N+1 query problem을 피하기 위해 가져올 속성을 .Include
으로 설정해야합니다.
public class User
{
public int Id { get; set; }
public string Name { get; set ;}
public virtual ICollection<Post> Posts { get; set; }
public virtual ICollection<Comment> Comments { get; set; }
}
public class Post
{
public int Id { get; set; }
public string Title { get; set ; }
public int AuthorId { get; set; }
public virtual User Author { get; set; }
public virtual ICollection<Comment> Comments { get; set; }
}
public class Comment
{
public int Id { get; set; }
public string Note { get; set ;}
public int PostId { get; set; }
public virtual Post Post { get; set; }
public int AuthorId { get; set; }
public virtual User Author { get; set; }
}
public class BlogContext : DbContext
{
public DbSet<User> Users { get; set; }
public DbSet<Post> Posts { get; set; }
public DbSet<Comment> Comments { get; set; }
}
다음이는 쿼리의 톤 할 것이라는 점에서 BAD입니다 :
using (var db = new BlogContext())
{
var user = db.Users.Single(u => u.Id=5)); // +1 query
foreach (var post in user.Posts) // N queries
{
var message = String.Format("{0} wrote {1}", user.Name, post.Title);
Console.WriteLine(message);
foreach (var comment in post.Comments) // N * M queries!
{
// and that .Author make N * M MORE!
var message = String.Format("\t{0} commented {1}", comment.Author.Name, comment.Note);
Console.WriteLine(message);
}
}
}
을 그리고 그것은 한 쿼리 할 수 있습니다 점에서이 좋은입니다 :
을
using (var db = new BlogContext())
{
var user = db.Users
.Single(u => u.Id=5))
.Include(u => u.Posts) // eliminates the N post queries
.Include(u => u.Posts.Comments) // eliminates the M comment queries
.Include(u => u.Posts.Comments.Author); // eliminates the M comment author queries
foreach (var post in user.Posts) // N queries
{
var message = String.Format("{0} wrote {1}", user.Name, post.Title);
Console.WriteLine(message);
foreach (var comment in post.Comments) // N * M queries!
{
// and that .Author make N * M MORE!
var message = String.Format("\t{0} commented {1}", comment.Author.Name, comment.Note);
Console.WriteLine(message);
}
}
}