LINQ to SQL -

Post up the schema of the parent table.

if you look here, some other people have had your problem. http://forums.microsoft.com/msdn/ShowPost.aspx?PostID=3493504&SiteID=1

It appears that Linq2SQL has trouble mapping some foreign keys to some primary keys. One guy had a resolution, but I think you are already mapping to an IDENTITY column.

Since the database isn't being called I think you have to look at the mappings linq to sql is using. What does the Association look like? There should be an Association on both the parent and child classes. Take a look at the linq to sql Association between the two classes. The Association should have a ThisKey property. The cast that is failing is trying to cast the value of the property that ThisKey points to, I think. As far as I can tell there can be a problem when there is more than one key and the type of the first key does not match the type that ThisKey points too. I'm not sure how linq would determine what the first key is. From the looks of it you only have one key and one foreign key so that shouldn't be the problem, but the designer, if you are using it, has been known to get creative. I'm pretty much guessing, but this looks like something I've seen before.

Is this an example of this bug? If so, try running your code in .NET 4.0 now that the beta is out.

If, like me, you aren't ready to start using the beta, you may be able to work around the problem. The issue seems to be that LINQ does not properly support relationships defined on non-primary key fields. However, the term "primary key" does not refer to the primary key defined on the SQL table, but the primary key defined in the LINQ designer.

If you dragged your tables into the designer, then Visual Studio automatically inspects the primary key defined in the database and marks the corresponding class field(s) as "primary keys". However, these do not need to correspond to each other. You can remove the key Visual Studio chose for you, and pick another field (or group of fields). Of course, you need to make sure this is logical (you should have a unique constraint in the database on the field/fields you choose).

So I had 2 tables/classes related to eachother using an alternative key. The parent table had 2 keys: a surrogate primary key defined as an int, and an alternative natural key defined as a string. In the LINQ designer, I had defined the association using the alternative key, and I experienced the InvalidCastException whenever trying to update that association field on the child object. To work around this, I went into the LINQ designer, selected the int, and then changed the Primary Key property from True to False. Then I chose the string, and set it's Primary Key property to True. Recompiled, retested, and the InvalidCastException is gone.

Looking at your screen shot it looks like you may be able to fix your issue by changing the LINQ primary key on ResponseCode from ResponseCode.ID to ResponseCode.ResponseCodeTableID

ResponseCode rc = new ResponseCode() { SurveyQuestionName = "Q11", Code = 3, Description = "Yet another code" }; 

and:

INSERT INTO tblResponseCode (responseCodeTableId, surveyQuestionName, code, description) VALUES (13683, 'Q11', 3, 'Yet another code') 

Are not the same, you are not passing in the foreign key reference. Now, I'm huge n00b at LINQ2SQL, but I'd wager that LINQ2SQL is not smart enough to do that for you, and it expects it as the first parameter of the anonymous dictionary, and is trying to cast a string to an integer.

Just some ideas.

This block:

codebookVersion.ResponseCodes.Add(rc); db.SubmitChanges(); //exception gets thrown here 

Can you try InsertOnSubmit instead of Add? i.e.

codebookVersion.ResponseCodes.InsertOnSubmit(rc); 

I think Add is not meant to be used to insert records if my memory serves me right. InsertOnSubmit is the one to use.

To try and narrow down the culprit.

Have you tried replacing the anonymous dictionary with something like:

ResponseCode rc = new ResponseCode(); rc.SurveyQuestName = "Q11"; rc.Code = 3; rc.Description = "Yet Another Code"; 

I've yet to really work with .NET 3.5 yet (day job is still all 2.0), so I'm wondering if there is an issue with passing the data using the anonymous dictionary (The cases don't match the SQL Columns for one).

Yea, I've read that and other posts, but it always seems to involve someone linking up to a field that simply has a unique contraint. Or in this guy's case (which does sound exactly like mine), he didn't get a solution.

Here's the parent table:

tblResponseTable definition (which maps to CodebookVersion) COLUMN_NAME TYPE_NAME id int identity versionTag nvarchar responseVersionTag nvarchar 

versionTag does have a unique contraint on it, but that's not represented anywhere that I can see in the LINQ-to-SQL stuff - and since nothing ever goes to the database... still stuck.

Mike, I hear you. But no matter where I look, everything looks correct. I've checked and rechecked that the ResponseTableId is an int and that Id is an int. They're defined as such in the designer and when I go look at the generated code, everything again appears to be in order.

I've examined the associations. Here they are:

[Table(Name="dbo.tblResponseCode")] public partial class ResponseCode : ... ... [Association(Name="CodebookVersion_tblResponseCode", Storage="_CodebookVersion", ThisKey="ResponseCodeTableId", OtherKey="Id", IsForeignKey=true)] public CodebookVersion CodebookVersion { ... } [Table(Name="dbo.tblResponseCodeTable")] public partial class CodebookVersion : ... ... [Association(Name="CodebookVersion_tblResponseCode", Storage="_ResponseCodes", ThisKey="Id", OtherKey="ResponseCodeTableId")] public EntitySet<ResponseCode> ResponseCodes { ... } 

And a screenshot of the association in case that will help:

Any further thoughts?

ResponseCode rc = new ResponseCode() { CodebookVersion = codebookVersion, SurveyQuestionName = "Q11", Code = 3, Description = "Yet another code" }; db.ResponseCodes.InsertOnSubmit(rc); db.SubmitChanges(); 

You may want to check to see that any fields in your database tables which are set by the db server when inserting a new record have that reflected in the Linq to SQL diagram. If you select a field on the Linq to SQL diagram and view its properties you will see a field called "Auto Generated Value" which if set to true will ensure all new records take on the default value specified in the database.

LINQ to SQL has been deprecated, FYI - http://blogs.msdn.com/adonet/archive/2008/10/29/update-on-linq-to-sql-and-linq-to-entities-roadmap.aspx.

I ran into a very similar problem. I'll link you over to my wordy post: http://forums.asp.net/p/1223080/2763049.aspx

And I'll also offer a solution, just a guess...

 ResponseDataContext db = new ResponseDataContext(m_ConnectionString); CodebookVersion codebookVersion = db.CodebookVersions.Single(cv => cv.VersionTag == m_CodebookVersionTag); ResponseCode rc = new ResponseCode() { ResponseCodeTableId = codebookVersion.Id, SurveyQuestionName = "Q11", Code = 3, Description = "Yet another code" }; db.ResponseCodes.InsertOnSubmit(rc); db.SubmitChanges(); 

Somewhere in your object graph there is a conversion error, the underlying data model (or the Linq To SQL model) has changed. This is typically something like NVARCHAR(1) -> CHAR when it should be STRING, or something similar.

This error is not fun to hunt down, hopefully your object model is small.

We had a similar problem, caused by using non-integer keys. Details and hotfix number are here: https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=351358