Question

每次我想更新我的记录时，都会收到以下错误：

“无法跟踪实体类型'用户'的实例，因为另一个实例已经跟踪了具有相同密钥的此类型的实例。什么时候为大多数密钥类型添加新实体的唯一临时密钥值如果没有设置密钥，则将创建（即，如果分配了密钥属性）其类型的默认值）。如果您明确设置密钥新实体的值，确保它们不会与现有实体发生冲突为其他新实体生成的实体或临时值。什么时候附加现有实体，确保只有一个实体实例给定的键值附加到上下文中。“

这是我的代码：

public void SaveRecipient(Recipient myRecipient)
{
    if (myRecipient.RecipientGUID == Guid.Empty)
    {
        myRecipient.RecipientGUID = Guid.NewGuid();

        foreach (ContactMethod tmpCM in myRecipient.ContactMethods)
        {
            context.Entry(tmpCM.Type).State = EntityState.Unchanged;
        }

        context.Entry(myRecipient.LastModifiedBy).State = EntityState.Unchanged;
        context.Entry(myRecipient.Owner).State = EntityState.Unchanged;
        context.Entry(myRecipient.CreatedBy).State = EntityState.Unchanged;

        context.Recipients.Add(myRecipient);
    }
    else
    {
        var dbRecipient = context.Recipients
            .Include(a => a.ContactMethods).ThenInclude(t => t.Type)
            .Include(b => b.CreatedBy)
            .Include(c => c.LastModifiedBy)
            .Include(d => d.Owner).ThenInclude(o => o.Users)
            .FirstOrDefault(x => x.RecipientGUID == myRecipient.RecipientGUID);

        if (dbRecipient != null)
        {
            dbRecipient.FirstName = myRecipient.FirstName;
            dbRecipient.LastName = myRecipient.LastName;
            dbRecipient.Company = myRecipient.Company;

            foreach (ContactMethod tmpCM in myRecipient.ContactMethods)
            {
                var dbCM = dbRecipient.ContactMethods.FirstOrDefault(x => x.ContactMethodGUID == tmpCM.ContactMethodGUID);

                if (dbCM != null)
                {
                    dbCM.CountryCode = tmpCM.CountryCode;
                    dbCM.Identifier = tmpCM.Identifier;
                    dbCM.IsPreferred = tmpCM.IsPreferred;
                }
                else
                {
                    dbRecipient.ContactMethods.Add(tmpCM);
                }
            }

            //Only update this if it has changed.
            if (dbRecipient.LastModifiedBy.UserGUID != myRecipient.LastModifiedBy.UserGUID)
            {
                dbRecipient.LastModifiedBy = myRecipient.LastModifiedBy;
            }

            dbRecipient.LastModifiedOn = myRecipient.LastModifiedOn;
        }
    }

    context.SaveChanges();
}

相关课程：

用户：

public class User
    {
        [Key]
        public Guid UserGUID { get; set; }

        public string UserName { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string Email { get; set; }

        public bool IsSiteAdmin { get; set; }

        public bool IsActive { get; set; }

        public DateTime? CreatedOn { get; set; }

        public DateTime? LastLogin { get; set; }
    }

收件人：

public class Recipient
    {
        [Key]
        public Guid RecipientGUID { get; set; }

        [Required(ErrorMessage = "Please enter a Recipient's First Name.")]
        public string FirstName { get; set; }

        [Required(ErrorMessage = "Please enter a Recipient's Last Name.")]
        public string LastName { get; set; }

        public string Company { get; set; }

        public UserGroup Owner { get; set; }

        public virtual ICollection<ContactMethod> ContactMethods { get; set; }

        public User CreatedBy { get; set; }

        public DateTime CreatedOn { get; set; }

        public User LastModifiedBy { get; set; }

        public DateTime LastModifiedOn { get; set; }

        public bool IsActive { get; set; }
    }

联系方式：

public class ContactMethod
    {
        [Key]
        [HiddenInput(DisplayValue = false)]
        public Guid ContactMethodGUID { get; set; }

        [ForeignKey("ContactMethodTypeGUID")]
        public virtual ContactMethodType Type { get; set; }

        public string CountryCode { get; set; }

        [Required]
        public string Identifier { get; set; }

        public bool IsPreferred { get; set; }

        [ForeignKey("RecipientGUID")]
        public virtual Recipient Owner { get; set; }
    }

当我想要更新收件人时，会发生此问题，而另一个用户正在进行更新。所以说用户abcd做了最后一次更新，但现在用户zyx更新了记录。因此Recipeint.LastUpdatedBy设置为当前会话用户。当我这样做时，我得到上述错误。我无法弄清楚如何超越这个。

小记：如果我加上这个：

context.Entry(myRecipient.LastModifiedBy).State = EntityState.Unchanged;

if (dbRecipient.LastModifiedBy.UserGUID != myRecipient.LastModifiedBy.UserGUID)

中的

语句，并说用户lastmodifiedby设置为user abc。现在User asfg第一次更新此收件人，它会通过，LastModifiedBy将设置为user asfg，但是说用户abc返回并再次更改收件人，所以lastmodifiedby返回abc，它失败，出现同样的错误

这让我疯了，我无法弄清楚!!!

Answer 1

我从微软的 Arthur Vickers 得到了答案。我想分享。

设置导航属性dbRecipient.LastModifiedBy的代码将其设置为未被上下文跟踪的实体实例。在这种情况下，上下文似乎已经跟踪了同一实体的另一个实例 - 可能是因为它是通过包含CreatedBy导航的查询引入的。 EF无法跟踪同一实体的两个实例，这就是抛出异常的原因，因此您需要在此处提供EF附加信息以了解该做什么。在一般情况下，这可能很复杂例如：如果被跟踪的实例具有已在另一个实例中修改过的属性但是，假设情况并非如此，那么您只需查找正在跟踪的实例并使用它，例如：

if (dbRecipient.LastModifiedBy.UserGUID != myRecipient.LastModifiedBy.UserGUID)
{
    dbRecipient.LastModifiedBy = test.Set<User>().Find(myRecipient.LastModifiedBy.UserGUID);
}

EntityFramework 7更新记录时出错

1 个答案: