EntityFrameworkCore 中的 Attach 方法

Attach 的坑

Model	Filed	Database Value	Console Value
User	Phone	[phone]	[phone]
User	Email	null	eeeeeee
User	Id	1	1

dbcontext.Users.Add(new User()
    {
        UserName = "test1",
        CreatedAt = DateTime.Now
        Phone = "[phone]"
    });
dbcontext.SaveChanges();

var user = new User()
{
    Id = 1,
    Phone = "[phone]",
    Email = "eeeeeeee"
};
dbcontext.Users.Attach(user); 
//上面語句會拋異常，原因是dbcontext 已經跟蹤了一個相同Id的實體，所以使用Attach注意當前的上下文

var user = new User()
{
    Id = 1,
    Phone = "[phone]",
    Email = "eeeeeeee",
    UpdatedAt = DateTime.Now
};
var entryEntity = dbContext.Users.Attach(user1);

//entryEntity.State = EntityState.Unchanged; 有沒有這句話結果是一樣的
entryEntity.Property(p => p.Phone).IsModified = true;
entryEntity.Property(p => p.Email).IsModified = false;
dbContext.SaveChanges();

//數據庫中只有明確標為`IsModified`為`true`的 `Phone`的值更改了，其余值保持不變

var item = dbContext.Users.FirstAsync().Result;
//item 的值和 user 中值完全相同 

var user = new User()
{
    Id = 1,
    Phone = "[phone]",
    Email = "eeeeeeee",
    UpdatedAt = DateTime.Now
};
var entryEntity = dbContext.Users.Attach(user1);

entryEntity.State = EntityState.Modified;
entryEntity.Property(p => p.Phone).IsModified = true;
entryEntity.Property(p => p.Email).IsModified = false;
dbContext.SaveChanges();

//數據庫中只有明確標為`IsModified`為`false`的 `Emial`的值沒有更改，其余值都會做更改

var item = dbContext.Users.FirstAsync().Result;
//item 的值和 user 中值完全相同 

var user = dbContext.Users.FirstAsync().Result;
var userTemp = new User { Id = 1 };
dbContext.Users.Attach(userTemp);
//報異常，原因同例1

var user = dbContext.Users.AsNoTracking().FirstAsync().Result;
var userTemp = new User { Id = 1 };
dbContext.Users.Attach(userTemp);
//不報異常