See Resolving optimistic concurrency exceptions with Reload (database wins) :
using (var context = new BloggingContext())
{
var blog = context.Blogs.Find(1);
blog.Name = "The New ADO.NET Blog";
bool saveFailed;
do
{
saveFailed = false;
try
{
context.SaveChanges();
}
catch (DbUpdateConcurrencyException ex)
{
saveFailed = true;
// Update the values of the entity that failed to save from the store
ex.Entries.Single().Reload();
}
} while (saveFailed);
}
Why the method SaveChanges() is called after Reload()?
This call will never change the data in the database.
I agree it's not too clear. The intention of this piece of code is in the sentence
The entity is then typically given back to the user in some form and they must try to make their changes again and re-save.
So it would have been better if they had added a comment:
...
// User evaluates current values and may make new changes.
try
{
context.SaveChanges();
}
...
Related
I am building an API where I get a specific object sent as a JSON and then it gets converted into another object of another type, so we have sentObject and convertedObject. Now I can do this:
using (var dbContext = _dbContextFactory.CreateDbContext())
using (var dbContext2 = _dbContextFactory2.CreateDbContext())
{
await dbContext.AddAsync(sentObject);
await dbContext.SaveChangesAsync();
await dbContext2.AddAsync(convertedObject);
await dbContext2.SaveChangesAsync();
}
Now I had a problem where the first SaveChanges call went ok but the second threw an error with a datefield that was not properly set. The first SaveChanges call happened so the data is inserted in the database while the second SaveChanges failed, which cannot happen in my use-case.
What I want to do is if the second SaveChanges call goes wrong then I basically want to rollback the changes that have been made by the first SaveChanges.
My first thought was to delete cascade but the sentObject has a complex structure and I don't want to run into circular problems with delete cascade.
Is there any tips on how I could somehow rollback my changes if one of the SaveChanges calls fails?
You can call context.Database.BeginTransaction as follows:
using (var dbContextTransaction = context.Database.BeginTransaction())
{
context.Database.ExecuteSqlCommand(
#"UPDATE Blogs SET Rating = 5" +
" WHERE Name LIKE '%Entity Framework%'"
);
var query = context.Posts.Where(p => p.Blog.Rating >= 5);
foreach (var post in query)
{
post.Title += "[Cool Blog]";
}
context.SaveChanges();
dbContextTransaction.Commit();
}
(taken from the docs)
You can therefore begin a transaction for dbContext in your case and if the second command failed, call dbContextTransaction.Rollback();
Alternatively, you can implement the cleanup logic yourself, but it would be messy to maintain that as your code here evolves in the future.
Here is an example code that is working for me, no need for calling the rollback function. Calling the rollback function can fail. If you do it inside the catch block for example then you have a silent exception that gets thrown and you will never know about it. The rollback happens automatically when the transaction object in the using statement gets disposed. You can see this if you go to SSMS and look for the open transactions while debugging. See this for reference: https://github.com/dotnet/EntityFramework.Docs/issues/327
Using Transactions or SaveChanges(false) and AcceptAllChanges()?
using (var transactionApplication = dbContext.Database.BeginTransaction())
{
try
{
await dbContext.AddAsync(toInsertApplication);
await dbContext.SaveChangesAsync();
using (var transactionPROWIN = dbContextPROWIN.Database.BeginTransaction())
{
try
{
await dbContext2.AddAsync(convertedApplication);
await dbContext2.SaveChangesAsync();
transaction2.Commit();
insertOperationResult = ("Insert successfull", false);
}
catch (Exception e)
{
Logger.LogError(e.ToString());
insertOperationResult = ("Insert converted object failed", true);
return;
}
}
transactionApplication.Commit();
}
catch (DbUpdateException dbUpdateEx)
{
Logger.LogError(dbUpdateEx.ToString());
if (dbUpdateEx.InnerException.ToString().ToLower().Contains("overflow"))
{
insertOperationResult = ("DateTime overflow", true);
return;
}
//transactionApplication.Rollback();
insertOperationResult = ("Duplicated UUID", true);
}
catch (Exception e)
{
Logger.LogError(e.ToString());
transactionApplication.Rollback();
insertOperationResult = ("Insert Application: Some other error happened", true);
}
}
UPDATED: I have a piece of code that creates records when they don't exist, or updates them when they do exist. However, while trying to update the records I get this exception:
Microsoft.EntityFrameworkCore.DbUpdateException The DELETE statement
conflicted with the REFERENCE constraint
public static string AddCurrencies(ApplicationDbContext db)
{
// ...
foreach (Currency c in db.Currency.ToList())
{
try
{
db.Remove(c); // the troublemaker!
db.SaveChanges();
}
catch
{
// probably in use (foreign key)
}
}
// ...
foreach (Currency c in CurrencyList)
{
var c_db = db.Currency.FirstOrDefault(x => x.Code == c.Code);
if (c_db == null)
{
// adding
db.Currency.Add(c);
}
else
{
// updating
c_db.Name = c.Name;
c_db.LocalDisplay = c.LocalDisplay;
}
db.SaveChanges(); // exception fired if updating!
}
// ...
