entity-framework-core

name	entity-framework-core
description	Master Entity Framework Core with best practices, performance optimization, and proper data access patterns

Entity Framework Core Skill

When to Use This Skill

Use this skill when you need to:

• Design EF Core models and relationships
• Optimize database queries for performance
• Implement proper data access patterns
• Handle migrations and database updates
• Troubleshoot EF Core performance issues

Prerequisites

• Understanding of relational database concepts
• Knowledge of C# and LINQ
• Familiarity with EF Core basics
• Basic understanding of database design

Step-by-Step Workflows

1. Model Design and Relationships

Input: Entity requirements and business rules
Output: Complete EF Core model with proper relationships

Design EF Core models with these requirements:

1. Define entities and properties
2. Configure relationships (one-to-many, many-to-many)
3. Set up primary and foreign keys
4. Add indexes for performance
5. Configure data annotations and fluent API

2. Query Optimization

Input: Slow EF Core queries or performance issues
Output: Optimized queries with better performance

Optimize these EF Core queries for better performance:

1. Identify N+1 query problems
2. Add proper includes and projections
3. Use AsNoTracking for read-only operations
4. Implement proper indexing
5. Optimize LINQ expressions

3. Migration Management

Input: Database schema changes
Output: Proper migrations with data preservation

Create EF Core migrations for these schema changes:

1. Generate migration files
2. Review migration code
3. Handle data transformations
4. Test migrations safely
5. Deploy with rollback strategy

Core EF Core Patterns

Model Configuration

// Entity with data annotations
public class Customer
{
    [Key]
    public int Id { get; set; }
    
    [Required]
    [StringLength(100)]
    public string Name { get; set; } = string.Empty;
    
    [EmailAddress]
    public string? Email { get; set; }
    
    [Column(TypeName = "decimal(18,2)")]
    public decimal Balance { get; set; }
    
    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
    
    // Navigation properties
    public virtual ICollection<Order> Orders { get; set; } = new List<Order>();
}

// Fluent API configuration
public class CustomerConfiguration : IEntityTypeConfiguration<Customer>
{
    public void Configure(EntityTypeBuilder<Customer> builder)
    {
        builder.HasKey(c => c.Id);
        
        builder.Property(c => c.Name)
               .IsRequired()
               .HasMaxLength(100);
               
        builder.Property(c => c.Email)
               .HasMaxLength(255);
               
        builder.Property(c => c.Balance)
               .HasPrecision(18, 2);
               
        builder.HasIndex(c => c.Email)
               .IsUnique()
               .HasDatabaseName("IX_Customer_Email");
               
        builder.Property(c => c.CreatedAt)
               .HasDefaultValueSql("GETUTCDATE()");
    }
}

Relationships

// One-to-many relationship
public class Order
{
    public int Id { get; set; }
    public string OrderNumber { get; set; } = string.Empty;
    public DateTime OrderDate { get; set; } = DateTime.UtcNow;
    
    // Foreign key
    public int CustomerId { get; set; }
    
    // Navigation properties
    public Customer Customer { get; set; } = null!;
    public virtual ICollection<OrderItem> OrderItems { get; set; } = new List<OrderItem>();
}

// Many-to-many relationship (EF Core 5+)
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; } = string.Empty;
    public decimal Price { get; set; }
    
    public virtual ICollection<OrderItem> OrderItems { get; set; } = new List<OrderItem>();
}

public class OrderItem
{
    public int Id { get; set; }
    public int OrderId { get; set; }
    public int ProductId { get; set; }
    public int Quantity { get; set; }
    public decimal UnitPrice { get; set; }
    
    public Order Order { get; set; } = null!;
    public Product Product { get; set; } = null!;
}

// Configuration
public class OrderConfiguration : IEntityTypeConfiguration<Order>
{
    public void Configure(EntityTypeBuilder<Order> builder)
    {
        builder.HasKey(o => o.Id);
        
        builder.Property(o => o.OrderNumber)
               .IsRequired()
               .HasMaxLength(50);
               
        builder.HasOne(o => o.Customer)
               .WithMany(c => c.Orders)
               .HasForeignKey(o => o.CustomerId)
               .OnDelete(DeleteBehavior.Restrict);
               
        builder.HasIndex(o => o.OrderNumber)
               .IsUnique();
    }
}

Query Optimization

Eager Loading

// Good: Use Include for related data
var orders = await _context.Orders
    .Include(o => o.Customer)
    .Include(o => o.OrderItems)
        .ThenInclude(oi => oi.Product)
    .Where(o => o.CustomerId == customerId)
    .ToListAsync();

