LINQ Update Statement

Phil Critchley · April 12th, 2011, 02:14 PM

Hi

Does anyone know of any good web-based resources where I can get information on how to construct LINQ Update statements. I've done LINQ Select statements before with Imar's help but now I'm keen to look into LINQ Update statements instead of relying on standard SQL statements.

Thanks

Phil

Imar · April 12th, 2011, 02:58 PM

Hi there,

You may want to look at the 101 LINQ samples: http://msdn.microsoft.com/en-us/vcsharp/aa336746

However, Updates are not really part of LINQ; they are part of technologies that use LINQ such as LINQ to SQL or Entity Framework. Often all you need to do is call SaveChanges or SubmitChanges on a context that contains a modified entity,

What exactly are you trying to update?

Imar

Phil Critchley · April 12th, 2011, 03:10 PM

Hi Imar

Thanks for the reply. I want to update the status of a record in my SQL database which is by default set to '1' when the user interact which the system and triggers the update, I want to update the corresponding record and change its status to '3', etc.

The numerical status codes do correspond to associated status descriptions within a foreign key relationship between my tables.

I would prefer to use LINQ updates rather than standard SQL as it seems alot 'cleaner' to implement within my build if that make sense?

Thanks

Phil

Imar · April 12th, 2011, 03:42 PM

I guess it all depends on what you're doing. Here's a simple example using LINQ to SQL but the idea is the same for EF (not sure which one you're using):

Code:

 
using (PlanetWroxDataContext context = new PlanetWroxDataContext())
{
  Person myPerson  = context.People.Where(p => p.Id == 123).First();
  myPerson.Whatever = 3;  // Update the property
  context.SubmitChanges();
}

Does this help? If not, you need to be more concrete about what you're doing and how.

Cheers,

Imar

Phil Critchley · April 12th, 2011, 03:57 PM

Hi Imar

Thanks for the posting, it definately helps and explains what I'm after doing.

Thanks for your help.

Phil

Phil Critchley · April 12th, 2011, 05:45 PM

Hi Imar

I'm using Entity Framework. I can't get 'SubmitChanges' to implement with the EF and the only method I've found which is remotely the same is 'SaveChanges'. I'm assuming that both methods provide the same functionality and will update my backend SQL database?

Code:

Using myLiteratureCatalogue As New Model.LiteratureCataloguingEntities
            Dim existingStatus = (From publication In myLiteratureCatalogue.Publications Where publication.PublicationID = "" Select publication).First()

            ' Change the status of the publication.
            existingStatus.StatusID = (1)

            myLiteratureCatalogue.SaveChanges()

        End Using

Imar · April 13th, 2011, 03:00 AM

Hi Phil,

Quote:

I'm assuming that both methods provide the same functionality and will update my backend SQL database?

Yes, but in different frameworks. SubmitChanges is part of LINQ to SQL, while SaveChanges is part of Entity Framework 4. Both are similar ORM frameworks, where EF is getting more attention that L2S lately. I didn't know which one you were using so I mentioned both in my first post and then used L2S as an example later on.

Just realize that this code performs 2 queries: one to get the object, and another to update it. If you already had a reference to the said publication, you could update that instance instead.

Cheers,

Imar

Phil Critchley · April 13th, 2011, 05:09 AM

Hi Imar

Thanks very much for all the information you have provided me with. Its definately very beneficial to a novice like me who is just starting out with building ASP projects and not familiar with LINQ just the more traditional SQL.

Hopefully speak to you again soon

Phil

Imar · April 13th, 2011, 11:46 AM

You're welcome...

Imar

Phil Critchley · April 16th, 2011, 05:48 PM

Hi Imar

Is it possible to update a SQL Server database field with a NULL value using LINQ to Entities?

I'm trying to update a UniqueIdentifier field by getting the update to empty out the GUID. Is this possible?

Phil