How can I immediately retrieve a newly added row's ID without any other uniquely identifying information available within the newly added data?

Question

I am adding a row to a table, MyModel, in a database and then creating a notification regarding that new row to another table. I need the ID of the newly created MyModel row to properly create my notification.

This is my code from my controller:

MyModel newMyModel = new MyModel
{
    Title = appliedCourse.Title,
};
db.MyModel.Add();

// I need code here that finds the MyModel.ID - but I do not know how to search for this MyModel 
// because MyModel.Title is not necessarily unique - the only necessarily unique piece of data 
// would be the MyModel.ID
new MyModel MyModelWithId = db.MyModel.Find(MyModel) // <- that does not work

Notification newNotification = new Notification
{
    Time = DateTime.Now,
    Link = Url.Action("Details", "MyModel", newMyModelWithId.MyModelID),
    ViewableBy = "Admin",
    Complete = false
};
db.Notification.Add(newNotification);
db.SaveChanges();

Is there any way to retrieve the newly created MyModel's ID?

I can think of possibly searching for the 'largest ID value' and returning that - but I'm not sure if that's the most effective way.

Is the ID even created at the point when I need it, or do I need to do a db.SaveChanges(); call before searching for it?

Would it be necessary to add a unique value to the MyModel so that I can query the database for it to acquire it's ID that way? (although the ID is already my unique value for future queries) I was thinking a DateTimeCreated value and I would search for it like this:

new MyModel MyModelWithId = db.MyModel.FirstOrDefault(
                o => o.TimeDateCreated == MyModel.TimeDateCreated);

Not sure if the DateTime method is very efficient either.

score 2 · Accepted Answer · answered May 04 '12 at 12:19

You won't get the ID of the row until after you've save the changes.

In your example you'd have to hit SaveChanges twice. Once to save MyModel and generate the ID, then to save newNotification with the URL.Action.

MyModel newMyModel = new MyModel
{
    Title = appliedCourse.Title,
};
db.MyModel.Add();

// Save first, let the DB generate the ID.  
// The DB generated ID will automatically load into the object you just saved.
db.SaveChanges(); 

Notification newNotification = new Notification
{
    Time = DateTime.Now,
    Link = Url.Action("Details", "MyModel",new { id = newMyModel.ID }),
    ViewableBy = "Admin",
    Complete = false
};
db.Notification.Add(newNotification);
db.SaveChanges();

Mind you, unless you've got a really compelling reason, I might generate the the Url.Action when the new notification is being displayed and not as part of the model itself. Instead, you could hold a reference and that way only save once. That being said, that's a rough guess without knowing your use case.

Works perfectly, thank you. It did not seem intuitive to me that the act of saving the changes to the database would update the var newMyModel in this context. Great thing to know. Thanks again. — Ecnalyr, May 04 '12 at 12:50

score 0 · Answer 2 · edited May 23 '17 at 12:11

If MyModel has a Notifications property or if Notification has a MyModel property (navigation properties EF4 Code First: how to add a relationship without adding a navigation property), you can rig the link between them by setting the object reference. Then when you call db.SaveChanges(), it does the right thing setting the ids for you. It appears that won't work for you in this case because you want to use the id in another way.

How can I immediately retrieve a newly added row's ID without any other uniquely identifying information available within the newly added data?

2 Answers2