I have pretty much standard EF 6.1 'create object in a database' code wrapped in transaction scope. For whatever reason the data persists in db after the transaction fails (to complete).
Code:
using (var db = this.Container.Resolve<SharedDataEntities>()) // << new instance of DbContext
{
using (TransactionScope ts = new TransactionScope())
{
SubscriptionTypes st = this.SubscriptionType.Value;
if (st == SubscriptionTypes.Lite && this.ProTrial)
st = SubscriptionTypes.ProTrial;
Domain domain = new Domain()
{
Address = this.Address.Trim(),
AdminUserId = (Guid)user.ProviderUserKey,
AdminUserName = user.UserName,
Description = this.Description.TrimSafe(),
DomainKey = Guid.NewGuid(),
Enabled = !masterSettings.DomainEnableControlled.Value,
Name = this.Name.Trim(),
SubscriptionType = (int)st,
Timezone = this.Timezone,
Website = this.Website.TrimSafe(),
IsPrivate = this.IsPrivate
};
foreach (var countryId in this.Countries)
{
domain.DomainCountries.Add(new DomainCountry() { CountryId = countryId, Domain = domain });
}
db.Domains.Add(domain);
db.SaveChanges(); // << This is the Saving that should not be commited until we call 'ts.Complete()'
this.ResendActivation(domain); // << This is where the Exception occurs
using (TransactionScope ts2 = new TransactionScope(TransactionScopeOption.Suppress))
{
this.DomainMembership.CreateDomainUser(domain.Id, (Guid)user.ProviderUserKey, user.UserName, DomainRoles.DomainSuperAdmin | DomainRoles.Driver);
ts2.Complete();
}
this.Enabled = domain.Enabled;
ts.Complete(); // << Transaction commit never happens
}
}
After SaveChanges() exception is thrown inside ResendActivation(...) so the changes should not be saved. However the records stay in database.
There is no other TransactionScope wrapping the code that I've pasted, it's triggered by an MVC Action call.
after more investigations, turns out that something - probably Entity Framework upgrade or database update process had put
Enlist=false;
into the database connection string. That effectively stops EF from picking up Transaction Scope.
So the solution is to set it to true, or remove it, I think by default it's true
Try using the transaction from the db instance it self, db.Database.BeginTransaction() if I recall it correctly instead of using the transaction scope.
using (var ts = db.Database.BeginTransaction())
{
..
}
Assuming that db is your entity framework context.
Context class by default support transactions. but with every new instance of context class, a new transaction will be created. This new transaction is a nested transaction and it will get committed once the SaveChanges() on the associated context class gets called.
In the given code it seems, we are calling a method that is responsible for creating a domain user i.e. CreateDomainUser and perhaps that has its own context object. thus this problem.
If this is the case(that this method has own context) the perhaps we don't even need TransactionScope here. We can simply pass the same context(that we are using before this call) to the function that is creating the domain user. We can then check for result of both operations and if they are successful, we simply need to call SaveChanges() method.
TransactionScope is usually needed when we are mixing ADO.NET calls with Entity framework. We can use it with context also, but it would be an overkill as the context class already has a transaction and we can simply use the same context to manage the transaction. If this is the case in the above code then the trick to fix the issue is to let the context class know that you want to use it with your own transaction. Since the transaction gets associated with the connection object in the scope, we need to use the context class with the connection that is being associated with the transaction scope. Also, we need to let the context class know that it cannot own the connection as it is being owned by the calling code. so we can do something like:
using (var scope = new TransactionScope(TransactionScopeOption.Required))
{
using (var conn = new SqlConnection("..."))
{
conn.Open();
var sqlCommand = new SqlCommand();
sqlCommand.Connection = conn;
sqlCommand.CommandText =
#"UPDATE Blogs SET Rating = 5" +
" WHERE Name LIKE '%Entity Framework%'";
sqlCommand.ExecuteNonQuery();
using (var context =
new BloggingContext(conn, contextOwnsConnection: false))
{
var query = context.Posts.Where(p => p.Blog.Rating > 5);
foreach (var post in query)
{
post.Title += "[Cool Blog]";
}
context.SaveChanges();
}
}
scope.Complete();
}
See: http://msdn.microsoft.com/en-us/data/dn456843.aspx
You should be able to use TransactionScope with EF, I know our projects do. However, I think you want the EF context instantiated inside the transaction scope -- that is, I believe you need to swap the outermost / first two using statements, as the answer from #rahuls suggests.
Even if it works the other way ... if you have a service / app / business layer method that needs to update several tables, and you want those updates to be atomic, you'd need to do it this way. So for the sake of consistency (and your own sanity), I would recommend transaction scope first, context second.
Related
Here is a very simplistic example of my current state:
using(var scope = new TransactionScope(TransactionScopeOption.Required, transactionScopeTimeout, TransactionScopeAsyncFlowOption.Enabled))
{
const string ConnectionString="server=localhost;username=;password=;enlist=false;Initial Catalog=blubber"
using(var myContext = new MyContext(ConnectionString))
{
var myTestObject = new TestObjectBuilder().WithId(1).Build();
myContext.Add(myTestObject);
myContext.SaveChanges();
}
// ...
using(var myContext = new MyContext(ConnectionString))
{
var myObj = myContext.MyObjects.Single(s => s.Id == 1); // This is the same object as above
}
}
I have a TransactionScope which will be used here, but in my connectionstring I explicitly say I don't wanna enlist my Entity Framework (6.2) Transactions.
The current behavior is that on the Single(s => s.Id == 1) Expression I get an error after 30 seconds (the default timeout) that the element could not be found.
First of all: Why do I not get a timeout-Exception or any SqlException? Second: Why is my data-row locked in the database?
Also via Sql Server Management Studio I can not query that exact row (only with the NOLOCK hint).
If I remove the TransactionScope or set the ISOLATION LEVEL to READ UNCOMMITED before the Single query everything works fine.
Also because of the Dispose of the transaction-scope at the end all data will be removed / rollbacked which also should not happen if I didn't enlist to this AmbientTransaction.
So my expected behavior is, that I get no lock and my data is persisted even the transactionscope is disposed and rollbacked. EF should ignore the transactionscope here.
Do I miss something critical here?
EDIT: I tried the same thing with NHibernate and here it works like a charm.
I have code that looks like the example below. There's an explicit transaction involved because of some database tomfoolery that needs to be done via a SP, and a save changes in the middle of it all. (Exception handling, rollbacks, etc.. omitted):
void OuterMethod(MyDatbase context)
{
using(var dbTrans = context.Database.BeginTransaction())
{
// some stuff, the save puts the data where the SP can see it
Stuff(context);
context.SaveChanges();
// now some SP stuff
context.Database.ExecuteSqlCommand(#"spFoo", params);
// more stuff
MoreStuff(context);
AlmostUnrelatedCode(context);
context.SaveChanges();
dbTrans.Commit();
}
}
Right now the method AlmostUnrelatedCode() -- which is only marginally related to the process above -- needs a nice, fast, disposable read-only context 99% of the time. I have a factory that will serve me up the right kind of context when I need it. The 1% of the time it's called from the middle of that block above.
MyDatabase localReadOnlyContext;
void AlmostUnrelatedCode(MyDatabase context)
{
if ( context.Database.CurrentTransaction != null )
{
// Must use the context passed or everything deadlocks :(
localReadOnlyContext = context;
disposeContextLater = false;
}
else
{
// I just want to do this all the time
localReadOnlyContext = _contextFactory.CreateReadOptimized();
disposeContextLater = true;
}
// Do many, many things with my read-optimized context...
// The Dispose() on the class will check for disposeContextLater
}
What I'd like to do is to get rid of that transaction check, and in fact not need to pass the outer context at all if I can help it.
What I've tried:
Just ignoring what's going on in the outer transaction and using the context I generate all the time. Problem: deadlocks.
Trying to get the outermost transaction into the EF context I create with the _contextFactory. Problem: EF context constructors don't allow you to pass an existing transaction; also Database.CurrentTransaction has no setter.
Pulling the whole transaction out into a TransactionScope that wraps everything up. Problem: the method OuterMethod passes in the context, and I don't have control of the caller.
What I can't try:
Dirty reads/nolock. AlmostUnrelatedCode() needs the data as written so far.
I'd rather not:
Just keep using the outer context while inside of AlmostUnrelatedCode. AlmostUnrelatedCode deals with a lot of data trees and that context gets fat and unhappy really fast. It pollutes its context with crap really fast, and I'd rather just dispose of it when I'm done.
you can prevent the deadlocks by using one connection for multiple contexts.
example
var efConnectionString = ConfigurationManager.ConnectionStrings["SomeEntities"].ConnectionString;
// note EntityConnection, not SqlConnection
using (var conn = new EntityConnection(efConnectionString)) {
// important to prevent escalation
await conn.OpenAsync();
using (var c1 = new SomeEntities(conn, contextOwnsConnection: false)) {
//Use some stored procedures etc.
count1 = await c1.SomeEntity1.CountAsync();
}
using (var c2 = new SomeEntities(conn, contextOwnsConnection: false)) {
//Use some stored procedures etc.
count2 = await c2.SomeEntity21.CountAsync();
}
}
in your case just get the connection from the context and reuse it
context.Database.Connection
Can't you separate things done in AlmostUnrelatedCode like this:
void AlmostUnrelatedCode()
{
var context = _contextFactory.CreateReadOptimized();
AlmostUnrelatedCode(context);
context.Dispose();
}
void AlmostUnrelatedCode(MyDatabase context)
{
// Do many, many things with context...
}
Now you can call AlmostUnrelatedCode(with param) from your OuterMethod. And maybe there is even more to be separated. Consider SOLID.
