I am currently getting this error:
System.Data.SqlClient.SqlException: New transaction is not allowed because there are other threads running in the session.
while running this code:
public class ProductManager : IProductManager
{
#region Declare Models
private RivWorks.Model.Negotiation.RIV_Entities _dbRiv = RivWorks.Model.Stores.RivEntities(AppSettings.RivWorkEntities_connString);
private RivWorks.Model.NegotiationAutos.RivFeedsEntities _dbFeed = RivWorks.Model.Stores.FeedEntities(AppSettings.FeedAutosEntities_connString);
#endregion
public IProduct GetProductById(Guid productId)
{
// Do a quick sync of the feeds...
SyncFeeds();
...
// get a product...
...
return product;
}
private void SyncFeeds()
{
bool found = false;
string feedSource = "AUTO";
switch (feedSource) // companyFeedDetail.FeedSourceTable.ToUpper())
{
case "AUTO":
var clientList = from a in _dbFeed.Client.Include("Auto") select a;
foreach (RivWorks.Model.NegotiationAutos.Client client in clientList)
{
var companyFeedDetailList = from a in _dbRiv.AutoNegotiationDetails where a.ClientID == client.ClientID select a;
foreach (RivWorks.Model.Negotiation.AutoNegotiationDetails companyFeedDetail in companyFeedDetailList)
{
if (companyFeedDetail.FeedSourceTable.ToUpper() == "AUTO")
{
var company = (from a in _dbRiv.Company.Include("Product") where a.CompanyId == companyFeedDetail.CompanyId select a).First();
foreach (RivWorks.Model.NegotiationAutos.Auto sourceProduct in client.Auto)
{
foreach (RivWorks.Model.Negotiation.Product targetProduct in company.Product)
{
if (targetProduct.alternateProductID == sourceProduct.AutoID)
{
found = true;
break;
}
}
if (!found)
{
var newProduct = new RivWorks.Model.Negotiation.Product();
newProduct.alternateProductID = sourceProduct.AutoID;
newProduct.isFromFeed = true;
newProduct.isDeleted = false;
newProduct.SKU = sourceProduct.StockNumber;
company.Product.Add(newProduct);
}
}
_dbRiv.SaveChanges(); // ### THIS BREAKS ### //
}
}
}
break;
}
}
}
Model #1 - This model sits in a database on our Dev Server.
Model #1 http://content.screencast.com/users/Keith.Barrows/folders/Jing/media/bdb2b000-6e60-4af0-a7a1-2bb6b05d8bc1/Model1.png
Model #2 - This model sits in a database on our Prod Server and is updated each day by automatic feeds. alt text http://content.screencast.com/users/Keith.Barrows/folders/Jing/media/4260259f-bce6-43d5-9d2a-017bd9a980d4/Model2.png
Note - The red circled items in Model #1 are the fields I use to "map" to Model #2. Please ignore the red circles in Model #2: that is from another question I had which is now answered.
Note: I still need to put in an isDeleted check so I can soft delete it from DB1 if it has gone out of our client's inventory.
All I want to do, with this particular code, is connect a company in DB1 with a client in DB2, get their product list from DB2 and INSERT it in DB1 if it is not already there. First time through should be a full pull of inventory. Each time it is run there after nothing should happen unless new inventory came in on the feed over night.
So the big question - how to I solve the transaction error I am getting? Do I need to drop and recreate my context each time through the loops (does not make sense to me)?
After much pulling out of hair I discovered that the foreach loops were the culprits. What needs to happen is to call EF but return it into an IList<T> of that target type then loop on the IList<T>.
Example:
IList<Client> clientList = from a in _dbFeed.Client.Include("Auto") select a;
foreach (RivWorks.Model.NegotiationAutos.Client client in clientList)
{
var companyFeedDetailList = from a in _dbRiv.AutoNegotiationDetails where a.ClientID == client.ClientID select a;
// ...
}
As you've already identified, you cannot save from within a foreach that is still drawing from the database via an active reader.
Calling ToList() or ToArray() is fine for small data sets, but when you have thousands of rows, you will be consuming a large amount of memory.
