Does an identity insert in EF 6 work for Guids?

Question

In reference to the selected answer in How can I get Id of inserted entity in Entity Framework? work for an Identity field that is a Guid?

Also, is there a way to just do a simple `SELECT @@IDENTITY' in a repository and interface setting?

Edit 1

I need to be able insert a record using the generic Repo method.

My model:

[Table(name: "Images")]
public class ImagesViewModel
{
    [Key, Required, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid RecordID { get; set; }

    [Column(TypeName = "image")]
    public byte[] MainImage { get; set; }

    public string MainImageMimeType { get; set; }

    [Column(TypeName = "image")]
    public byte[] ImageThumbnail { get; set; }

    public string ImageThumbnailMimeType { get; set; }

    public bool Enabled { get; set; }

    public bool PrimaryImage { get; set; }

    public bool RelatedImage { get; set; }

    public Guid? RelatedImageID { get; set; }

    public ImagesViewModel()
    {
        Enabled = true;
        PrimaryImage = true;
        RelatedImage = false;
    }
}

If I was doing a stored procedure, I could simply do a SELECT @@IDENTITY and return the value of the identity field or the newly inserted record.

Unfortunately, I am using code-first with a generic data repository. So far I have the following method (work in progress):

public virtual Guid Add<T>(T newItem) where T : class
{
    using (var context = new ApplicationDbContext())
    {
        context.Set<T>().Add(newItem);
        context.SaveChanges();

        context.Entry(newItem).

        return _ImagesViewModel.RecordID;
    };
}

So I guess I am asking, what is the proper way of doing this?

Edit 2

Here is an updated code snippet of the Add method (work in progress):

public virtual Guid Add<T>(T entity) where T : BaseEntity
{
    using (var context = new ApplicationDbContext())
    {
        DbSet dbSet = context.Set<T>();
        dbSet.Add(entity);
        context.SaveChanges();
        return entity.RecordID;
    }
}

public abstract class BaseEntity
{
    Guid RecordID { get; set; }
}

Your question is not clear (at least for me).Can you provide more info ? — Sampath, Aug 20 '16 at 16:01
SQL Server can **only** use `int` (or `bigint`) for `identity` columns - there is no such things as a "GUID identity".... and as a corollary - **no** that mechanism for `identity` does **not** work with GUIDs ... — marc_s, Aug 20 '16 at 16:20
OK, I understand that, however is there a way to return the Guid ID for a newly created record in eF6? — John Schultz, Aug 20 '16 at 16:24
The id will be updated automatically by EF once SaveChanges is called. As entity being reference type, you will get the updated id in the entity in your calling layer itself. You dont have to pass it from generic repository. EDIT : just noticed that you are having a new context in your generic repo; Im not sure whether this is the way repository pattern is to be implemented. IMO, the context should be same in the request scope to leverage the power of unit of work. — Developer, Aug 20 '16 at 17:30

Sampath · Answer 1 · 2016-08-20T17:31:38.893

2

I would like to suggest below mentioned implementation to you.I don't know whether is it possible to do it on your side or not.

public virtual Guid Add<T>(T entity) where T : BaseEntity
    {
        using (var context = new ApplicationDbContext())
        {
            DbSet dbSet = context.Set<T>();
            dbSet.Add(entity);
            context.SaveChanges();
            return entity.Id;
        }
    }

public abstract class BaseEntity
{
   public Guid Id { get; set;}
}

edited Aug 20 '16 at 17:31

answered Aug 20 '16 at 16:28

Sampath

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Cool, however, I am getting the following compile error: 'T' does not contain a definition for 'RecordID' and no extension method 'RecordID' accepting a first argument of type 'T' could be found (are you missing a using directive or an assembly reference?). This is on the return line specifically on RecordID – John Schultz Aug 20 '16 at 16:32
what are the values it returns when you type and put a dot after `newItem.` ? – Sampath Aug 20 '16 at 16:36
If your referring to the `context.Entry(newItem)`, there are at least 20 methods and parameters. – John Schultz Aug 20 '16 at 16:40
No,I'm asking about this line ..`return newItem.RecordID;//here it returns your GUID`. – Sampath Aug 20 '16 at 16:41
Ahh ok, I have the following available: `Equals`, `GetHashCode`, `GetType` and `ToString` – John Schultz Aug 20 '16 at 16:43
1

see this link : http://stackoverflow.com/questions/3547950/ef-generic-repository-get-id-from-new-inserted-generic-entity/5109428 – Sampath Aug 20 '16 at 16:51
I tried your suggestions and unfortunately those four methods I mentioned above are the only methods available. :( – John Schultz Aug 20 '16 at 17:06
do you have any compile time errors with above implementation ? – Sampath Aug 20 '16 at 17:08
OK,... had to change the type from int to Guid. I get the following error: `'GenericDataRepository.BaseEntity.RecordID' is inaccessible due to its protection level DataAccessLayer` – John Schultz Aug 20 '16 at 17:11
check the chat window :) – John Schultz Aug 20 '16 at 17:16
No,I mean your final implementation of the generic repository ? – Sampath Aug 20 '16 at 17:18
OK,Put that line as this `public Guid RecordID { get; set;}` – Sampath Aug 20 '16 at 17:31
Hey,What happened ? – Sampath Aug 21 '16 at 12:31
Sorry,... Fix one thing three things pop up. Unfortunately, it did not work, there are no compiler errors. – John Schultz Aug 21 '16 at 18:57
Have you found out the solution or what are the 3 things ? – Sampath Aug 22 '16 at 01:09
I know my solution closely matches yours, however there are some differences. And the three things were not related :). Thanks for your suggestion. – John Schultz Aug 22 '16 at 01:13

score 0 · Accepted Answer · answered Aug 21 '16 at 19:02

0

I was able to get it working. By changing the code in my BLL to just return the ID after the add as follows:

Change void Users_Add(SiteUsersModel _SiteUsersModel); to Guid Users_Add(SiteUsersModel _SiteUsersModel);

and

public void Users_Add(SiteUsersModel _SiteUsersModel)
{
    _IUsersRepository.Add(_SiteUsersModel);
}

to

public Guid Users_Add(SiteUsersModel _SiteUsersModel)
{
    Guid RecordID = new Guid();
    using (var context = new ApplicationDbContext())
    {
        context.SiteUsers.Add(_SiteUsersModel);
        context.SaveChanges();
        RecordID = _SiteUsersModel.RecordID;
    }
    return RecordID;
}

It seems to be good to go.

answered Aug 21 '16 at 19:02

John Schultz

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That's essentially identical to Sampath's answer of which you said "it did not work, there are no compiler errors". – Gert Arnold Aug 21 '16 at 19:21
Essentially, yes, exact, no. When traced, that code snippet would never get hit. – John Schultz Aug 21 '16 at 19:25
2

Doesn't that depends on how you embed it in your code? It's 1. create context, 2. add entity, 3. save, 4. return id. -- Same. – Gert Arnold Aug 21 '16 at 19:29
1

The essential idea is that after saving, the saved entity contains its new ID value. – Gert Arnold Aug 21 '16 at 19:31
I do see your point, however, when my add routine was commented out, the anove suggestion was never called – John Schultz Aug 21 '16 at 19:33

Does an identity insert in EF 6 work for Guids?

2 Answers2