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LINQ to SQL: how to remove an associated child object

I"m using LINQ to SQL in Visual Studio 2010. I have an object 'Client" which has an optional related object "Building". The Building objects are defined in a separate Building table. Each Client may live in one of the bulidings, or they might not. The Client table has a BuildingId column to identify the related Building. There is a foreign key relationship defined (see below).

There is no problem making the original assignment of a building. I just set the BuildingId and call SubmitChanges. But when a client already has a BulidingId, and I want to remove the building from the client, that's when I run into the error. I try code like this:

client.Building = null;
db.SubmitChanges();

This causes an error: The UPDATE statement conflicted with the FOREIGN KEY constraint "FK_Client_Building". The conflict occurred in database "MyDB", table "dbo.Building", column 'BuildingId'.

The same thing happens if I use a statement like:
client.BuildingId = null;

The foreign key relationship is defined as:
ALTER TABLE [dbo].[Client] WITH CHECK ADD CONSTRAINT [FK_Client_Building] FOREIGN KEY([BuildingId])
REFERENCES [dbo].[Building] ([BuildingId])
GO
ALTER TABLE [dbo].[Client] CHECK CONSTRAINT [FK_Client_Building]
GO

If I make the change manually in the database (from SQL Server Mgmt Studio), I can change the BuildingId column to NULL.

In LINQ to SQL, how am I supposed to remove the building from the client? I just want to change the BuildingId column to NULL.

Thanks,
Jeff

Fernando Soto

Hi jblindberg;

If you have a samll test database can you zip it up and upload to here?

Fernando

nmarun

FernandoSoto... do you ever sleep?Arun

Fernando Soto

Humm sleep, humm what is that?

jblindberg

ASKER

Fernando, here's the database. Does this format work for you?

Jeff
hs.zip

Fernando Soto

Hi Jeff;

Unable to restore what I think is a backup of your database with an error stating that it hast two families but only one was provided. The best way is just to zip the database file, .mdf, and the log file into one zip file.

Fernando

jblindberg

ASKER

OK, here's a zip of the .mdf file. Hope this will be what you need to look at this problem.

Jeff

HealthSetDB.zip

Fernando Soto

Hi Jeff;

I downloaded and was able to attach the DB to the server.

I created a new project, added a Entity Framework Model, and used the code snippet shown below and had no problem deleting the BuildingId from a Client record and save it.

Did you modify the model once you created it or did you just used all the default values?

Fernando

HealthSetEntities db = new HealthSetEntities();

Client client = (from c in db.Clients
                 where c.BuildingId == 4
                 select c).FirstOrDefault();

client.BuildingId = null;
db.SaveChanges();

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jblindberg

ASKER

I'm not using Entity Framework Model, I'm using LINQ to SQL. So I don't have a HealthSetEntities class.

I generated the dbml and associated designer.cs files using the tools in Visual Studio 2010.

I get the DataContext (System.Data.Linq.DataContext) this way:
HealthSetDataContext context = new HealthSetDataContext(Settings.HSetConnStringHelper());
(uses a helper method to return either the test or production connection string)

In the Client class, the Building property is defined like this:
this._Building = default(EntityRef<Building>);

I haven't made any changes to the designer.cs file, it's just as it was auto-generated.

Jeff

Fernando Soto

Hi Jeff;

I just also tried it using Linq to SQL with the code in the snippet below with no issues as well. Seeming you are still having issues please post the actual code you are using.

Fernando

DataClasses1DataContext db = new DataClasses1DataContext();

Client client = (from c in db.Clients
                 where c.BuildingId == 4
                 select c).FirstOrDefault();

client.BuildingId = null;
db.SubmitChanges();

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jblindberg

ASKER

OK, I figured out what was happening.
First, even though I thought I was setting the BuildingId to null, actually I was setting it to zero.
But when I tried actually set BuildingId to null (like your example above), I got the following exception when trying to set the Client.BuildingId property:

System.Data.Linq.ForeignKeyReferenceAlreadyHasValueException
Operation is not valid due to the current state of the object.
at HSet.HealthSet.Client.set_BuildingId(Nullable`1 value) in HealthSet.designer.cs:line 1250

Apparently LINQ to SQL wasn't happy about changing the BuildingId property to null when it already had a Building object loaded.

So next I tried setting the Building property itself to null, like the code below.
This made LINQ happy, and everything is now working.

Thanks for your help.
Jeff

if (buildingId == 0)
{
  if (c.Building != null)
  {
    c.Building = null; // NOTE nullify the Building object property, not the BuildingId
  }
}
else
{
  c.BuildingId = buildingId;
}
db.SubmitChanges();

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Fernando Soto

Hi jblindberg;

I believe you will find that is going to cause an issue. Because you are removing the reference to the Building table. For example if you do the following two lines of code after getting the Client with BuildingId of 4 :

client.Building = null;
db.SubmitChanges();

If you attempt to do this just after the above two line you most likely come accross an error.

client.BuildingId = 4;
db.SubmitChanges();

You should be nulling the Building and not the reference.

Fernando

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jblindberg

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Fernando Soto

OK Jeff