Linq to SQL and concurrency with Rob Conery repository pattern
- by David Hall
I have implemented a DAL using Rob Conery's spin on the repository pattern (from the MVC Storefront project) where I map database objects to domain objects using Linq and use Linq to SQL to actually get the data.
This is all working wonderfully giving me the full control over the shape of my domain objects that I want, but I have hit a problem with concurrency that I thought I'd ask about here. I have concurrency working but the solution feels like it might be wrong (just one of those gitchy feelings).
The basic pattern is:
private MyDataContext _datacontext
private Table _tasks;
public Repository(MyDataContext datacontext)
{
_dataContext = datacontext;
}
public void GetTasks()
{
_tasks = from t in _dataContext.Tasks;
return from t in _tasks
select new Domain.Task
{
Name = t.Name,
Id = t.TaskId,
Description = t.Description
};
}
public void SaveTask(Domain.Task task)
{
Task dbTask = null;
// Logic for new tasks omitted...
dbTask = (from t in _tasks
where t.TaskId == task.Id
select t).SingleOrDefault();
dbTask.Description = task.Description,
dbTask.Name = task.Name,
_dataContext.SubmitChanges();
}
So with that implementation I've lost concurrency tracking because of the mapping to the domain task. I get it back by storing the private Table which is my datacontext list of tasks at the time of getting the original task.
I then update the tasks from this stored Table and save what I've updated
This is working - I get change conflict exceptions raised when there are concurrency violations, just as I want.
However, it just screams to me that I've missed a trick.
Is there a better way of doing this?
I've looked at the .Attach method on the datacontext but that appears to require storing the original version in a similar way to what I'm already doing.
I also know that I could avoid all this by doing away with the domain objects and letting the Linq to SQL generated objects all the way up my stack - but I dislike that just as much as I dislike the way I'm handling concurrency.
