I'm writing some merge functionality in C# asp.NET MVC2. I am also using using Linq2SQL.
I have a block of code which calls two services, MessageService and UserService. These both in term call their appropriate repositories and make the amendments to the db. Each repository declares it's own instance of the repository so I'm thinking this will escalate the following code to DTC . The code is called from the AccountService, is this going to work at this level? And also is it bad practise to declare the DataContext at the top of every repository or should I pass the object around somehow? Thank you in advance
//Run the merge
try
{
using (TransactionScope scope = new TransactionScope())
{
// Update Messages to be owned by primary user
if (!_MessageService.UpdateCreatedById(MergeUser.UserID, CoreUser.UserID))
{
return false;
}
// Update Comments to be owned by primary user
foreach (var curComment in _MessageService.GetUserComments(MergeUser.UserID))
{
curComment.CreatedBy = CoreUser.UserID;
}
_MessageService.Save();
// Update Logins to be owned by primary user
foreach (var CurLogin in _UserService.GetLogins(MergeUser.UserID))
{
CurLogin.UserID = CoreUser.UserID;
}
_UserService.Save();
scope.Complete();
}
return true;
}
catch (Exception ex)
{
_ErrorStack.Add(ex.Message);
ErrorService.AddError(new ErrorModel("Portal", "WidgetRepository", ErrorHelper.ErrorTypes.Critical, ex));
return false;
}
Yes, This will work. TransactionScope leverages the Distributed transaction coordinator so it's capable of hosting Transactions beyond database levels.
Recommended practice for DataContext lifecycle is to restrict it to a unit-of-work.
I have two constructors on my repositories, one that takes a data context and one that does not (which then instatiates it's own). This means that I can create repositories using a shared data context as required.
My service classes then take a repository object in their constructor, so I can instantiate several services using repositories that are sharing a data context, if so required.
Related
I've read multiple questions similar to this one but none are exactly my situation.
Using linq-to-sql I insert a new record and submit changes. Then, in the same web request, I pull that same record, and update it, then submit changes. The changes are not saved. The DatabaseContext is the same across both these operations.
Insert:
var transaction = _factory.CreateTransaction(siteId, userId, questionId, type, amount, transactionId, processor);
using (IUnitOfWork unitOfWork = UnitOfWork.Begin())
{
transaction.Amount = amount;
_transactionRepository.Add(transaction);
unitOfWork.Commit();
}
Select and Update:
ITransaction transaction = _transactionRepository.FindById(transactionId);
if (transaction == null) throw new Exception(Constants.ErrorCannotFindTransactionWithId.FormatWith(transactionId));
using (IUnitOfWork unitOfWork = UnitOfWork.Begin())
{
transaction.CrmId = crmId;
transaction.UpdatedAt = SystemTime.Now();
unitOfWork.Commit();
}
Here's the unit of work code:
public virtual void Commit()
{
if (_isDisposed)
{
throw new ObjectDisposedException(GetType().Name);
}
_database.SubmitChanges();
}
I even went into the designer.cs file and put a breakpoint on the field that is being set but not updated. I stepped through and it entered and execute the set code, so the Entity should be getting "notified" of the change to this field:
public string CrmId
{
get
{
return this._CrmId;
}
set
{
if ((this._CrmId != value))
{
this.OnCrmIdChanging(value);
this.SendPropertyChanging();
this._CrmId = value;
this.SendPropertyChanged("CrmId");
this.OnCrmIdChanged();
}
}
}
Other useful information:
ObjectTracking is enabled
No errors or exceptions when second SubmitChanges is called (just silently fails update)
SQL profiler shows insert and select but not the subsequent update statement. Linq-To-Sql is not generating the update statement.
There is only one database, one database string, so the update is not going to another database
The table has a primary key.
I don't know what would cause Linq-To-Sql to not issue the update command and not raise some kind of error. Perhaps the problem stems from using the same DataContext instance? I've even refreshed the object from the database using the DataContact.Refresh method before it is pulled for the update, but that didn't help.