// Better: Use Select for specific data
var orderDtos = await _context.Orders
    .Where(o => o.CustomerId == customerId)
    .Select(o => new OrderDto
    {
        Id = o.Id,
        OrderNumber = o.OrderNumber,
        OrderDate = o.OrderDate,
        CustomerName = o.Customer.Name,
        CustomerEmail = o.Customer.Email,
        Items = o.OrderItems.Select(oi => new OrderItemDto
        {
            ProductName = oi.Product.Name,
            Quantity = oi.Quantity,
            UnitPrice = oi.UnitPrice,
            TotalPrice = oi.Quantity * oi.UnitPrice
        }).ToList()
    })
    .ToListAsync();

AsNoTracking

// Read-only queries - use AsNoTracking
var customers = await _context.Customers
    .AsNoTracking()
    .Where(c => c.IsActive)
    .ToListAsync();

// For large datasets, use AsNoTrackingWithIdentityResolution
var customers = await _context.Customers
    .AsNoTrackingWithIdentityResolution()
    .Where(c => c.IsActive)
    .ToListAsync();

Split Queries

// For complex queries with multiple includes
var orders = await _context.Orders
    .Include(o => o.Customer)
    .Include(o => o.OrderItems)
        .ThenInclude(oi => oi.Product)
    .AsSplitQuery() // Split into separate SQL queries
    .Where(o => o.OrderDate >= startDate)
    .ToListAsync();

Raw SQL Queries

// For complex queries that can't be expressed in LINQ
var orders = await _context.Orders
    .FromSqlInterpolated($@"
        SELECT * FROM Orders 
        WHERE CustomerId = {customerId} 
        AND OrderDate >= {startDate}
        ORDER BY OrderDate DESC")
    .Include(o => o.Customer)
    .ToListAsync();

// Parameterized queries
var orders = await _context.Orders
    .FromSqlRaw("EXEC GetCustomerOrders @CustomerId, @StartDate", 
        customerId, startDate)
    .ToListAsync();

Performance Optimization

Indexing Strategy

public class ProductConfiguration : IEntityTypeConfiguration<Product>
{
    public void Configure(EntityTypeBuilder<Product> builder)
    {
        // Primary key index (automatic)
        builder.HasKey(p => p.Id);
        
        // Unique index for product SKU
        builder.HasIndex(p => p.Sku)
               .IsUnique()
               .HasDatabaseName("IX_Product_Sku");
               
        // Composite index for search
        builder.HasIndex(p => new { p.CategoryId, p.IsActive })
               .HasDatabaseName("IX_Product_Category_Active");
               
        // Full-text search index
        builder.HasIndex(p => p.Name)
               .HasMethod("FULLTEXT")
               .HasDatabaseName("IX_Product_Name_FullText");
    }
}

Query Batching

// EF Core automatically batches multiple queries
public async Task<CustomerDashboardDto> GetCustomerDashboardAsync(int customerId)
{
    var tasks = new[]
    {
        GetCustomerInfoAsync(customerId),
        GetRecentOrdersAsync(customerId),
        GetOrderStatisticsAsync(customerId)
    };
    
    var results = await Task.WhenAll(tasks);
    
    return new CustomerDashboardDto
    {
        Customer = results[0],
        RecentOrders = results[1],
        Statistics = results[2]
    };
}

private async Task<Customer> GetCustomerInfoAsync(int customerId)
{
    return await _context.Customers
        .AsNoTracking()
        .FirstOrDefaultAsync(c => c.Id == customerId);
}

Connection Resiliency

// Configure in DbContext
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder.UseSqlServer(
        connectionString,
        options => options
            .EnableRetryOnFailure(
                maxRetryCount: 3,
                maxRetryDelay: TimeSpan.FromSeconds(30),
                errorNumbersToAdd: null)
            .CommandTimeout(30));
}

