabase("appdb");

var migrations = builder.AddProject<Projects.MyApp_MigrationService>("migrations")
    .WaitFor(db)
    .WithReference(db);

var api = builder.AddProject<Projects.MyApp_Api>("api")
    .WaitForCompletion(migrations)
    .WithReference(db);

---

Pattern 5: ExecutionStrategy for Transient Failures

Always use CreateExecutionStrategy() for operations that might fail transiently:

public async Task UpdateWithRetryAsync(Guid id, Action<Order> update)
{
    var strategy = _dbContext.Database.CreateExecutionStrategy();

    await strategy.ExecuteAsync(async () =>
    {
        var order = await _dbContext.Orders
            .AsTracking()
            .FirstOrDefaultAsync(o => o.Id == id);

        if (order is null) return;

        update(order);
        await _dbContext.SaveChangesAsync();
    });
}

With Transactions

var strategy = _dbContext.Database.CreateExecutionStrategy();

await strategy.ExecuteAsync(async () =>
{
    await using var transaction = await _dbContext.Database.BeginTransactionAsync();

    try
    {
        await _dbContext.SaveChangesAsync();
        await transaction.CommitAsync();
    }
    catch
    {
        await transaction.RollbackAsync();
        throw;
    }
});

Provider-Specific Configuration

// PostgreSQL
options.UseNpgsql(connectionString, npgsql =>
    npgsql.EnableRetryOnFailure(
        maxRetryCount: 3,
        maxRetryDelay: TimeSpan.FromSeconds(30),
        errorCodesToAdd: null));

// SQL Server
options.UseSqlServer(connectionString, sqlServer =>
    sqlServer.EnableRetryOnFailure(
        maxRetryCount: 3,
        maxRetryDelay: TimeSpan.FromSeconds(30),
        errorNumbersToAdd: null));

---

Pattern 6: Interceptors

EF Core interceptors allow cross-cutting concerns without modifying entity logic.

Audit Timestamp Interceptor

public sealed class AuditTimestampInterceptor : SaveChangesInterceptor
{
    public override ValueTask<InterceptionResult<int>> SavingChangesAsync(
        DbContextEventData eventData,
        InterceptionResult<int> result,
        CancellationToken ct = default)
    {
        if (eventData.Context is null)
            return ValueTask.FromResult(result);

        var now = DateTimeOffset.UtcNow;

        foreach (var entry in eventData.Context.ChangeTracker.Entries<IAuditable>())
        {
            switch (entry.State)
            {
                case EntityState.Added:
                    entry.Entity.CreatedAt = now;
                    entry.Entity.UpdatedAt = now;
                    break;
                case EntityState.Modified:
                    entry.Entity.UpdatedAt = now;
                    break;
            }
        }

        return ValueTask.FromResult(result);
    }
}

public interface IAuditable
{
    DateTimeOffset CreatedAt { get; set; }
    DateTimeOffset UpdatedAt { get; set; }
}

Soft Delete Interceptor

public sealed class SoftDeleteInterceptor : SaveChangesInterceptor
{
    public override ValueTask<InterceptionResult<int>> SavingChangesAsync(
        DbContextEventData eventData,
        InterceptionResult<int> result,
        CancellationToken ct = default)
    {
        if (eventData.Context is null)
            return ValueTask.FromResult(result);

        foreach (var entry in eventData.Context.ChangeTracker.Entries<ISoftDeletable>())
        {
            if (entry.State == EntityState.Deleted)
            {
                entry.State = EntityState.Modified;
                entry.Entity.IsDeleted = true;
                entry.Entity.DeletedAt = DateTimeOffset.UtcNow;
            }
        }

        return ValueTask.FromResult(result);
    }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Product>()
        .HasQueryFilter(p => !p.IsDeleted);
}

Registration

builder.Services.AddDbContext<AppDbContext>((sp, options) =>
    options.UseNpgsql(connectionString)
           .AddInterceptors(
               sp.GetRequiredService<AuditTimestampInterceptor>(),
               sp.GetRequiredService<SoftDeleteInterceptor>()));

builder.Services.AddSingleton<AuditTimestampInterceptor>();
builder.Services.AddSingleton<SoftDeleteInterceptor>();