It's better to load the rows in chunks.
public static class EntityFrameworkUtil
{
public static IEnumerable<T> QueryInChunksOf<T>(this IQueryable<T> queryable, int chunkSize)
{
return queryable.QueryChunksOfSize(chunkSize).SelectMany(chunk => chunk);
}
public static IEnumerable<T[]> QueryChunksOfSize<T>(this IQueryable<T> queryable, int chunkSize)
{
int chunkNumber = 0;
while (true)
{
var query = (chunkNumber == 0)
? queryable
: queryable.Skip(chunkNumber * chunkSize);
var chunk = query.Take(chunkSize).ToArray();
if (chunk.Length == 0)
yield break;
yield return chunk;
chunkNumber++;
}
}
}
Given the above extension methods, you can write your query like this:
foreach (var client in clientList.OrderBy(c => c.Id).QueryInChunksOf(100))
{
// do stuff
context.SaveChanges();
}
The queryable object you call this method on must be ordered. This is because Entity Framework only supports IQueryable<T>.Skip(int) on ordered queries, which makes sense when you consider that multiple queries for different ranges require the ordering to be stable. If the ordering isn't important to you, just order by primary key as that's likely to have a clustered index.
This version will query the database in batches of 100. Note that SaveChanges() is called for each entity.
If you want to improve your throughput dramatically, you should call SaveChanges() less frequently. Use code like this instead:
foreach (var chunk in clientList.OrderBy(c => c.Id).QueryChunksOfSize(100))
{
foreach (var client in chunk)
{
// do stuff
}
context.SaveChanges();
}
This results in 100 times fewer database update calls. Of course each of those calls takes longer to complete, but you still come out way ahead in the end. Your mileage may vary, but this was worlds faster for me.
And it gets around the exception you were seeing.
EDIT I revisited this question after running SQL Profiler and updated a few things to improve performance. For anyone who is interested, here is some sample SQL that shows what is created by the DB.
The first loop doesn't need to skip anything, so is simpler.
SELECT TOP (100) -- the chunk size
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name],
FROM [dbo].[Clients] AS [Extent1]
ORDER BY [Extent1].[Id] ASC
Subsequent calls need to skip previous chunks of results, so introduces usage of row_number:
SELECT TOP (100) -- the chunk size
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name],
FROM (
SELECT [Extent1].[Id] AS [Id], [Extent1].[Name] AS [Name], row_number()
OVER (ORDER BY [Extent1].[Id] ASC) AS [row_number]
FROM [dbo].[Clients] AS [Extent1]
) AS [Extent1]
WHERE [Extent1].[row_number] > 100 -- the number of rows to skip
ORDER BY [Extent1].[Id] ASC
We have now posted an official response to the bug opened on Connect. The workarounds we recommend are as follows:
This error is due to Entity Framework creating an implicit transaction during the SaveChanges() call. The best way to work around the error is to use a different pattern (i.e., not saving while in the midst of reading) or by explicitly declaring a transaction. Here are three possible solutions:
// 1: Save after iteration (recommended approach in most cases)
using (var context = new MyContext())
{
foreach (var person in context.People)
{
// Change to person
}
context.SaveChanges();
}
// 2: Declare an explicit transaction
using (var transaction = new TransactionScope())
{
using (var context = new MyContext())
{
foreach (var person in context.People)
{
// Change to person
context.SaveChanges();
}
}
transaction.Complete();
}
// 3: Read rows ahead (Dangerous!)
using (var context = new MyContext())
{
var people = context.People.ToList(); // Note that this forces the database
// to evaluate the query immediately
// and could be very bad for large tables.
foreach (var person in people)
{
// Change to person
context.SaveChanges();
}
}
Indeed you cannot save changes inside a foreach loop in C# using Entity Framework.
context.SaveChanges() method acts like a commit on a regular database system (RDMS).
Just make all changes (which Entity Framework will cache) and then save all of them at once calling SaveChanges() after the loop (outside of it), like a database commit command.
This works if you can save all changes at once.
Just put context.SaveChanges() after end of your foreach(loop).
Making your queryable lists to .ToList() and it should work fine.
FYI: from a book and some lines adjusted because it's still valid:
Invoking SaveChanges() method begins a transaction which automatically rolls back all changes persisted to the database if an exception occurs before iteration completes; otherwise the transaction commits. You might be tempted to apply the method after each entity update or deletion rather than after iteration completes, especially when you're updating or deleting massive numbers of entities.