Repository Pattern

public interface IRepository<T> where T : class
{
    Task<T?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
    Task<IReadOnlyList<T>> GetAllAsync(CancellationToken cancellationToken = default);
    Task<IReadOnlyList<T>> FindAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default);
    Task<T> AddAsync(T entity, CancellationToken cancellationToken = default);
    Task UpdateAsync(T entity, CancellationToken cancellationToken = default);
    Task DeleteAsync(T entity, CancellationToken cancellationToken = default);
}

public class Repository<T> : IRepository<T> where T : class
{
    protected readonly DbContext _context;
    protected readonly DbSet<T> _dbSet;
    
    public Repository(DbContext context)
    {
        _context = context;
        _dbSet = context.Set<T>();
    }
    
    public virtual async Task<T?> GetByIdAsync(int id, CancellationToken cancellationToken = default)
    {
        return await _dbSet.FindAsync(new object[] { id }, cancellationToken);
    }
    
    public virtual async Task<IReadOnlyList<T>> GetAllAsync(CancellationToken cancellationToken = default)
    {
        return await _dbSet.AsNoTracking().ToListAsync(cancellationToken);
    }
    
    public virtual async Task<IReadOnlyList<T>> FindAsync(
        Expression<Func<T, bool>> predicate, 
        CancellationToken cancellationToken = default)
    {
        return await _dbSet.AsNoTracking()
            .Where(predicate)
            .ToListAsync(cancellationToken);
    }
    
    public virtual async Task<T> AddAsync(T entity, CancellationToken cancellationToken = default)
    {
        await _dbSet.AddAsync(entity, cancellationToken);
        await _context.SaveChangesAsync(cancellationToken);
        return entity;
    }
    
    public virtual async Task UpdateAsync(T entity, CancellationToken cancellationToken = default)
    {
        _dbSet.Update(entity);
        await _context.SaveChangesAsync(cancellationToken);
    }
    
    public virtual async Task DeleteAsync(T entity, CancellationToken cancellationToken = default)
    {
        _dbSet.Remove(entity);
        await _context.SaveChangesAsync(cancellationToken);
    }
}

Unit of Work Pattern

public interface IUnitOfWork : IDisposable
{
    IRepository<Customer> Customers { get; }
    IRepository<Order> Orders { get; }
    IRepository<Product> Products { get; }
    Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
    Task BeginTransactionAsync(CancellationToken cancellationToken = default);
    Task CommitTransactionAsync(CancellationToken cancellationToken = default);
    Task RollbackTransactionAsync(CancellationToken cancellationToken = default);
}

public class UnitOfWork : IUnitOfWork
{
    private readonly DbContext _context;
    private IDbContextTransaction? _transaction;
    
    public UnitOfWork(DbContext context)
    {
        _context = context;
        Customers = new Repository<Customer>(_context);
        Orders = new Repository<Order>(_context);
        Products = new Repository<Product>(_context);
    }
    
    public IRepository<Customer> Customers { get; }
    public IRepository<Order> Orders { get; }
    public IRepository<Product> Products { get; }
    
    public async Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
    {
        return await _context.SaveChangesAsync(cancellationToken);
    }
    
    public async Task BeginTransactionAsync(CancellationToken cancellationToken = default)
    {
        _transaction = await _context.Database.BeginTransactionAsync(cancellationToken);
    }
    
    public async Task CommitTransactionAsync(CancellationToken cancellationToken = default)
    {
        if (_transaction != null)
        {
            await _transaction.CommitAsync(cancellationToken);
            await _transaction.DisposeAsync();
            _transaction = null;
        }
    }
    
    public async Task RollbackTransactionAsync(CancellationToken cancellationToken = default)
    {
        if (_transaction != null)
        {
            await _transaction.RollbackAsync(cancellationToken);
            await _transaction.DisposeAsync();
            _transaction = null;
        }
    }
    
    public void Dispose()
    {
        _transaction?.Dispose();
        _context.Dispose();
    }
}

