Update with LINQ help needed

[Nilla]

hi, I'm trying to write the simplest db application using C#, ASP and
LINQtosQL but cannot get the Update function to work. I have used the
codemodel from a sample called IntroToLinq.

My Insert and Get functions work, but the Update does nothing. No
errors are thrown and no changes are made.
Here's my code


In the DBHelper class:
public static void Update<T>(T obj, Action<T> update) where T : class
{
using (var db = GetDatabaseData())
{
db.GetTable<T>().Attach(obj);
update(obj);
db.SubmitChanges();
}
}

public static void UpdateMyclass(Myclass iss)
{
Update<Myclass>(iss, delegate(Myclass i)
{
i.ID = iss.ID;
i.Description = iss.Description;
i.Status = iss.Status;
});
}


In my codebehind for the page where I want to save:

Myclass theObj = MyDB.GetObjById(TextBox1.Text);
theObj.Description = TextBox2.Text;
theObj .ID = TextBox1.Text;

try
{
MyDB.UpdateMyclass (theObj);
............etc.





What is missing in this code? Is there another easy (working..) way
to save this object in the DB using Linq?
THANKS!

 

[Marc Gravell]

It looks like you are updating object from itself? So there won't be any
changes detected...

* You get/create "theObj" with some values
* You pass "theObj" to UpdateMyclass as "iss"
* UpdateMyclass creates a delegate, capturing "iss", that when given an
instance "i", updates "i" from "iss"
* UpdateMyclass calls Update<MyClass> passing "iss" as "obj", and the
delegate
* Update<T> gets a context, and attaches "obj"; it then invokes the
delegate and commits

Unwrap that, and the values got copied from the orignal instance to the
same instance...

What did you want to do?

Marc

 

[Marc Gravell]

By the way, you can "Attach(obj, true)", which will mark it as dirty. It
won't know *what* is dirty, though - so all values will get updated
(normally only changed values are UPDATEd).

Marc

 

[Nilla]

Thank you Marc!

The textbox TextBox2.Text contains a new description for the object,
thats where the difference from original object is.
I tried to use Attach(obj,true) but I got some errors then. (I will
try to recreated it to see what the problem was.)

 

[Nilla]

Ok, I got you now. Thanks for the help, it works fine.

 

[Marc Gravell]

I'm glad it is sorted ;-p

Marc