LINQ to SQL DuplicateKeyException problem - linq-to-sql

Question

I am using LINQ2SQL and I have a table called Customers with three columns
CustmerID, CustomerCode, CustomerName
CustmerID is Primery Key(and Identity=yes) and CustomerCode is just UniqueKey.
When I am updating this table using LINQ to SQL with duplicate customercode, I expect to see DuplicateKeyException but it is going into the general exception block instead of DuplicateKeyException block. Any ideas?
This is the code
public void Update(Customer cust)
{
using (LINQDemoDataContext db = new LINQDemoDataContext())
{
Customers entity = CustomerMapper.ToEntity(new Customers(), cust);
try
{
db.Customers.Attach(entity, true);
db.SubmitChanges();
}
//Concurrency Exception
catch (ChangeConflictException)
{
throw new ChangeConflictException("A concurrency error occurred!");
}
//duplicate record
catch (DuplicateKeyException)
{
throw new DuplicateKeyException(entity.CustmerCode);
}
//everything else
catch (Exception ex)
{
throw ex;
}
}
}
I am using VisualWebDeveloperExpress 2008 and SQL Express 2005.
Thanks & Regards,
Supremestar

Answer 1

If memory serves, and I may be wrong here, the DuplicateKeyException only fires for the primary key of the table.

Answer 2

I ran into this same problem, where the duplicate key objects were being retained in-memory even though they were not getting inserted into the database. I came up with the following work around:
MyDataContext _myDataContext = new MyDataContext(ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString);
public void AddObject(object myObject)
{
try
{
_myDataContext.Objects.InsertOnSubmit(myObject);
_myDataContext.SubmitChanges();
}
catch (System.Data.Linq.DuplicateKeyException ex)
{
_myDataContext = new MyDataContext(ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString);
throw ex;
You can then catch and handle (or ignore) the thrown DuplicateKeyException in the caller.
Another work around (albeit inefficient and memory hogging) is to create a new data context inside the AddObject method instead of using the shared data context instantiated as a class member.

Answer 3

I had the problem when adding an entity i got from a different DataContext.
(I bound the FooDb-Property of a BarDb-Entity to the SelectedValue from a DropDownList, which had a Table from a short-living DataContext as DataSource)
Let's look at the Linq2Sql internal Attach(entity):
private void attach_FooDb(FooDb entity){
this.SendPropertyChanging();
entity.BarDb = this;
}
And the BarDb Property set:
set{
BarDb previousValue = this._BarDb.Entity;
if (((previousValue != value) || (this._BarDb.HasLoadedOrAssignedValue == false))){
this.SendPropertyChanging();
if ((previousValue != null)){
this._BarDb.Entity = null;
previousValue.FooDb.Remove(this);
}
this._BarDb.Entity = value;
if ((value != null)){
value.FooDb.Add(this);
this._FK_Bar = value.ID;
}else{
this._FK_Bar = default(System.Guid);
}
this.SendPropertyChanged("BarDb");
}
}
So when attaching to a FooDb, the corresponding DataContext will recognize the BarDb Entity as newly created and added, even though it already existed in the Database.
You can solve it by:
only using a single DataContext or
creating a BarDb_safe Property in the submitting DataContext, which will first request the "equal" entity from the database, applies all properties and then attaches it the usual way.