I try to understand how EF creates DB requests from object manipulations in code. My test scenario is simple:
using(var context = new Context())
{
var entity = context.Entities.First();
entity.A = "TST";
entity.B = "WrongValue";
context.SaveChanges();
}
My idea is to test, how EF deal with transaction.
Change A with correct value and change B with wrong value (non existing FK)
I track what happening in SQL Server DB.
I execute code and nothing change in DB, that was expected.
Strange part is that there are two independant SQL request and I don't understand how EF revert first one.
Both Entity Framework and EntityFramework core code are open source. You can check the code at
Entity Framework - Link
Entity Framework Core - Link
If you see the internal code of Save method (pasted the code snapshot below) then you can validate that it internally it creates a transaction if an external transaction is not provided.
internal int SaveChangesInternal(SaveOptions options, bool executeInExistingTransaction)
{
AsyncMonitor.EnsureNotEntered();
PrepareToSaveChanges(options);
var entriesAffected = 0;
// if there are no changes to save, perform fast exit to avoid interacting with or starting of new transactions
if (ObjectStateManager.HasChanges())
{
if (executeInExistingTransaction)
{
entriesAffected = SaveChangesToStore(options, null, startLocalTransaction: false);
}
else
{
var executionStrategy = DbProviderServices.GetExecutionStrategy(Connection, MetadataWorkspace);
entriesAffected = executionStrategy.Execute(
() => SaveChangesToStore(options, executionStrategy, startLocalTransaction: true));
}
}
ObjectStateManager.AssertAllForeignKeyIndexEntriesAreValid();
return entriesAffected;
}
So your below code will internally wrapped inside a transaction which you can validate in SQL Profiler..
using(var context = new Context())
{
var entity = context.Entities.First();
entity.A = "TST";
entity.B = "WrongValue";
context.SaveChanges();
}
However, SQL profiler does not start logging transaction so you need to configure that in trace setting. See the below screenshot of SQL profiler new Trace setting, here, I have checked Show All events. After that Transaction category is being displayed. You can subscribe for Begin Tran, Commit Tran and Rollback Tran events to validate transaction statements. When you will run your scenario, you can see that Begin and Rollback should be logged.
Will the below code rollback the changes if there are any exception while saving?
using (SampleEntities context = new SampleEntities())
{
//Code Omitted
context.EmpPercAdjustments.AddRange(pp);
context.SampleJobs.AddRange(sampleJobs);
context.SaveChanges();
}
Or
Do I need to use transaction?
using (SampleEntities context = new SampleEntities())
{
//Code Omitted
using (System.Data.Entity.DbContextTransaction tranc = context.Database.BeginTransaction( ))
{
try
{
context.EmpPercAdjustments.AddRange(pp);
context.SampleJobs.AddRange(sampleJobs);
context.SaveChanges();
tranc.Commit();
}
catch (Exception ee)
{
tranc.Rollback();
}
}
}
Are there any advantages of using one over the others?
Yes it will rollback correctly.
In this case, you do not need to run an explicit transaction, because there is one already created by Entity Framework.
Creating a transaction by calling context.Database.BeginTransaction() is good, if you want f.e. to get the Id of just inserted record, something like this:
using (SampleEntities context = new SampleEntities())
{
using (System.Data.Entity.DbContextTransaction trans = context.Database.BeginTransaction( ))
{
context.SampleJobs.Add(newJob);
context.SaveChanges();
var jobId = newJob.Id;
//do other things, then commit or rollback
trans.Commit();
}
}
In this case, after calling SaveChanges(), the changes made on context objects are applied (so you can read database generated Id of added object in your scope), but they still have to be commited or rolled back, because changes are only dirty written.
Defining an explicit transaction can also be useful, if you have multiple methods that can modify context objects, but you want to have a final say, if changes they made will be all commited or not.
It is well known that the database locks taken inside the transaction are released on the end of that transaction. So, in this code..
public static TransactionScope CreateTransactionScope()
{
return new TransactionScope(TransactionScopeOption.Required,
new TransactionOptions() { IsolationLevel = IsolationLevel.ReadCommitted });
}
Actually, in this one...
using (DataContext dataContext = new DataContext())
using (TransactionScope rootScope = CreateTransactionScope())
{
using (TransactionScope nested = CreateTransactionScope())
{
Ticket ticket = dataContext.ExecuteQuery<Ticket>(
"SELECT * FROM Tickets WITH (UPDLOCK) WHERE id={0}", ticketId).First();
nested.Complete();
}
// Will the lock be still ON here? Because I don't need him to be!
}
When exactly the row/page lock (UPDLOCK) will be released - after the disposing the nested transaction or the root one?
It will be released only after the root scope will exit the using block and will dispose.
The best way to learn this kind of stuff is by getting your hands dirty.
Create a simple database with table A and table B, each contains single column, name it "TimeStamp" and create simple console application that inserting timestamp (or any kind of value) and you can play with the transaction options and learn the behaviour.