Migration Best Practices

Migration Generation

# Add migration
dotnet ef migrations add AddCustomerTable --project MyProject.Data --startup-project MyProject.API

# Generate script
dotnet ef migrations script --project MyProject.Data --startup-project MyProject.API

# Update database
dotnet ef database update --project MyProject.Data --startup-project MyProject.API

Custom Migration Logic

public partial class AddCustomerData : Migration
{
    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.CreateTable(
            name: "Customers",
            columns: table => new
            {
                Id = table.Column<int>(type: "int", nullable: false)
                    .Annotation("SqlServer:Identity", "1, 1"),
                Name = table.Column<string>(type: "nvarchar(100)", maxLength: 100, nullable: false),
                Email = table.Column<string>(type: "nvarchar(255)", maxLength: 255, nullable: true),
                CreatedAt = table.Column<DateTime>(type: "datetime2", nullable: false, defaultValueSql: "GETUTCDATE()")
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Customers", x => x.Id);
                table.UniqueConstraint("UK_Customers_Email", x => x.Email);
            });
            
        migrationBuilder.CreateIndex(
            name: "IX_Customers_Email",
            table: "Customers",
            column: "Email",
            unique: true);
            
        // Seed data
        migrationBuilder.Sql(@"
            INSERT INTO Customers (Name, Email, CreatedAt) VALUES
            ('John Doe', '[e-mail]', GETUTCDATE()),
            ('Jane Smith', '[e-mail]', GETUTCDATE())
        ");
    }
    
    protected override void Down(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.DropTable(
            name: "Customers");
    }
}

Testing EF Core

In-Memory Database

public class OrderServiceTests
{
    private readonly DbContextOptions<ApplicationDbContext> _options;
    
    public OrderServiceTests()
    {
        _options = new DbContextOptionsBuilder<ApplicationDbContext>()
            .UseInMemoryDatabase(databaseName: Guid.NewGuid().ToString())
            .Options;
    }
    
    [Fact]
    public async Task CreateOrder_ValidOrder_ReturnsOrderId()
    {
        // Arrange
        await using var context = new ApplicationDbContext(_options);
        
        var customer = new Customer { Name = "John Doe", Email = "[e-mail]" };
        context.Customers.Add(customer);
        await context.SaveChangesAsync();
        
        var service = new OrderService(context);
        
        // Act
        var orderId = await service.CreateOrderAsync(new CreateOrderRequest
        {
            CustomerId = customer.Id,
            Items = new List<OrderItemRequest>
            {
                new() { ProductId = 1, Quantity = 2 }
            }
        });
        
        // Assert
        orderId.Should().BeGreaterThan(0);
        
        var order = await context.Orders.FindAsync(orderId);
        order.Should().NotBeNull();
        order.CustomerId.Should().Be(customer.Id);
    }
}

Common Pitfalls and Solutions

1. N+1 Query Problem

// Bad: N+1 queries
var orders = await _context.Orders.ToListAsync();
foreach (var order in orders)
{
    var customer = await _context.Customers.FindAsync(order.CustomerId); // N+1!
}

// Good: Eager loading
var orders = await _context.Orders
    .Include(o => o.Customer)
    .ToListAsync();

2. Tracking Unnecessary Entities

// Bad: Tracking read-only data
var customers = await _context.Customers.ToListAsync();

// Good: AsNoTracking for read-only
var customers = await _context.Customers
    .AsNoTracking()
    .ToListAsync();

3. Large Result Sets

// Bad: Loading all data
var allProducts = await _context.Products.ToListAsync();

// Good: Pagination
var products = await _context.Products
    .Skip(page * pageSize)
    .Take(pageSize)
    .ToListAsync();

Performance Monitoring

// Enable sensitive data logging in development
if (builder.Environment.IsDevelopment())
{
    builder.Services.AddDbContext<ApplicationDbContext>(options =>
        options.UseSqlServer(connectionString)
               .EnableSensitiveDataLogging()
               .EnableDetailedErrors()
               .LogTo(Console.WriteLine, LogLevel.Information));
}

// Query logging
public class ApplicationDbContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.LogTo(Console.WriteLine, LogLevel.Information);
    }
}

References

• EF Core Documentation
• Performance Best Practices
• Modeling Relationships

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This skill provides comprehensive guidance for Entity Framework Core development. Use it to build efficient, maintainable, and performant data access layers.