public class User
  {
    public int Id { get; set; }
    /// <summary>
    /// 账号
    /// </summary>
    public string Account { get; set; }
    /// <summary>
    /// 邮箱
    /// </summary>
    public string Email { get; set; }
    /// <summary>
    /// 昵称
    /// </summary>
    public string Nickname { get; set; }
    /// <summary>
    /// 头像
    /// </summary>
    public string AvatarId { get; set; }
    /// <summary>
    /// 记录插入时间
    /// </summary>
    public DateTime InsertTime { get; set; }
    /// <summary>
    /// 记录修改时间
    /// </summary>
    public DateTime UpdateTime { get; set; }
  }

　　　　　　　modelBuilder.Entity<User>().Property(u => u.Account)
        .IsRequired()
        .IsUnicode(false)
        .HasMaxLength(50);
      modelBuilder.Entity<User>().Property(u => u.Email)
        .IsRequired()
        .IsUnicode(false)
        .HasMaxLength(100);
      modelBuilder.Entity<User>().Property(u => u.Nickname)
        .IsUnicode(false)
        .HasMaxLength(50);
      modelBuilder.Entity<User>().Property(u => u.AvatarId)
        .IsOptional()
        .HasMaxLength(100);

[DbConfigurationType(typeof(MySqlEFConfiguration))]
  public class CustomDbContext : DbContext
  {
    public CustomDbContext()
      : base("name=Master")
    {
      
      this.Configuration.LazyLoadingEnabled = false; 
      //DropCreateDatabaseIfModelChanges
      //new DropCreateDatabaseAlways<CustomDbContext>()
      Database.SetInitializer<CustomDbContext>(null);
    }

    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
      base.OnModelCreating(modelBuilder);
      EntityConfiguration.Set(modelBuilder);
    }
}

using (CustomDbContext db = new CustomDbContext())
{
          User user = new User 
          {
            Id = 1,
            Email = "test@1622.com",
          };
          DbEntityEntry<User> entry = db.Entry<User>(user);
          entry.State = EntityState.Unchanged;
          entry.Property(t => t.Email).IsModified = true;

          int num = db.SaveChanges();
}

try
{
//执行代码
}
catch (DbEntityValidationException ex)
{
  var e = ex.EntityValidationErrors;
}
catch (Exception ex)
{
}

        using (CustomDbContext db = new CustomDbContext())
        {
          User user = new User 
          {
            Id = 1,
            Email = "test@1622.com",
            Account = "a"
          };
          DbEntityEntry<User> entry = db.Entry<User>(user);
          entry.State = EntityState.Unchanged;
          entry.Property(t => t.Email).IsModified = true;

          int num = db.SaveChanges();
        }    

        using (CustomDbContext db = new CustomDbContext())
        {
          User user = new User 
          {
            Id = 1,
            Email = "test@132.com",
          };
          DbEntityEntry<User> entry = db.Entry<User>(user);
          entry.State = EntityState.Unchanged;
          entry.Property(t => t.Email).IsModified = true;

          User user1 = new User
          {
            Id = 1,
            Email = "test@132.com",
          };
          DbEntityEntry<User> entry1 = db.Entry<User>(user1);
          entry1.State = EntityState.Unchanged;
          entry1.Property(t => t.Email).IsModified = true;

          int num = db.SaveChanges();
        }  

        using (CustomDbContext db = new CustomDbContext())
        {
          User user = new User 
          {
            Id = 1,
            Email = "test@132.com",
          };
          DbEntityEntry<User> entry = db.Entry<User>(user);
          entry.State = EntityState.Unchanged;
          entry.Property(t => t.Email).IsModified = true;

          DbEntityEntry<User> entry1 = db.Entry<User>(user);
          entry1.State = EntityState.Unchanged;
          entry1.Property(t => t.Email).IsModified = true;

          int num = db.SaveChanges();
        }

      using (CustomDbContext db = new CustomDbContext())
        {
          User user = new User 
          {
            //Id = 1,
            Email = "test@132.com",
          };
          DbEntityEntry<User> entry = db.Entry<User>(user);
          entry.State = EntityState.Unchanged;
          entry.Property(t => t.Email).IsModified = true;
          int num = db.SaveChanges();
        }  

using (CustomDbContext db = new CustomDbContext())
        {
          User user = new User
          {
            Id = 4,
            Email = "test@132.com",
            Nickname = "TestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateError"
          };
          DbEntityEntry<User> entry = db.Entry<User>(user);
          entry.State = EntityState.Unchanged;
          entry.Property(t => t.Email).IsModified = true;
          int num = db.SaveChanges();
        }