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NEW POST: Adding DbTransaction functionality to the Generic Controller

wuz — Tue, 13 Jan 2009 22:11:41 GMT

Adding DbTransaction functionality to the Generic Controller

Hi,

I really like this approach and so want to ensure that i am not messing up my architecture. In some cases i cannot realize the transactional aspect only with a single execution of DataContext.SubmitChanges() at the end, because the order - execution of the added commands is not guaranteed afaik. Let's assume I have PersonDetails and Person with a FK constraint, so PersonDetails has to be deleted first.

So in most cases this throws an FK exception:

EntityDetailsTable.DeleteAllOnSubmit(delDetails);
EntityTable.DeleteAllOnSubmit(delEntities);
SubmitChanges();

Would work but if i am very unlucky the entity survives without details if the db server crashes at the right second

EntityDetailsTable.DeleteAllOnSubmit(delDetails);
SubmitChanges();
EntityTable.DeleteAllOnSubmit(delEntities);
SubmitChanges();

Solution which came into my mind: Manually implemented transaction with DbTransaction Class.

I would create the instance of DbTransaction in my GenericController like:

protected DbTransaction trans = null;

try
{
// Open the connection
DataContext.Connection.Open();
trans = DataContext.Connection.BeginTransaction();
DataContext.Transaction = trans;

EntityDetailsTable.DeleteAllOnSubmit(delDetails);
EntityTable.DeleteAllOnSubmit(delEntities);

trans.Commit();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
// Rollback transaction
if (trans != null)
trans.Rollback();
}
finally
{

// Close the connection
if (DataContext.Connection.State == ConnectionState.Open)
DataContext.Connection.Close();
}

This code snippet compiles wihtout problems although the delete statements are not fired because we are dealing with multiple entities and therefore have to use TransactionScope:

using (TransactionScope scope = new TransactionScope(TransactionScopeOption.RequiresNew))
{
try
{
EntityDetailsTable.DeleteAllOnSubmit(delDetails);
SubmitChanges();
DataContext.ExecuteCommand("DELETE * FROM blabla"); // raise exception
EntityTable.DeleteAllOnSubmit(delEntities);
SubmitChanges();

}
catch (Exception ex)
{
//throw new Exception(ex.Message);
//ThrowHelper.ThrowBackupException("Finalizing occurs an error. The transcation will be rollback.");
//return false;
logger.LogError(ex);
}

scope.Complete();
}

In this case the details got deleted cause obviousle transactionscope can only handle on Submit changes.

So i am very thankful for any help!

NEW POST: What is the fastest way to get a scalar value back

tintin5 — Wed, 19 Nov 2008 19:27:19 GMT

What is the fastest way to get a scalar value

I am wondering about the most efficient way to get back 1 non key value from an entity.

Things I would consider are
1. pre compiled queries
2. Object Tracking
3. Creating a “new” entity.

See this interesting article from Sidar

http://www.sidarok.com/web/blog/content/2008/05/02/10-tips-to-improve-your-linq-to-sql-application-performance.html

NEW POST: How to use in NON ASP.NET code sections?

rbates — Wed, 05 Nov 2008 14:18:33 GMT

Hello all, this project has now moved to http://www.codeplex.com/MultiTierLinqToSql
The most recent version also has the method to discard the datacontext requested in this thread

NEW POST: Problem on Update

rbates — Wed, 05 Nov 2008 14:15:26 GMT

Hello rabindradalai, I can't reproduce this error but I think it is because the movId column is the primary key of the table. You might be better fetching the entity first with GetEntity(id) and then updating it.
If you have any other questions then post them on the CodePlex site:
http://www.codeplex.com/MultiTierLinqToSql

NEW POST: Problem on Update

rabindradalai — Mon, 03 Nov 2008 11:12:19 GMT

RTPeat wrote:
Found the bug, problem solved.

Hi RTPeat, what was the problem you are facing..and how did you solved it. is it similar to the one that i am facing below:

Hi,

I have cerated my own DBMovieController<TEntity> which is inherited from GenericController<TEntity, DBMovieDataContext> where TEntity : class

when i try to call the following code

tblMain manupdate = new tblMain();
manupdate.movID = "3";
manupdate.movTitle = "FANNA !";
manupdate.movRunTime = 30;
DBMovieController<tblMain>.Update(manupdate);

it throws following error, but my movID is not a identity column in tblMain.

Value of member 'movID' of an object of type 'tblMain' changed.
A member defining the identity of the object cannot be changed.
Consider adding a new object with new identity and deleting the existing one instead

please give some inputs..

NEW POST: Problem on Update

rabindradalai — Mon, 03 Nov 2008 11:01:22 GMT

Hi,

I have cerated my own DBMovieController<TEntity> which is inherited from GenericController<TEntity, DBMovieDataContext> where TEntity : class

when i try to call the following code

tblMain manupdate = new tblMain();
manupdate.movID = "3";
manupdate.movTitle = "FANNA !";
manupdate.movRunTime = 30;
DBMovieController<tblMain>.Update(manupdate);

it throws following error, but my movID is not a identity column in tblMain.

