Entity-Framework-Core迁移与优化

1. 迁移命令

dotnet ef migrations add InitialCreate
dotnet ef database update
dotnet ef migrations remove  # 撤销上次迁移

2. 常见优化

2.1 N+1 问题

//  N+1 查询
var blogs = context.Blogs.ToList();
foreach (var blog in blogs) {
    var posts = blog.Posts.ToList();  // 每个博客一次查询
}

//  Eager Loading
var blogs = context.Blogs.Include(b => b.Posts).ToList();

2.2 选择性加载

// 只查询需要的列
var results = context.Users
    .Where(u => u.Active)
    .Select(u => new { u.Id, u.Name })
    .ToList();

2.3 批量操作

// 使用 EFCore.BulkExtensions
context.BulkInsert(entities);
context.BulkUpdate(entities);

2.4 分割查询

context.Blogs
    .Include(b => b.Posts)
    .AsSplitQuery()  // 拆分为多个 SQL 查询
    .ToList();