I have found what is likely to be the root cause. I am using Unity. The initial insert is being performed in a service class with a PerWebRequest lifetime. The select and update is happening in a class with a Singleton lifetime. So my assumption that the DataContext instances are the same was incorrect.
So, in my class with the Singleton lifetime, I get a fresh instance of the database repository and perform the update and no problem.
Now I still don't know why the original code didn't work and my approach could still be considered more a workaround than a solution, but it did solve my problem and hopefully will be useful to others.
Suppose I have to different methods and I place them in the transaction scope.
But every method open it's connection. so I need to enable MSDTC service in windows server.
but it is a shared hosting server and i can not enable it.
class Debit
{
public void InsertA()
{
//InsertCode
}
}
class Credit
{
public void InsertB()
{
// InsertCode
}
}
using (TransactionScope ts = new TransactionScope(TransactionScopeOption.Required))
{
DebitBAL debit = new DebitBAL();
CreditBAL credit = new CreditBAL();
debit.InsertA();
credit.InsertB();
ts.complete();
}
I use entity framework for my statements.
is it a good idea using transaction scope in a shared hosting server?
See this link for how to use transaction scopes with entity framework
In this link , explained for three cases in which transaction scope is being used to show rollback when an error occurs during an update of multiple entities:
1: when you have multiple save calls to the context;
2: when you have single save with multiple object;
3: and transactions across multiple contexts.
I'll preface this question with the following: I know there are a million posts on the internet about the old "An object with the same key already exists in the ObjectStateManager" issue. My scenario is a bit more complicated, I think.
I have a UnitOfWork class which creates a DbContext and passes it to any repository which is called. The pattern I'm using closely follows the Unit of Work tutorial on the ASP.NET site. Unlike the tutorial, my repositories take in Business entities, map them to data entities, and perform some CRUD action. My Business logic only works with Business entities. Here is what I'm trying to do in a sample Business Manager class:
_unitOfWork.Repository.Add(entity);
_unitOfWork.Save(); // context.SaveChanges() under the hood
...Perform some operations on the model...
_unitOfWork.Repository.Update(entity);
_unitOfWork.Save();
Here is a sample Update method from the repository:
public virtual void Update(entity)
{
var dataEntity = // map from business entity to data;
_context.Entry(dataEntity).State = EntityState.Modified;
}
It obviously fails on the last line. Here is where my confusion sets in:
The entity's State is Detached
When I attempt to change the State to Modified or Unchanged, it gives me the ObjectStateManager exception above.
When I attempt to detach the entity from the context (((IObjectContextAdapter)_context).ObjectContext.Detach(entity);) I get an exception about how the entity is not attached to the context, therefore, it cannot detach it. Very confusing (something fundamental I'm missing, for sure).
Many other posts suggest I make a database call, update that entity in the repository, then _unitOfWork.Save(). I don't like this approach. I shouldn't need to make an unnecessary network call to update an entity.
The Update method in the repository needs to handle two scenarios: 1) updating an entity which is not currently tracked by the context, and 2) updating an entity which IS currently tracked by the context. The second piece is what I'm struggling with.
Any help or insight is appreciated.
Thanks!
This means that there already is an object attached to the context with the same key as the new dataEntity. The existing object and the new entity both represent the same entry in the database but they are two different objects.
This may indicate that the lifespan of your _context is too long, but that's hard to judge from your code. It is certain though that the context was previously used to fetch an entity from the database that is subsequently duplicated by var dataEntity = ....
You may have to shorten the lifespan of the context, I can't tell. If you think it's OK you may want to use the Local collection to check whether the entity is already there. That will save the database round trip that Find may still make.
I found a hybrid solution which appears to work:
public virtual void Update(TB entity)
{
var dataEntity = Mapper.Map<TB, TD>(entity);
var pkey = _dbSet.Create().GetType().GetProperty("Id").GetValue(dataEntity);
var entry = _context.Entry(dataEntity);
if (entry.State == EntityState.Detached)
{
var attachedEntity = _dbSet.Find(pkey);
if (attachedEntity != null)
{
var attachedEntry = _context.Entry(attachedEntity);
attachedEntry.CurrentValues.SetValues(dataEntity);
}
else
{
entry.State = EntityState.Modified;
}
}
else
{
entry.State = EntityState.Modified;
}
}
I am develloping a web form that has a wizard with 4 steps:
On each step I'me creating new entities generated from a database.
