Entity Framework Core: ORM в .NET

1dotnet add package Microsoft.EntityFrameworkCore.SqlServer
2dotnet add package Microsoft.EntityFrameworkCore.Tools
3dotnet add package Microsoft.EntityFrameworkCore.Design

1public class Blog
2{
3    public int Id { get; set; }
4    public string Title { get; set; } = string.Empty;
5    public string Content { get; set; } = string.Empty;
6    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
7    
8    public ICollection<Post> Posts { get; set; } = new List<Post>();
9}
10
11public class Post
12{
13    public int Id { get; set; }
14    public string Title { get; set; } = string.Empty;
15    public string Content { get; set; } = string.Empty;
16    
17    public int BlogId { get; set; }
18    public Blog Blog { get; set; } = null!;
19    
20    public ICollection<Comment> Comments { get; set; } = new List<Comment>();
21}
22
23public class Comment
24{
25    public int Id { get; set; }
26    public string Author { get; set; } = string.Empty;
27    public string Text { get; set; } = string.Empty;
28    
29    public int PostId { get; set; }
30    public Post Post { get; set; } = null!;
31}

1public class AppDbContext : DbContext
2{
3    public DbSet<Blog> Blogs => Set<Blog>();
4    public DbSet<Post> Posts => Set<Post>();
5    public DbSet<Comment> Comments => Set<Comment>();
6
7    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }
8
9    protected override void OnModelCreating(ModelBuilder modelBuilder)
10    {
11        modelBuilder.Entity<Blog>(entity =>
12        {
13            entity.HasKey(e => e.Id);
14            entity.Property(e => e.Title).IsRequired().HasMaxLength(200);
15            entity.HasMany(e => e.Posts)
16                  .WithOne(e => e.Blog)
17                  .HasForeignKey(e => e.BlogId);
18        });
19
20        modelBuilder.Entity<Post>(entity =>
21        {
22            entity.HasKey(e => e.Id);
23            entity.HasMany(e => e.Comments)
24                  .WithOne(e => e.Post)
25                  .HasForeignKey(e => e.PostId);
26        });
27    }
28}

1// Создание
2var blog = new Blog { Title = "My Blog" };
3context.Blogs.Add(blog);
4await context.SaveChangesAsync();
5
6// Чтение с Include
7var blogs = await context.Blogs
8    .Include(b => b.Posts)
9    .ThenInclude(p => p.Comments)
10    .Where(b => b.Title.Contains("My"))
11    .OrderByDescending(b => b.CreatedAt)
12    .ToListAsync();
13
14// Обновление
15var blogToUpdate = await context.Blogs.FindAsync(1);
16if (blogToUpdate is not null)
17{
18    blogToUpdate.Title = "Updated Title";
19    await context.SaveChangesAsync();
20}
21
22// Удаление
23context.Blogs.Remove(blogToUpdate!);
24await context.SaveChangesAsync();

1# Создание миграции
2dotnet ef migrations add InitialCreate
3
4# Применение миграций
5dotnet ef database update
6
7# Откат миграции
8dotnet ef database update PreviousMigration
9
10# Генерация скрипта
11dotnet ef migrations script

1// Для read-only запросов
2var blogs = await context.Blogs
3    .AsNoTracking()
4    .Where(b => b.Title.Contains("My"))
5    .ToListAsync();

1var blogDtos = await context.Blogs
2    .Select(b => new BlogDto
3    {
4        Id = b.Id,
5        Title = b.Title,
6        PostCount = b.Posts.Count
7    })
8    .ToListAsync();