If you try to invoke SaveChanges() before all data has been processed, you incur a "New transaction is not allowed because there are other threads running in the session" exception. The exception occurs because SQL Server doesn't permit starting a new transaction on a connection that has a SqlDataReader open, even with Multiple Active Record Sets (MARS) enabled by the connection string (EF's default connection string enables MARS)
Sometimes its better to understand why things are happening ;-)
Always Use your selection as List
Eg:
var tempGroupOfFiles = Entities.Submited_Files.Where(r => r.FileStatusID == 10 && r.EventID == EventId).ToList();
Then Loop through the Collection while save changes
foreach (var item in tempGroupOfFiles)
{
var itemToUpdate = item;
if (itemToUpdate != null)
{
itemToUpdate.FileStatusID = 8;
itemToUpdate.LastModifiedDate = DateTime.Now;
}
Entities.SaveChanges();
}
I was getting this same issue but in a different situation. I had a list of items in a list box. The user can click an item and select delete but I am using a stored proc to delete the item because there is a lot of logic involved in deleting the item. When I call the stored proc the delete works fine but any future call to SaveChanges will cause the error. My solution was to call the stored proc outside of EF and this worked fine. For some reason when I call the stored proc using the EF way of doing things it leaves something open.
We started seeing this error "New transaction is not allowed because there are other threads running in the session" after migrating from EF5 to EF6.
Google brought us here but we are not calling SaveChanges() inside the loop. The errors were raised when executing a stored procedure using the ObjectContext.ExecuteFunction inside a foreach loop reading from the DB.
Any call to ObjectContext.ExecuteFunction wraps the function in a transaction. Beginning a transaction while there is already an open reader causes the error.
It is possible to disable wrapping the SP in a transaction by setting the following option.
_context.Configuration.EnsureTransactionsForFunctionsAndCommands = false;
The EnsureTransactionsForFunctionsAndCommands option allows the SP to run without creating its own transaction and the error is no longer raised.
DbContextConfiguration.EnsureTransactionsForFunctionsAndCommands Property
Here are another 2 options that allow you to invoke SaveChanges() in a for each loop.
The first option is use one DBContext to generate your list objects to iterate through, and then create a 2nd DBContext to call SaveChanges() on. Here is an example:
//Get your IQueryable list of objects from your main DBContext(db)
IQueryable<Object> objects = db.Object.Where(whatever where clause you desire);
//Create a new DBContext outside of the foreach loop
using (DBContext dbMod = new DBContext())
{
//Loop through the IQueryable
foreach (Object object in objects)
{
//Get the same object you are operating on in the foreach loop from the new DBContext(dbMod) using the objects id
Object objectMod = dbMod.Object.Find(object.id);
//Make whatever changes you need on objectMod
objectMod.RightNow = DateTime.Now;
//Invoke SaveChanges() on the dbMod context
dbMod.SaveChanges()
}
}
The 2nd option is to get a list of database objects from the DBContext, but to select only the id's. And then iterate through the list of id's (presumably an int) and get the object corresponding to each int, and invoke SaveChanges() that way. The idea behind this method is grabbing a large list of integers, is a lot more efficient then getting a large list of db objects and calling .ToList() on the entire object. Here is an example of this method:
//Get the list of objects you want from your DBContext, and select just the Id's and create a list
List<int> Ids = db.Object.Where(enter where clause here)Select(m => m.Id).ToList();
var objects = Ids.Select(id => db.Objects.Find(id));
foreach (var object in objects)
{
object.RightNow = DateTime.Now;
db.SaveChanges()
}
If you get this error due to foreach and you really need to save one entity first inside loop and use generated identity further in loop, as was in my case, the easiest solution is to use another DBContext to insert entity which will return Id and use this Id in outer context
For example
using (var context = new DatabaseContext())
{
...
using (var context1 = new DatabaseContext())
{
...
context1.SaveChanges();
}
//get id of inserted object from context1 and use is.
context.SaveChanges();
}
I was also facing same issue.