---

Pattern 7: Compiled Queries

For queries executed very frequently:

public static class CompiledQueries
{
    public static readonly Func<AppDbContext, int, Task<Order?>>
        GetOrderById = EF.CompileAsyncQuery(
            (AppDbContext db, int orderId) =>
                db.Orders
                    .AsNoTracking()
                    .Include(o => o.Items)
                    .FirstOrDefault(o => o.Id == orderId));

    public static readonly Func<AppDbContext, string, IAsyncEnumerable<Order>>
        GetOrdersByCustomer = EF.CompileAsyncQuery(
            (AppDbContext db, string customerId) =>
                db.Orders
                    .AsNoTracking()
                    .Where(o => o.CustomerId == customerId)
                    .OrderByDescending(o => o.CreatedAt));
}

var order = await CompiledQueries.GetOrderById(db, orderId);

await foreach (var o in CompiledQueries.GetOrdersByCustomer(db, customerId)
    .WithCancellation(ct))
{
}

When to use: Queries that execute thousands of times per second. For typical CRUD, standard LINQ is sufficient.

---

Pattern 8: Bulk Operations

Use EF Core 7+ ExecuteUpdateAsync and ExecuteDeleteAsync:

// WRONG - Loads all entities into memory
var expiredOrders = await _db.Orders
    .Where(o => o.ExpiresAt < DateTimeOffset.UtcNow)
    .ToListAsync();

foreach (var order in expiredOrders)
{
    order.Status = OrderStatus.Expired;
}
await _db.SaveChangesAsync();

// CORRECT - Single SQL UPDATE statement
await _db.Orders
    .Where(o => o.ExpiresAt < DateTimeOffset.UtcNow)
    .ExecuteUpdateAsync(setters => setters
        .SetProperty(o => o.Status, OrderStatus.Expired)
        .SetProperty(o => o.UpdatedAt, DateTimeOffset.UtcNow));

await _db.Orders
    .Where(o => o.Status == OrderStatus.Cancelled && o.CreatedAt < cutoffDate)
    .ExecuteDeleteAsync();

---

Common Pitfalls

1. Forgetting to Update When NoTracking

// Silent failure - entity not tracked
var customer = await _db.Customers.FindAsync(id);
customer.Name = "New Name";
await _db.SaveChangesAsync(); // Does nothing!

// Explicit update
var customer = await _db.Customers.FindAsync(id);
customer.Name = "New Name";
_db.Customers.Update(customer);
await _db.SaveChangesAsync();

2. N+1 Query Problem

// N+1 queries - one query per order
var customers = await _db.Customers.ToListAsync();
foreach (var customer in customers)
{
    var orders = customer.Orders; // Lazy load triggers query
}

// Eager loading - single query
var customers = await _db.Customers
    .Include(c => c.Orders)
    .ToListAsync();

3. Tracking Conflicts

// Tracking conflict
var order1 = await _db1.Orders.AsTracking().FindAsync(id);
var order2 = await _db2.Orders.AsTracking().FindAsync(id);
order2.Status = OrderStatus.Shipped;
await _db2.SaveChangesAsync();

// Use single context or detach
_db1.Entry(order1).State = EntityState.Detached;

4. Querying Inside Loops

// Query per iteration
foreach (var orderId in orderIds)
{
    var order = await _db.Orders.FindAsync(orderId);
}

// Single query
var orders = await _db.Orders
    .Where(o => orderIds.Contains(o.Id))
    .ToListAsync();

---

Testing with EF Core

In-Memory Provider (Unit Tests Only)

var options = new DbContextOptionsBuilder<ApplicationDbContext>()
    .UseInMemoryDatabase(databaseName: Guid.NewGuid().ToString())
    .Options;

using var context = new ApplicationDbContext(options);

Real Database with TestContainers

var container = new PostgreSqlBuilder()
    .WithImage("postgres:16-alpine")
    .Build();

await container.StartAsync();

var options = new DbContextOptionsBuilder<ApplicationDbContext>()
    .UseNpgsql(container.GetConnectionString())
    .Options;

---

Agent Gotchas

1. Do not inject DbContext into singleton services -- use IDbContextFactory<T> instead.
2. Do not forget CancellationToken propagation -- pass ct to all async EF Core methods.
3. Do not use Database.EnsureCreated() alongside migrations -- use only in test scenarios.
4. Do not assume SaveChangesAsync is transactional across multiple calls -- wrap in explicit transaction.
5. Do not hardcode connection strings -- read from configuration.
6. Always pass validateAllProperties: true to Validator.TryValidateObject.

---

References

• EF Core performance best practices
• DbContext lifetime, configuration, and initialization
• EF Core interceptors
• EF Core migrations overview
• EF Core compiled queries
• EF Core connection resiliency