Value of member 'movID' of an object of type 'tblMain' changed.
A member defining the identity of the object cannot be changed.
Consider adding a new object with new identity and deleting the existing one instead

please give some inputs..

NEW POST: Question - Error handling

rbates — Thu, 30 Oct 2008 19:52:27 GMT

Hello beljakm, to answer your question, the way you should handle this is in the OnUpdated/OnInserted event of your GenericObjectDataSource using code like the following:

 protected void ProductDataSource_Updated(object sender, ObjectDataSourceStatusEventArgs e)
    {
        if (e.Exception != null)
        {
            //litError is a literal control I am using to display the error to the user
            litError.Text = e.Exception.Message;
            e.ExceptionHandled = true;
        }
    }

Basically you check if an exception has occurred, do something with it, probably show the details to the user, and then tell the GenericObjectDatasource that you've handled it. To use this you'll need to get version 1.7 as there was a bug in the way this worked in previous versions.
Note that I'm moving the code over to CodePlex, so you can now use svn to get the latest source, should be easier for everyone!
Rupert

NEW POST: Question - Error handling

beljakm — Tue, 21 Oct 2008 18:14:43 GMT

Hello,

I have probably posted my question in the wrong discussion group earlier, so I am re-posting it.

rbates - the solution is very elegant, and its evolving. However, here is a question:

Where and how do you handle events, e.g. OnLastNameChanged() in your person class? If I extend Person class, as shown below, and an exception is thrown, I keep getting error in GenericObjectDataSourceView because PropertyDescriptor, SetValue property does not handle ArgumentException. Should I somehow handle this in PersonController? Any easy way to get around this? This based on ScottGu's blog.

namespace DataLayer
{
public partial class Person
{
partial void OnLastNameChanged()
{
if (this.LastName=="")
throw new Exception("Error: Last Name cannot be empty.");
}
}
}
P.S.
The example below is trivial, and it is only for illustrative purposes. I would like to know what is the best way to handle DataContext events.

NEW POST: Using LINQ to sql in three tier architecture with ObjectDataSource and BusinessObject

beljakm — Sat, 18 Oct 2008 18:26:46 GMT

I have been rapidly getting into generics, and learning its powers. Examples shown here are great. However, here is a question:

Where and how do you handle events, e.g. OnLastNameChanged() in your person class? If I extend Person class, as shown below, and an exception is thrown, I keep getting error in GenericObjectDataSourceView because PropertyDescriptor, SetValue property does not handle ArgumentException. Should I somehow handle this in PersonController? Any easy way to get around this?

namespace DataLayer
{
public partial class Person
{
partial void OnLastNameChanged()
{
if (this.LastName=="")
throw new Exception("Error: Last Name cannot be empty.");
}
}
}
P.S.
The example below is trivial, and it is only for illustrative purposes. I would like to know what is the best way to handle DataContext events.

NEW POST: Sorting with IEnumerable data not supported

rbates — Sat, 11 Oct 2008 13:46:53 GMT

Tess wrote:
Hello. Great discussion. I ran into a problem with the sample project, however, which I don't see discussed elsewhere. I get the error "data source 'ProductDataSource' does not support sorting with IEnumerable data. Automatic sorting is only supported with DataView, DataTable, and DataSet."
Did anyone else see that? Fix that?
Cheers,
Tess

Hi Tess, the fix is to add the attribute SortParameterName="sortExpression" into the ProductDataSource. I don't know how that got broken in the example project but I'll update it now, thanks for pointing it out.

NEW POST: Sorting with IEnumerable data not supported

Tess — Fri, 26 Sep 2008 20:18:19 GMT

Hello. Great discussion. I ran into a problem with the sample project, however, which I don't see discussed elsewhere. I get the error "data source 'ProductDataSource' does not support sorting with IEnumerable data. Automatic sorting is only supported with DataView, DataTable, and DataSet."
Did anyone else see that? Fix that?
Cheers,
Tess

NEW POST: EntitySet property or seperate controller

rbates — Sun, 21 Sep 2008 22:35:04 GMT

I'd definitely go for option 1. Not that there's anything particularly wrong with option 2 it's just more code for no gain. Also if the child table only makes sense in the context of the parent table then it's better practice to deal primarily with that table.

NEW POST: Question - Error handling

tc — Thu, 18 Sep 2008 08:05:30 GMT

Hi rbates, I was thinking the same thing by implementing a static close method or alike dispose of the datacontext by request.