Here is the cause and solution.
http://blogs.msdn.com/b/cbiyikoglu/archive/2006/11/21/mars-transactions-and-sql-error-3997-3988-or-3983.aspx
Make sure before firing data manipulation commands like inserts, updates, you have closed all previous active SQL readers.
Most common error is functions that read data from db and return values.
For e.g functions like isRecordExist.
In this case we immediately return from the function if we found the record and forget to close the reader.
So in the project were I had this exact same issue the problem wasn't in the foreach or the .toList() it was actually in the AutoFac configuration we used.
This created some weird situations were the above error was thrown but also a bunch of other equivalent errors were thrown.
This was our fix:
Changed this:
container.RegisterType<DataContext>().As<DbContext>().InstancePerLifetimeScope();
container.RegisterType<DbFactory>().As<IDbFactory>().SingleInstance();
container.RegisterType<UnitOfWork>().As<IUnitOfWork>().InstancePerRequest();
To:
container.RegisterType<DataContext>().As<DbContext>().As<DbContext>();
container.RegisterType<DbFactory>().As<IDbFactory>().As<IDbFactory>().InstancePerLifetimeScope();
container.RegisterType<UnitOfWork>().As<IUnitOfWork>().As<IUnitOfWork>();//.InstancePerRequest();
I know it is an old question but i faced this error today.
and i found that, this error can be thrown when a database table trigger gets an error.
for your information, you can check your tables triggers too when you get this error.
I needed to read a huge ResultSet and update some records in the table.
I tried to use chunks as suggested in Drew Noakes's answer.
Unfortunately after 50000 records I've got OutofMemoryException.
The answer Entity framework large data set, out of memory exception explains, that
EF creates second copy of data which uses for change detection (so
that it can persist changes to the database). EF holds this second set
for the lifetime of the context and its this set thats running you out
of memory.
The recommendation is to re-create your context for each batch.
So I've retrieved Minimal and Maximum values of the primary key- the tables have primary keys as auto incremental integers.Then I retrieved from the database chunks of records by opening context for each chunk. After processing the chunk context closes and releases the memory. It insures that memory usage is not growing.
Below is a snippet from my code:
public void ProcessContextByChunks ()
{
var tableName = "MyTable";
var startTime = DateTime.Now;
int i = 0;
var minMaxIds = GetMinMaxIds();
for (int fromKeyID= minMaxIds.From; fromKeyID <= minMaxIds.To; fromKeyID = fromKeyID+_chunkSize)
{
try
{
using (var context = InitContext())
{
var chunk = GetMyTableQuery(context).Where(r => (r.KeyID >= fromKeyID) && (r.KeyID < fromKeyID+ _chunkSize));
try
{
foreach (var row in chunk)
{
foundCount = UpdateRowIfNeeded(++i, row);
}
context.SaveChanges();
}
catch (Exception exc)
{
LogChunkException(i, exc);
}
}
}
catch (Exception exc)
{
LogChunkException(i, exc);
}
}
LogSummaryLine(tableName, i, foundCount, startTime);
}
private FromToRange<int> GetminMaxIds()
{
var minMaxIds = new FromToRange<int>();
using (var context = InitContext())
{
var allRows = GetMyTableQuery(context);
minMaxIds.From = allRows.Min(n => (int?)n.KeyID ?? 0);
minMaxIds.To = allRows.Max(n => (int?)n.KeyID ?? 0);
}
return minMaxIds;
}
private IQueryable<MyTable> GetMyTableQuery(MyEFContext context)
{
return context.MyTable;
}
private MyEFContext InitContext()
{
var context = new MyEFContext();
context.Database.Connection.ConnectionString = _connectionString;
//context.Database.Log = SqlLog;
return context;
}
FromToRange is a simple structure with From and To properties.
Recently I faced the same issue in my project so posting my experience and it might help some on the same boat as i was. The issue was due to i am looping through the results of EF select query (results are not retrieved into memory).
var products = (from e in _context.Products
where e.StatusId == 1
select new { e.Name, e.Type });
foreach (var product in products)
{
//doing some insert EF Queries
//some EF select quries
await _context.SaveChangesAsync(stoppingToken); // This code breaks.
