How do I save a transient object that already exists in an NHibernate session?

Question

I have a `Store` that contains a list of `Products`: ``` var store = new Store(); store.Products.Add(new Product{ Id = 1, Name = "Apples" }; store.Products.Add(new Product{ Id = 2, Name = "Oranges" }; Database.Save(store); ``` Now, I want to edit one of the `Products`, but with a transient entity. This will be, for example, data from a web browser: ``` // this is what I get from the web browser, this product should // edit the one that's already in the database that has the same Id var product = new Product{ Id = 2, Name = "Mandarin Oranges" }; store.Products.Add(product); Database.Save(store); ``` However, trying to do it this way gives me an error: a different object with the same identifier value was already associated with the session The reason is because the `store.Products` collection already contains an entity with the same Id. How do I get around this problem?

Accepted Answer

Instead of trying to merge the transient instance. Why not start with the actual instance...simply get the product by id, update the fields, and commit.

```
var product = session.Get<Product>(2);
product.Name = "Mandarin Oranges";
tx.Commit();
```

or the merge way...

```
var product = new Product{ Id = 2, Name = "Mandarin Oranges" };
var mergedProduct = (Product) session.Merge(product);
tx.Commit();
```

How do I save a transient object that already exists in an NHibernate session?

Solution

Problem