如何更新实体框架中的子列表？

Question

这些是模型：

public class Contact
{
    public Contact() 
    {
        Emails = new List<Email>(); 
    }
    public int Id { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }
    public string Address { get; set; }
    public ICollection<Email> Emails { get; set; }

}
 public  class Email
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual int ContactId { get; set; }
}

在我的详细信息页面上，用户可以添加更多电子邮件、删除现有电子邮件……等等……或更改现有电子邮件。如何更新收藏？我试试这个：

    var contactFromDb = db.Contacts.Include("Emails").Include("Telephones").Where(x => x.Id == contact.Id).FirstOrDefault();

      contactFromDb.Address = contact.Address;
      contactFromDb.Name = contact.Name;
      contactFromDb.Surname = contact.Surname;
      contactFromDb.Telephones = contact.Telephones;
      contactFromDb.Emails = contact.Emails;

字符串属性更新得很好，我尝试以相同的方式更新集合，但我得到了重复的值。如何更新电子邮件？

Answer 1

首先删除已删除的电子邮件：

var contactFromDb = db.Contacts.Include("Emails").Include("Telephones").FirstOrDefault(x => x.Id == updatedContact.Id);
contactFromDb.Address = updatedContact.Address;
contactFromDb.Name = updatedContact.Name;
contactFromDb.Surname = updatedContact.Surname;

// Delete removed emails
var emailsToDelete = (from email in contactFromDb.Emails
                        let item = updatedContact.Emails.SingleOrDefault(i => i.Id == email.Id)
                        where item == null
                        select email).ToList();
if (emailsToDelete.Any())
{
    foreach (var email in emailsToDelete)
    {
        db.Entry(email).State = EntityState.Deleted;
    }
}

更新后编辑的电子邮件：

foreach (var email in updatedContact.Emails)
{
    // If id of an email is not equal to 0, it's not new email and it should be updated
    if (email.Id > 0)
    {
        var emailInDb = contactFromDb.Emails.Single(e => e.Id == email.Id);
        db.Entry(emailInDb).CurrentValues.SetValues(email);
        db.Entry(emailInDb).State = EntityState.Modified;
    }
}

最后通过调用db.SaveChanges()带有0将插入ID 的新电子邮件，您可以为Phones.