Entity Framework Core (EF Core) Notes

1. What is EF Core?

• Entity Framework Core (EF Core) is Microsoft’s modern Object-Relational Mapper (ORM) for .NET.
• It allows developers to work with a database using C# objects instead of SQL queries.
• Supports multiple databases: SQL Server, PostgreSQL, SQLite, MySQL, In-Memory DB, etc.
• Great for CRUD operations, enforcing relationships, and migrations.

2. Key Features

• LINQ to Entities

  • Write queries in C# with LINQ, which EF Core translates to SQL.

  • Example:

    var products = context.Products.Where(p => p.Price > 50).ToList();
    
    

• Change Tracking

  • Keeps track of object changes (Added, Modified, Deleted) and updates DB on SaveChanges().

• Migrations

  • Version control for your database schema.
  • Commands:
    • dotnet ef migrations add InitialCreate
    • dotnet ef database update

• Database Seeding

  • Insert initial test/admin data via OnModelCreating().

• Cross-Platform

  • Runs on Windows, macOS, Linux.

3. DbContext

• Central class for EF Core.

• Represents a session with the database.

• Defines entity sets as DbSet<T>.

• Example:

  public class AppDbContext : DbContext {
      public DbSet<Product> Products { get; set; }
      public DbSet<Order> Orders { get; set; }
  
      public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }
  
      protected override void OnModelCreating(ModelBuilder modelBuilder) {
          modelBuilder.Entity<Product>().HasKey(p => p.Id);
      }
  }