【ASP.NET Core】让 EF Core 生成更“合理”的 UPDATE 语句 – 东邪独孤

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; } = default!;
    public string? Major { get; set; }
}

public class DemoDbContext : DbContext
{
    public DemoDbContext(DbContextOptions opt)
        : base(opt)
    {

    }

    public DbSet Students { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity(ent =>
        {
            ent.ToTable("tb_students");
            // 初始数据
            ent.HasData(new Student { Id = 1, Name = "吴小车", Major = "挖矿" },
                new Student { Id = 2, Name = "李肺", Major = "攻城掠地" },
                new Student { Id = 3, Name = "赵逗逗", Major = "打磨芯片" },
                new Student { Id = 4, Name = "范统", Major = "悲观经济学" },
                new Student { Id = 5, Name = "贾仁亿", Major = "社会猪圈学" });
        });
    }
}

_ = await dbcontext.Students.ExecuteUpdateAsync(setter =>
{
    setter.SetProperty(stu => stu.Name, newStu.Name);
    setter.SetProperty(stu => stu.Major, newStu.Major);
});

 public async Task UpdateStudent(Student stu/*, string old*/)
 {
     var dbcontext = HttpContext.RequestServices.GetRequiredService();
     // 开始跟踪
     dbcontext.Students.Attach(stu);
     // 强行改变实体状态
     dbcontext.Students.Update(stu);

     // 提交更新
     _ = await dbcontext.SaveChangesAsync();
     return RedirectToAction("Index");
 }

UPDATE "tb_students" SET "Major" = @p0, "Name" = @p1
      WHERE "Id" = @p2
      RETURNING 1;

@model DB.Student

<form class="modal-dialog" method="post" asp-action="@nameof(HomeController.UpdateStudent)">
    <input type="hidden" asp-for="Id" />
    @{
            // 把旧的值序列为 JSON
            string json = JsonSerializer.Serialize(Model);
    }
    <input type="hidden" name="old" value="@json"/>
    <div class="modal-content">
        <div class="modal-header">
            <h5>编辑学生信息h5>
            <button type="button" class="btn-close" data-bs-dismiss="modal">button>
        div>
        <div class="modal-body">
            <div class="row mb-3">
                <label class="form-label" asp-for="Name">姓名：label>
                <input type="text" class="form-control" asp-for="Name" />
            div>
            <div class="row mb-3">
                <label class="form-label" asp-for="Major">专业：label>
                <input class="form-control" type="text" asp-for="Major" />
            div>
        div>
        <div class="modal-footer">
            <button type="button" data-bs-dismiss="modal" class="btn btn-secondary">取消button>
            <button type="submit" class="btn btn-primary">确定button>
        div>
    div>
form>

public async Task UpdateStudent(Student stu, string old)
{
    var dbcontext = HttpContext.RequestServices.GetRequiredService();
    // 开始跟踪
    dbcontext.Students.Attach(stu);
    var entry = dbcontext.Students.Entry(stu);
    // 反序列化
    var oldvals = JsonSerializer.Deserialize(old);
    // 重点：设置快照
    entry.OriginalValues.SetValues(oldvals!);
    // 提交更新
    _ = await dbcontext.SaveChangesAsync();
    return RedirectToAction("Index");
}

// 开始跟踪
var entry = dbcontext.Students.Attach(stu);
// 反序列化
var oldvals = JsonSerializer.Deserialize(old);
// 重点：设置快照
entry.OriginalValues.SetValues(oldvals!);
……

UPDATE "tb_students" SET "Major" = @p0
      WHERE "Id" = @p1
      RETURNING 1;