Question

I use VS2010 to generate a SQL Server Compact database with two simple tables.

Both have a column TheID (int). On one I set unique to true on the other not.

And I set primary key on this column.

CREATE TABLE [TestTab] (
  [TheID] int NOT NULL
, [TheVal] nvarchar(100) NOT NULL
);
GO

ALTER TABLE [TestTab] ADD CONSTRAINT [PK_TestTab] PRIMARY KEY ([TheID]);
GO

For the other (with unique set on the column) I get:

CREATE TABLE [TestTab2] (
  [TheID] int NOT NULL
, [TheVal] nvarchar(100) NOT NULL
);
GO

ALTER TABLE [TestTab2] ADD CONSTRAINT [PK_TestTab2] PRIMARY KEY ([TheID]);
GO

CREATE UNIQUE INDEX [UQ__TestTab2__00000000000033E9] ON [TestTab2] ([TheID] ASC);
GO

Next I use the SQL Server Compact Toolbox to create a datacontext.

Selecting data works fine – but when I try to update the code it breaks on dc.SubmitChanges().

Simply my WP7 application ends.

A try / catch doesn’t help.

TestTab tT = (from A in dC.TestTabs select A).FirstOrDefault();

if(tT != null) {
    tT.TheText += "1";
    dC.SubmitChanges();
}

If I drop the unique index, the code works fine.

Any ideas why this happens?

Manfred

Answer 1

It is a LINQ to SQL on Windows Phone bug… Your index is a duplicate (the primary key definition also adds an index) – see my blog post here: http://erikej.blogspot.com/2012/04/windows-phone-local-database-tip.html. To get auto generated values, setting a primary keys is not enough, ypou must define the column as IDENTITY as well.