LINQ To SQL exception with Attach(): Cannot add an entity with a key that is already in use

Question

Consider this typical disconnected scenario:

load a Customer object from SQL Server using LINQ To SQL
user edits the entity, and the presentation tier sends back the entity modified.
the data layer, using L2S, must send the changes to SQL Server

Consider this LINQ To SQL query whose intention is to take a Customer entity.

Cust custOrig = db.Custs.SingleOrDefault(o => o.ID == c.ID); //get the original
db.Custs.Attach(c, custOrig); //we don't have a TimeStamp=True property
db.SubmitChanges();

DuplicateKeyException: Cannot add an entity with a key that is already in use.

alt text

Question

How can you avoid this exception?
What's the best strategy for updating an entity that does NOT have/want/need a timestamp property?

Sub-Optimal Workarounds

manually set each property in the updated customer to the orig customer.
spin up another DataContext

JustLoren · Accepted Answer · 2009-11-18 19:15:16Z

23

This has to do with the fact that your datacontext (db) cannot track the same entity more than once. See this post for more details on what's going on.

One of the obscure comments at the bottom of that post says to try:

public void Update(Customer customer)
{
  NorthwindDataContext context = new NorthwindDataContext();
  context.Attach(customer);
  context.Refresh(RefreshMode.KeepCurrentValues, customer);
  context.SubmitChanges();
}

Let me know how it works out for you, as the OP of that post says it worked out for him...

edited Nov 18, 2009 at 19:15

answered Nov 18, 2009 at 19:06

JustLoren

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2 Comments

p.campbell Over a year ago

+1; thanks! That did indeed work! I'll leave this question 'unanswered' for now, but this answer definitely solves the problem!

DamienG Over a year ago

As JustLoren says Attach is there for giving a context an entity it doesn't yet have - it can't be used to replace one. In a typical situation if you are getting an object back it is sometime later and will be attached to a new data context.

Jan Gerlinger · Accepted Answer · 2012-07-17 14:15:08Z

-4

Instead of creating a new context you could do this:

public void Update(Customer customer)
{
    Customer oldCustomer= db.Custs.First(c => c.ID == customer.ID);  //retrieve unedited 
    oldCustomer = customer;  // set the old customer to the new customer.
    db.SubmitChanges();  //sumbit to database
}

edited Jul 17, 2012 at 14:15

Jan Gerlinger

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answered Jul 17, 2012 at 13:06

Jostein Lie Sand

17

1 Comment

Haukman Over a year ago

That won't update the database, it will just change what the variable oldCustomer refers to.

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