}
I have updated my Products select query to bring the results into LIST rather than IQueryable (This seems to be opening the reader throughout for each loop and hence save was failing).
var products = (from e in _context.Products
where e.StatusId == 1
select new { e.Name, e.Type })**.ToList()**; //see highlighted
The code below works for me:
private pricecheckEntities _context = new pricecheckEntities();
...
private void resetpcheckedtoFalse()
{
try
{
foreach (var product in _context.products)
{
product.pchecked = false;
_context.products.Attach(product);
_context.Entry(product).State = EntityState.Modified;
}
_context.SaveChanges();
}
catch (Exception extofException)
{
MessageBox.Show(extofException.ToString());
}
productsDataGrid.Items.Refresh();
}
In my case, the problem appeared when I called Stored Procedure via EF and then later SaveChanges throw this exception. The problem was in calling the procedure, the enumerator was not disposed. I fixed the code following way:
public bool IsUserInRole(string username, string roleName, DataContext context)
{
var result = context.aspnet_UsersInRoles_IsUserInRoleEF("/", username, roleName);
//using here solved the issue
using (var en = result.GetEnumerator())
{
if (!en.MoveNext())
throw new Exception("emty result of aspnet_UsersInRoles_IsUserInRoleEF");
int? resultData = en.Current;
return resultData == 1;//1 = success, see T-SQL for return codes
}
}
I am much late to the party but today I faced the same error and how I resolved was simple. My scenario was similar to this given code I was making DB transactions inside of nested for-each loops.
The problem is as a Single DB transaction takes a little bit time longer than for-each loop so once the earlier transaction is not complete then the new traction throws an exception, so the solution is to create a new object in the for-each loop where you are making a db transaction.
For the above mentioned scenarios the solution will be like this:
foreach (RivWorks.Model.Negotiation.AutoNegotiationDetails companyFeedDetail in companyFeedDetailList)
{
private RivWorks.Model.Negotiation.RIV_Entities _dbRiv = RivWorks.Model.Stores.RivEntities(AppSettings.RivWorkEntities_connString);
if (companyFeedDetail.FeedSourceTable.ToUpper() == "AUTO")
{
var company = (from a in _dbRiv.Company.Include("Product") where a.CompanyId == companyFeedDetail.CompanyId select a).First();
foreach (RivWorks.Model.NegotiationAutos.Auto sourceProduct in client.Auto)
{
foreach (RivWorks.Model.Negotiation.Product targetProduct in company.Product)
{
if (targetProduct.alternateProductID == sourceProduct.AutoID)
{
found = true;
break;
}
}
if (!found)
{
var newProduct = new RivWorks.Model.Negotiation.Product();
newProduct.alternateProductID = sourceProduct.AutoID;
newProduct.isFromFeed = true;
newProduct.isDeleted = false;
newProduct.SKU = sourceProduct.StockNumber;
company.Product.Add(newProduct);
}
}
_dbRiv.SaveChanges(); // ### THIS BREAKS ### //
}
}
I am a little bit late, but I had this error too. I solved the problem by checking what where the values that where updating.
I found out that my query was wrong and that there where over 250+ edits pending. So I corrected my query, and now it works correct.
So in my situation: Check the query for errors, by debugging over the result that the query returns. After that correct the query.
Hope this helps resolving future problems.
My situation was similar others above. I had an IQueryable which I was doing a foreach on. This in turn called a method with SaveChanges(). Booom exception here as there was already a transaction open from the query above.
// Example:
var myList = _context.Table.Where(x => x.time == null);
foreach(var i in myList)
{
MyFunction(i); // <<-- Has _context.SaveChanges() which throws exception
}
Adding ToList() to the end of the query was the solution in my case.
// Fix
var myList = _context.Table.Where(x => x.time == null).ToList();
Most of answers related with loops. But my problem was different. While i was trying to use multiple dbcontext.Savechanges() command in same scope, i got the error many times.
