July 9, 2008 06:12am pdt

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1. naspinski 28,850
2. sjturner2 20,250
3. CarlVerret 17,064
4. Fernando... 8,700
5. Ceiled 6,500
6. CMYScott 5,750
7. TheLearn... 5,172
8. Praesidium 4,664
9. GreenGhost 4,150
10. emoreau 3,050
11. gardavis 3,000
12. ZachSmith 2,600
13. SteveH_UK 2,000
13. Smart_Man 2,000
13. vb_jonas 2,000
13. Koocurrent 2,000
13. primeMov... 2,000
13. JimFive 2,000
13. michtsoi 2,000
13. p_davis 2,000
13. REA_ANDREW 2,000
13. dstanley9 2,000
13. Rahu_ket... 2,000
13. vs1784 2,000
13. IndianOcean 2,000
13. SwissKnife 2,000
13. cottsak 2,000

03.31.2008 at 08:39AM PDT, ID: 23282867

	[x] Attachment Details

[x]

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9.1

Linq DataContext best practices...

Zones: Language Integrated Query - LINQ, Microsoft Visual C#.Net, .NET Framework 3.x versions

Hi,

I have a class that is currently designed to work as follows:

Customer c = Customer.GetByID(5);
c.Name = "John Smith";
c.Save();

I'm moving to linq, so I designed my Customer class as part of a DBML file called cc. So, my code now looks like this:
cc dataCtx = new cc();
var query = from cust in dataCtx.Customers where cust.ID = 5 select cust;
Customer c = query.First();
c.Name = "John Smith";
dataCtx.SubmitChanges();

This works, as long as I CREATE the DataContext, and update the customer all in the same place. But what if I write a static method called GetByID(id) like I have right now, then all if the "Getting" code would move INSIDE of the customer class, and I'd have to save the DataContext somewhere in order for it to be available when Save() is called. Save() would need to call context.SubmitChanges() - but unless I were to save it somewhere (like in the session or something), the context would be long gone by the time Save() gets called. Certainly it's a totally different scope in the code.

Any suggestions about how to move from my current model to the new linq environment? What are the "best practice" recommendations for deal with these "DataContexts" that are needed to effectively manage all of this linq data?

Thanks.

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Question Stats

Zone: Programming

Question Asked By: kalliopi

Solution Provided By: sjturner2

Participating Experts: 1

Solution Grade: A

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03.31.2008 at 02:32PM PDT, ID: 21249388

sjturner2:

The best practice for using Linq in ASP.NET is that to recreate the datacontext for each postback.

"A data context is a unit of work. It tracks changes and submits updates to the Db when flushed. Because of this you should only keep it around long enough to do the work ...but no longer."

These blogs should help you:

http://codebetter.com/blogs/ian_cooper/archive/tags/LINQ/default.aspx

Accepted Solution

03.31.2008 at 08:59PM PDT, ID: 21251168

kalliopi:

Thanks for the info. I guess my question is really, if I have an object that has been loaded via some datacontext, but that context is no longer accessible (different scope let's say) - how can the changes to that object updated back to the database? Or do I have to get a new instance of the object in order to update it. Does my question make sense?

04.01.2008 at 01:04AM PDT, ID: 21252055

sjturner2:

Yes, there is an Attach method on the datacontext to reattached a disconnected object. This link should explain it:
http://blogs.msdn.com/dinesh.kulkarni/archive/2007/10/08/attach-if-you-have-something-detached.aspx

if you don't want to use this then the other option is to refetch the original object and replay your changes to the fetched object.

04.01.2008 at 08:22AM PDT, ID: 21254823

kalliopi:

Hi siturner2,

Yeah - I tried the attach method and it generates an errors that the object was loaded using a different context.

I understand the "goal" of these datacontexts, but logistically I'm fairly well confused about how to actually implement it. Specifically, the link in the first suggestion says that you should avoid caching entities loaded with a datacontext - but that seems to make the whole system fairly useless.

What if I have a method

public User GetUserByID(int id) {
MyDB db = new MyDB();
var query = from user in db.Users where user.ID = id;
return query.FirstOrDefault();
}

So - in my code somewhere I say:

User u = GetUserByID(5);
u.Password = "foo";

Now I want to save my changes. The context used to load this object has gone out of scope, is there ANY way to update the object at this point?

Sorry - but I just don't understand the recommended "logistics" of managing the context (which you must have in order to SubmitChanges). I'm sure that there is a good way to do it, but I don't see how at this point...

ej

04.01.2008 at 08:58AM PDT, ID: 21255226

sjturner2:

You can attach the updated object to a different datacontext. You need to use the Attach method with asModified as the 2nd parameter and set this to true.

04.01.2008 at 12:27PM PDT, ID: 21257242

kalliopi:

I'll give that a try - thanks.

20080236-EE-VQP-29 / EE_QW_EXPERT_20070906