EntityFramework 学习 一 Update Existing Entity using DBContext in Disconnected Scenario

using System;
using System.Collections.Generic;
    
public partial class Student
{
    public Student()
    {
        this.Courses = new HashSet<Course>();
    }
    
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public Nullable<int> StandardId { get; set; }
    public byte[] RowVersion { get; set; }
    
    public virtual Standard Standard { get; set; }
    public virtual StudentAddress StudentAddress { get; set; }
    public virtual ICollection<Course> Courses { get; set; }
}

using System;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Data.Entity.Core.Objects;
using System.Linq;
    
public partial class SchoolDBEntities : DbContext
{
    public SchoolDBEntities()
        : base("name=SchoolDBEntities")
    {
    }
    
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
            
    }
    
    public virtual DbSet<Course> Courses { get; set; }
    public virtual DbSet<Standard> Standards { get; set; }
    public virtual DbSet<Student> Students { get; set; }
    public virtual DbSet<StudentAddress> StudentAddresses { get; set; }
    public virtual DbSet<Teacher> Teachers { get; set; }
}
  

Student stud;
//1. Get student from DB
using (var ctx = new SchoolDBEntities())
{
    stud = ctx.Students.Where(s => s.StudentName == "New Student1").FirstOrDefault<Student>();
}

//2. change student name in disconnected mode (out of ctx scope)
if (stud != null)
{
    stud.StudentName = "Updated Student1";
}

//save modified entity using new Context
using (var dbCtx = new SchoolDBEntities())
{
    //3. Mark entity as modified
    dbCtx.Entry(stud).State = System.Data.Entity.EntityState.Modified;     
        
    //4. call SaveChanges
    dbCtx.SaveChanges();
}
    

1.从DB中获取存在是student

2.在context作用域之外设置studentname

3.使用Context.Entry()方法获取实体的DBEntityEntry，并更改实体状态为modified