In my case for ef core 3.1 using
dbcontext.Database.BeginTransaction()
and
dbcontext.Database.CommitTransaction();
has fixed the problem. Here is my entire Code :
public IActionResult ApplyForCourse()
{
var master = _userService.GetMasterFromCurrentUser();
var trainee = new Trainee
{
CourseId = courseId,
JobStatus = model.JobStatus,
Gender = model.Gender,
Name = model.Name,
Surname = model.Surname,
Telephone = model.Telephone,
Email = model.Email,
BirthDate = model.BirthDate,
Description = model.Description,
EducationStatus = EducationStatus.AppliedForEducation,
TraineeType = TraineeType.SiteFirst
};
dbcontext.Trainees.Add(trainee);
dbcontext.SaveChanges();
dbcontext.Database.BeginTransaction();
var user = userManager.GetUserAsync(User).Result;
master.TraineeId = trainee.Id;
master.DateOfBirth = model.BirthDate;
master.EducationStatus = trainee.EducationStatus;
user.Gender = model.Gender;
user.Email = model.Email;
dbcontext.Database.CommitTransaction();
dbcontext.SaveChanges();
return RedirectToAction("Index", "Home");
}
}
Well, I have this code:
var companyId = 1;
var categoryId = 1;
var item = _dbContext.FirstOrDefault(i =>
i.CompanyId == companyId && i.CategoryId == categoryId);
if (item == null) {
var newItem = new Item()
{
CategoryId = companyId,
CompanyId = categoryId,
// some other properties
};
_dbContext.Items.Add(newItem);
_dbContext.SaveChanges();
}
else
{
// update some properties of the item (not CompanyId or CategoryId)
item.xyz = "new Value"
_dbContext.Items.Update(item);
_dbContext.SaveChanges();
}
This is the only piece of code where I access Items table. I want to make sure no duplicate entries are made for CompanyId-CategoryId combination, that is to say, this combination should be unique. But even though the code checks for the existence before insertion, how do I end up having duplicate entries in the database?
Please ignore everything else (the architecture, the use of DB Context etc since I have just written this simple code to understand the problem). Also, I know I can implement this thing at DB level and make columns combination unique, but is there any way to do this in application code (in C#)? I am using EF, if that's important. Why exactly is this problem caused, multithreading?
Please help me understand this issue or give me some directions to what further I should read in this regard. Thanks.
If you want to do this in application code, then you are going to have to force single threading somewhere. One way to do this would be to use locking to produce a section of code that only one thread can enter at a time. You then would re-check existence of the record and if still null perform your insert. It would look something like this:
// declared at class level
private static readonly object ItemCreationSyncLock = new object();
public void MyMethodThatCreatesAnItem()
{
// ... setup code ...
var item = _dbContext.Items.FirstOrDefault(itm => item.Name == criteria);
if(item == null)
{
lock(ItemCreationSyncLock)
{
item = _dbContext.Items.FirstOfDefault(itm => item.Name == criteria);
if(item == null)
{
item = new Item { Name = criteria };
_dbContext.Items.Add(item);
_dbContext.SaveChanges();
}
}
}
}
So I covered the "how" of avoiding the duplicate entry in the application code, but it is important to realize that even as a backup to this you would still want to enforce a unique constraint at the database level if you really want to ensure duplicates cannot exist. I am capable of defeating the guard that I just showed you by scaling the application out to multiple instances, whether using web garden/farm or scaling to additional instances on Azure.
Using a lock in C# will only work if you have a single web server. If you have a farm, then each instance of your application will have its own ItemCreationSyncLock.
To create a synchronization lock in the database, for SQL Server is as simple as this:
using (var db = new Db())
using (var tran = db.Database.BeginTransaction())
{
db.Database.ExecuteSqlCommand("exec sp_getapplock 'MyAppLock','exclusive';");
//only one thread across all application instances will execute this code at one time
tran.Commit();
}
I think that's a common problem but I haven't found any solution, perhaps I'm not searching for the problem correctly in google. In summary, I have a process that inserts multiple rows in a table (among a lot of other things in the same transaction), but the process is executed in multiple threads and multiple servers.
TABLE: COVERAGES
COLUMNS: COV_Id, COV_Description
The description is Unique, but not as a constraint in database (legacy), and I want to avoid to insert duplicate descriptions. I've isolated the search and insert in a independent transaction and I want to lock the table before select and liberate it after "Save" if it not exists.