The problem is that being a wizzard, the user can change the properties of the controls that will originate the values to be stored.
So I need to release the created entity objects or return that entity values to the original rows stored on the database.
How can I do this.
Should'n it work if I set each created entity object to null?
By the way this is how I'm doing it:
entities = new Entities();
...
Client client = new Client();
client.name = tbxName.text
...
entities.SaveChanges();
entities.Connection.Close();
So If this code is executed on the 2nd wizard part of a wizard of 3 parts and I go back and fowrward through this set more the once the client creating runs more than once, so there's my problem.
So how can I unCreate it :-P
Thannks!!!
If you are building wizard you must manage it as single operation. It means that you have to store built entity graph in the session and save it only if whole wizard is completed and confirmed. Your step logic also must check if related data are already present in the entity graph and use them instead of creating new one.
If your using Entity Framework, why not implement the Unit Of Work pattern? Each part of your wizard builds the UoW and the "final step" commits the unit of work.
There was an article called "The Unit Of Work Pattern And Persistence Ignorance" in MSDN magazine a few years ago that explains the concept.
This is the way I do it:
1- Create a place where you can manage your Session variables :
public class SessionObjects { }
2- I save my ObjectContext in the Session so I create a property to manage it in the mentioned class :
public static ObjectContextEntities ObjectContextEntities
{
get
{
return (ObjectContextEntities)HttpContext.Current.Session["ObjectContextEntities"];
}
set
{
HttpContext.Current.Session["ObjectContextEntities"] = value;
}
}
3- Initialize the ObjectContext on the wizard's start and dispose it on its end:
void StartWizard()
{
SessionObject.ObjectContextEntities = new ObjectContextEntities();
}
void StartWizard()
{
SessionObject.ObjectContextEntities = new ObjectContextEntities();
}
void EndWizard()
{
((ObjectContextEntities)SessionObject.ObjectContextEntities).Dispose();
}
4- To save wizard result to the database you can call:
void SaveWizard()
{
((ObjectContextEntities)SessionObject.ObjectContextEntities).SaveAllChanges();
}
5- To reset wizard simply call EndWizard then StartWizard .
I guess you know how to manage your ObjectEntity objects and in the ObjectContext so you can continue from here by your self ..
I'm developing an application that uses SQLite as the primary data storage method. I have two processes running for my app using an alternate entry point.
I need to access the same DB from the two different processes but as we all now SQLite is not like a server DB engine, it can only be accessed once at a time.
I wanted to know if there is a way to kind of "lock" the DB when it's being accessed by other process so that if the second process tries to acces the DB at the same time, it would wait until the first process finishes and then try to access it again.
How can this issue be treated?
If you have not already, create a class that abstracts your database access out and store it in the RuntimeStore. From wherever you are going to interface with SQLite, get a reference to that class using the GUID you stored it with (RuntimeStore.get(long)) and synchronize the class however you would normally (member object lock, synchronized methods).
Do NOT just use the Wikipedia style singleton pattern as it is not a true singleton across processes on this platform.
See:
http://www.blackberry.com/developers/docs/5.0.0api/net/rim/device/api/system/RuntimeStore.html
Sample:
class SQLManager {
private static long GUID = 0xa178d3ce564cae69L; // hash of com.stackoverflow.SQLManager
private SQLManager() {
// ctor stuff here
}
public static SQLManager getInstance() {
RuntimeStore rs = RuntimeStore.getRuntimeStore();
SQLManager instance = rs.get(GUID);
if (instance == null) {
instance = new SQLManager();
rs.put(GUID, instance);
}
return instance;
}
}
You're still using the singleton "pattern" per se, but you're storing the object instance in the RuntimeStore on first getInstance call, and subsequently pulling it form the RuntimeStore - using a GUID that you specify.