EntityFramework 7 更新记录时出错

Question

Every time I want to updated my record, I am getting the following error:

"The instance of entity type 'User' cannot be tracked because another instance of this type with the same key is already being tracked. When adding new entities, for most key types a unique temporary key value will be created if no key is set (ie if the key property is assigned the default value for its type). If you are explicitly setting key values for new entities, ensure they do not collide with existing entities or temporary values generated for other new entities. When attaching existing entities, ensure that only one entity instance with a given key value is attached to the context."

Here is my code:

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();
}

The relevant classes:

User:

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; }
    }

Recipient:

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; }
    }

Contact Methods:

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; }
    }

This issue happens when I want to update a recipient, and it is another user doing the updating. So say user abcd did the last update, but now user zyx updates the record. So the Recipeint.LastUpdatedBy is set to the current Session User. When I do that, I get the above error. I cannot figure out how to get beyond this.

A small note: if I add this:

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

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

statement, and say user lastmodifiedby is set to user abc. Now User asfg updates this recipient for the first time, it goes through, and LastModifiedBy will be set to user asfg, but say user abc goes back and changes the recipient again, so lastmodifiedby goes back to abc, it fails, with the same error.

this is driving me nuts and I cannot figure it out!!!

Answer 1

I got the answer to this from Arthur Vickers at Microsoft . I wanted to share.

The code that sets the navigation property dbRecipient.LastModifiedBy is setting it to an entity instance that is not being tracked by the context. It seems like in this case the context is already tracking another instance for this same entity--presumably because it was brought in by the query through including the CreatedBy navigation.
EF can't track two instances of the same entity, which is why the exception is thrown, so you will need to give EF additional information here to know what to do. This can be complicated in the general case.
For example: if the tracked instance has properties that have been modified in the other instance.
However, assuming that isn't the case, then you can just lookup the instance that is being tracked and use it instead, For example:

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