I would something like that (high level):
{
this.Lock(Coverage); // Lock table Coverages to avoid select out of this transaction
Coverage coverage = session.QueryOver<Coverage>().Where(g => g.Description == description).Take(1).SingleOrDefault();
if (coverage == null)
{
this.Save(new Coverage { Description = description });
}
return coverage;
};
I can't use lock instruction of C# because the process is executed in multiple servers, and I can't use Lock instruction of NHibernate, because precisely I want to block when I've no results.
I'm using NHibernate 3.3 for SqlServer and Oracle.
I finally implement a semaphore on database to solve the problem. As I mention on my above "discussion" with Frédéric, I need to lock the thread at select to avoid duplicate insertion, the Serializable isolation level, locks on INSERT and throws deadlock exceptions when the insert is called in concurrent calls on SQL Server. By other way on Oracle throws error 08177. 00000 - "can't serialize access for this transaction", or keeps waiting for the end of the other transaction inserting the value duplicated later (see sample sql's below).
So the solution is something like this:
public Coverage CreateCoverageSessionIsolated(string description, out bool isNew)
{
Coverage coverage = null;
bool _isNew = false;
this.ExecuteOnNewSession((session) =>
{
this.semphoresDao.LockSemaphore(session, "SMF_COVERAGES");
coverage = session.QueryOver<Coverage>()
.Where(g => g.Description == description)
.Take(1)
.SingleOrDefault();
_isNew = coverage == null;
if (coverage == null)
{
coverage = new Coverage { Description = description };
this.Save(coverage);
}
});
isNew = _isNew;
return coverage;
}
I adapt the real code a bit to better comprension.
ExecuteOnNewSession, starts a new isolated ReadCommitted transaction. So it doesn't interferes with opened transaction, to avoid timeouts on uncontrolled locks and deadlocks and reduces the risk time.
LockSempahore: Executes a select query, locking specific row.
I've tried it and works fine on SQL Server and Oracle.
EDIT:
To check that the solution of Serializable transaction doesn't fit for me I use that simple SQL code on two concurrent transactions executing step by step, side by side:
BEGIN TRAN; -- ONLY FOR SQL
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
SELECT COV_ID FROM COVERAGES WHERE COV_DESCRIPTION = 'testcov';
INSERT INTO COVERAGES (COV_DESCRIPTION) VALUES ('testcov');
COMMIT;
You may lock your table with a transaction using IsolationLevel.Serializable.
using (var t = session.BeginTransaction(IsolationLevel.Serializable))
{
var coverage = session.QueryOver<Coverage>()
.Where(g => g.Description == description)
.Take(1).SingleOrDefault();
if (coverage == null)
{
coverage = new Coverage { Description = description };
session.Save(coverage);
}
t.Commit();
return coverage;
}
For limiting lock contention, this requires that your table has an index on Description and that this index is actually used by the reading query. Otherwise, it will lock the entire table instead of just locking "nearby" Description values. Read more here. For official documentation a bit more complete than .Net Framework one, read here and here.
In case two or more processes (or threads) attempt to perform concurrent conflicting inserts1, they will all encounter a deadlock. All of them excepted one will be rollbacked as deadlocks victims. The remaining single one will carry on.
The deadlock occurs on the insert, not on the select. All the processes will hang on the insert, all ending rollbacked, excepted one. This ensures no duplicates will be inserted.
This means the complete code for handling that is a bit more elaborated.
while (true)
{
using (var session = sessFactory.OpenSession())
{
try
{
using (var t = session.BeginTransaction(IsolationLevel.Serializable))
{
var coverage = session.QueryOver<Coverage>()
.Where(g => g.Description == description)
.Take(1).SingleOrDefault();
if (coverage == null)
{
coverage = new Coverage { Description = description };
session.Save(coverage);
}
t.Commit();
// Breaks the loop by the way.
return coverage;
}
}
catch (GenericADOException ex)
{
// SQL-Server specific code for identifying deadlocks
var sqlEx = ex.InnerException as SqlException;
if (sqlEx == null || sqlEx.Number != 1205)
throw;
// Deadlock, just try again by letting the loop go on (eventually
// log it).
}
}
}
Note:
1. Conflicting according to the range locked by the DB, not only about the actual value to insert. Having an adequate index is highly recommended for reducing this range. Not having one may cause the whole table to be locked, resulting in a very poor ability to concurrently insert different values.