It is a little more verbose, but if I could overcome my other requirement using the static implementation then I would go with the static approach, however I cannot think of another way of doing this, unless you have some suggestions? I need to be able to use a controller(s) dynamically to insert and update (using reflection and configuration), i'm using your GenericController as the data layer component of a larger generic application i am working on.

The idea is to feed my generic business components with a controller (based on the GenericController class and an interface I have implemented) and using reflection I create/insert/update entities regardless of the type. I haven't been able to figure out a way to do this with the static approach, any ideas?

I've attached the interface I have implemented, which basically just enforces additional overloads to create and insert entity objects without having to know the type at compile time. I couldn't think of any other way to go about doing this without knowing the types at compile time. I've implemented CreateEntity methods in the GenericController class to create, insert and return the correct entity, including non-generic methods.

I would appreciate your thoughts on what I have done and if you think I should/could have done things different/better.

Cheer
TC

public interface IController
{
void Insert(object entity);
...

object CreateObject();
...

void SubmitChanges();
}

public class GenericController<TEntity, TDataContext> : IController, IDisposable ...
{
...
...
...

public void Insert(object entity)
{
Insert(entity as TEntity)
}

public TEntity CreateEntity()
{
TEntity entity = new TEntity();
Insert(entity)

return entity;
}

public object CreateObject() // Same as CreateEntity but couldn't overload because of existing definition
{
return CreateEntity() as object;
}
}

NEW POST: How to use in NON ASP.NET code sections?

DavidB — Thu, 18 Sep 2008 04:46:07 GMT

Hi,

Thanks for the framework - very helpful!

It would be handy to be able to undo changes made to the datacontext in non-asp.net applications. As far as I can see there is no way to discard changes made to tables in a datacontext without destroying it. What about a method in the genericcontroller to destroy the datacontext, so then the next time a DataContext is called a new one is created?

Thanks,
David.

NEW POST: Question - Error handling

rbates — Wed, 17 Sep 2008 18:31:51 GMT

Hi tc, I think the approach you suggest is fine, it makes the code a bit more verbose but that's just a cosmetic thing really. Another thought I had would be to allow the calling code to tell the controller to dispose of the datacontext when it needed to, this would be useful in a number of other scenarios as well so I'll probably add it in at some point.

NEW POST: EntitySet property or seperate controller

tc — Wed, 17 Sep 2008 16:49:36 GMT

Hi,

I'm torn on which approach I should use to select/insert/update the collection side of one-to-many relationships, should I have a single controller and use the EntitySet property to insert/update or should i define a seperate controller and use this to select/insert/update?

eg.

Option 1 - single controller using EntitySet property

Parent p = new Parent();
p.Children.Add(new Child());
p.Children.Add(new Child());
ParentController.Insert(p);

Option 2 - one controller per table

Parent p = new Parent();
ParentController.Insert(p);

Child c = new Child();
c.ParentID = p.Parent.ID;
ChildController.Insert(c)

c = new Child();
c.ParentID = p.Parent.ID;
ChildController.Insert(c)

I'm currently leaning towards option 1 as it just seems to work better, but in doing so I want to ensure that i'm not violating any architecural best practices.

Any thoughts?

Thanks
TC

NEW POST: Question - Error handling

tc — Wed, 17 Sep 2008 16:22:37 GMT

Hi,

I'm having similar issues when dealing with exceptions, i've been finding that pending inserts/updates stay cached until they are submitted but i don't want them to because after the exceptions are handled the generally the actions are retried and I get into more trouble because of duplicate inserts and updates.

I am using this purely in a winforms application so I think the underlying issue for me comes down to the lifespan of the datacontext, the way I am working around this at the moment is I have converted the GenericController from static to instance methods and properties so the datacontext has the same lifespan as the controller (as suggested in another post by rbates).

I've found this to work OK so far, is there anything I should be concerned about with this approach?

Cheers
TC

NEW POST: Using LINQ to sql in three tier architecture with ObjectDataSource and BusinessObject

SkyTracer — Tue, 16 Sep 2008 13:18:52 GMT

Advice::
http://blogs.msdn.com/mirceat/archive/2008/03/13/linq-framework-design-guidelines.aspx

NEW POST: Using LINQ to sql in three tier architecture with ObjectDataSource and BusinessObject

tc — Fri, 12 Sep 2008 02:56:33 GMT

Hi wuz,

Just wondering if you could give me a little more detail on your implementation as I need to do a very similar thing to model some one-to-many relationships.

Your advice would be much appreciated...

Thanks
TC

NEW POST: How to use in NON ASP.NET code sections?

tc — Fri, 12 Sep 2008 02:45:12 GMT

Hi rbates,

Thanks for the feedback, I guess my concern is that this application could have a lifetime from hours to days to possibly even weeks and i'm not sure that keeping the data context alive for this amount of time is a wise approach?

I'll try a few things and see how I go and post my finding here, I have a few options to try out so i don't think i will be short of ideas.

Thanks
TC