AsNoTracking in EF Core

What is AsNoTracking?

AsNoTracking disables change tracking for a query, improving performance for read-only scenarios where you don’t need to update the retrieved entities.

Basic Usage

// With tracking (default)
var products = await context.Products.ToListAsync();

// Without tracking
var products = await context.Products
    .AsNoTracking()
    .ToListAsync();

Performance Benefits

// Benchmark comparison
// With tracking: ~100ms, 50MB memory
var tracked = await context.Products.ToListAsync();

// Without tracking: ~60ms, 30MB memory
var untracked = await context.Products
    .AsNoTracking()
    .ToListAsync();

When to Use AsNoTracking

Read-Only Queries

// API endpoints returning data
public async Task<IActionResult> GetProducts()
{
    var products = await context.Products
        .AsNoTracking()
        .ToListAsync();
    
    return Ok(products);
}

Reporting Queries

var report = await context.Orders
    .AsNoTracking()
    .Include(o => o.OrderItems)
    .Where(o => o.OrderDate >= startDate)
    .Select(o => new OrderReport
    {
        OrderId = o.Id,
        TotalAmount = o.TotalAmount,
        ItemCount = o.OrderItems.Count
    })
    .ToListAsync();

Large Dataset Queries

var allProducts = await context.Products
    .AsNoTracking()
    .ToListAsync(); // Better performance for large datasets

AsNoTrackingWithIdentityResolution

// Resolves duplicate entities in result set
var orders = await context.Orders
    .AsNoTrackingWithIdentityResolution()
    .Include(o => o.Customer)
    .Include(o => o.OrderItems)
        .ThenInclude(oi => oi.Product)
    .ToListAsync();

Global Configuration

// Set default tracking behavior
services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString)
           .UseQueryTrackingBehavior(QueryTrackingBehavior.NoTracking));

// Override for specific query
var products = await context.Products
    .AsTracking()
    .ToListAsync();

Limitations

// Cannot update untracked entities
var product = await context.Products
    .AsNoTracking()
    .FirstAsync(p => p.Id == 1);

product.Price = 99.99m;
await context.SaveChangesAsync(); // No update - entity not tracked

// Need to attach and set state
context.Products.Attach(product);
context.Entry(product).State = EntityState.Modified;
await context.SaveChangesAsync(); // Now updates

Best Practices

// 1. Use for read-only scenarios
var products = await context.Products
    .AsNoTracking()
    .ToListAsync();

// 2. Use with projections
var productDtos = await context.Products
    .AsNoTracking()
    .Select(p => new ProductDto
    {
        Id = p.Id,
        Name = p.Name,
        Price = p.Price
    })
    .ToListAsync();

// 3. Don't use when you need to update
var product = await context.Products
    .FirstAsync(p => p.Id == 1); // Keep tracking for updates
product.Price = 99.99m;
await context.SaveChangesAsync();

Performance Comparison

Summary

AsNoTracking improves performance by disabling change tracking for read-only queries. Use it for API responses, reports, and large datasets. Don’t use it when you need to update entities.