I have delete an application in c# and i utilize linq to entities to build queries in my application. However I find my application to be very slow in adding and deleting records. Delete 500 records would take me about 15 mins. That is too long. my delete query is below.
public void deletePayrollBatch(int batchNo)
{
var context = new DataSources.sspEntities();
var query1 = (from a in context.Payroll_Details
where a.Payroll_BatchBatch_no == batchNo
select a).ToList();
foreach (var x in query1)
{
context.DeleteObject(x);
context.SaveChanges();
}
}
My query is rather simple. One row of data does contain about 20 columns. I dont know if that would have an effect. Anyhow, if i can get some expert suggestion, it would be helpful. thank you.
EDITED.
I already had good suggestions based on the delete. One of which is to used context.SaveChanges() outside of the loop. In my insert, i have similar code (shown below), however I need the record to be save first because i want the ID to use it in another function. In this case, how may i proceed?
foreach (var xyz in x)
{
Try{
pDetails1.EstateID = 143;
pDetails1.Employee_Personal_InfoEmp_id = xyz.PD_EmpPersonal_Id;
pDetails1.PAYE = (decimal)xyz.PD_PAYE.GetValueOrDefault();
pDetails1.PAYE_YTD = (decimal)PayeYTD.GetValueOrDefault();
pDetails1.Basic_Pay = (decimal)xyz.PD_BasicPay.GetValueOrDefault();
pDetails1.Basic_Pay_YTD = (decimal)basicpay_YTD.GetValueOrDefault();
pDetails1.Gross_Pay = (decimal)xyz.PD_GrossPay.GetValueOrDefault();
pDetails1.Gross_Pay_YTD = (decimal)GrossPay_YTD.GetValueOrDefault();
context.SaveChanges();
Functions.RandomFunct rf = new RandomFunct();
rf.AdditionalEarningsIsContinuous(xyz.PD_EmpPersonal_Id); // I NEED THE ID IN ORDER TO RUN THIS FUNCTION. IN THIS CASE I HAVE TO SAVE ON EACH ELEMENT IN THE FOR EACH LOOP??
}
catch (exeception e)
debug.writeline(e.message);
}
You are calling context.SaveChanges for every record. You can do that once at the end of your foreach loop.
foreach (var x in query1)
{
context.DeleteObject(x);
}
context.SaveChanges();
That will send the request to delete once to the database for all records. Currently you are sending DELETE request for each record and that is taking time.
I'm trying to add a bulk of data in my DbContext (SQLite DB).
What I want is to add x amount of data, and if some of them already exist, ignore those. So for example: add 100, 2 already exist, 98 items are added.
First I did a insert of all of them and then call saveChanges(), but that reverted the insert of all of them. Therefore I changed it to saveChanges() in the for-loop but I'm experiencing the same problem.
Do I need to clear something after an exception?
public int Insert(List<Car> Cars)
{
int addedCars = 0;
foreach (Car t in Cars)
{
_db.Cars.Add(t);
try
{
_db.SaveChanges();
addedCars++;
}
catch (DbUpdateException ex)
{
Console.WriteLine("Whups duplicate entry");
}
}
return addedCars;
}
You would need to remove it from the context. You're receiving an exception, but the entity is still "added" to the context. So the next time you SaveChanges(), you'll get the same exception.
Option 1:
public int Insert(List<Car> Cars)
{
int addedCars = 0;
foreach (Car t in Cars)
{
_db.Cars.Add(t);
try
{
_db.SaveChanges();
addedCars++;
}
catch (DbUpdateException ex)
{
_db.cars.Remove(t); // Remove it from the context collection
Console.WriteLine("Whups duplicate entry");
}
}
return addedCars;
}
Option 2 (preferred):
I really suggest you not even attempt to add the entities if they already exist.
You could do this before your add logic:
Cars = Cars.Where(x => !_db.Cars.Any(y => y.ID == x.ID)).ToList();
Note that even though this technically "checks" 100 records, it is doing so in memory with a single SQL statement. This is much faster than inserting even a few records erroneously.
Can't you just test if the item already exists before adding it?
if(!_db.Cars.Any(c => c == t))
{
_db.Cars.Add(t);
}