}
After some investigation, and having being able to turn SQL debugging on, I found out that the Remove() "persists" and that it will be retried with the second call to SaveChanges(), hence the exception. Now the question is reformulated: how do I "undo" (in the lack of a better expression) the Remove() commands that failed?
I managed to solve this issue this way:
var entry = context.Entry(entity);
entry.Reload();
for each entry where delete failed.
I am using EntityFramework Core commands to migration database. The command I am using is like the docs suggests: dnx . ef migration apply. The problem is when specifying AttachDbFileName in connection string, the following error appear: Unable to Attach database file as database xxxxxxx. This is the connection string I am using:
Data Source=(LocalDB)\mssqllocaldb;Integrated Security=True;Initial Catalog=EfGetStarted2;AttachDbFileName=D:\EfGetStarted2.mdf
Please help how to attach the db file to another location.
Thanks
EF core seem to have troubles with AttachDbFileName or doesn't handle it at all.
EnsureDeleted changes the database name to master but keeps any AttachDbFileName value, which leads to an error since we cannot attach the master database to another file.
EnsureCreated opens a connection using the provided AttachDbFileName value, which leads to an error since the file of the database we want to create does not yet exist.
EF6 has some logic to handle these use cases, see SqlProviderServices.DbCreateDatabase, so everything worked quite fine.
As a workaround I wrote some hacky code to handle these scenarios:
public static void EnsureDatabase(this DbContext context, bool reset = false)
{
if (context == null)
throw new ArgumentNullException(nameof(context));
if (reset)
{
try
{
context.Database.EnsureDeleted();
}
catch (SqlException ex) when (ex.Number == 1801)
{
// HACK: EF doesn't interpret error 1801 as already existing database
ExecuteStatement(context, BuildDropStatement);
}
catch (SqlException ex) when (ex.Number == 1832)
{
// nothing to do here (see below)
}
}
try
{
context.Database.EnsureCreated();
}
catch (SqlException ex) when (ex.Number == 1832)
{
// HACK: EF doesn't interpret error 1832 as non existing database
ExecuteStatement(context, BuildCreateStatement);
// this takes some time (?)
WaitDatabaseCreated(context);
// re-ensure create for tables and stuff
context.Database.EnsureCreated();
}
}
private static void WaitDatabaseCreated(DbContext context)
{
var timeout = DateTime.UtcNow + TimeSpan.FromMinutes(1);
while (true)
{
try
{
context.Database.OpenConnection();
context.Database.CloseConnection();
}
catch (SqlException)
{
if (DateTime.UtcNow > timeout)
throw;
continue;
}
break;
}
}
private static void ExecuteStatement(DbContext context, Func<SqlConnectionStringBuilder, string> statement)
{
var builder = new SqlConnectionStringBuilder(context.Database.GetDbConnection().ConnectionString);
using (var connection = new SqlConnection($"Data Source={builder.DataSource}"))
{
connection.Open();
using (var command = connection.CreateCommand())
{
command.CommandText = statement(builder);
command.ExecuteNonQuery();
}
}
}
private static string BuildDropStatement(SqlConnectionStringBuilder builder)
{
var database = builder.InitialCatalog;
return $"drop database [{database}]";
}
private static string BuildCreateStatement(SqlConnectionStringBuilder builder)
{
var database = builder.InitialCatalog;
var datafile = builder.AttachDBFilename;
var dataname = Path.GetFileNameWithoutExtension(datafile);
var logfile = Path.ChangeExtension(datafile, ".ldf");
var logname = dataname + "_log";
return $"create database [{database}] on primary (name = '{dataname}', filename = '{datafile}') log on (name = '{logname}', filename = '{logfile}')";
}
It's far from nice, but I'm using it for integration testing anyway. For "real world" scenarios using EF migrations should be the way to go, but maybe the root cause of this issue is the same...
Update
The next version will include support for AttachDBFilename.
There may be a different *.mdf file already attached to a database named EfGetStarted2... Try dropping/detaching that database then try again.
You might also be running into problems if the user LocalDB is running as doesn't have correct permissions to the path.
I get a runtime exception from the below code. I think it is not creating a primary key (which is CustomerID, and int). I used the Wizard and I have experience from years ago with ADO.NET but this is my first project using Entity Framework 6.0 with DbContext. I generated the EDMX file using "database first", so an actual database is present. I don't think any other table has a foreign key association with this table that is mandatory, so I think (but am not sure) this runtime error is from a failure to create new primary key. This is either a very easy question or a hard one, so I will check later.
Paul
[OperationContract]
public void DoWork ()
{
try
{
using (var ctx = new MyEDMXdBExistingDatabase())
{
CUSTOMER myCustomerREALLYNEW = new CUSTOMER();
myCustomerREALLYNEW.LastName = "NeWLASTNAME";
myCustomerREALLYNEW.CustomerID = 0; //set primary key to zero and let entity framework create new one automagically? I think this works based on past experience, but it's not working now
ctx.CUSTOMERs.Add(myCustomerREALLYNEW);
ctx.SaveChanges(); //PROBLEM HERE If comment out this line no runtime error
}
}
catch (DbEntityValidationException ex1)
{
Debug.WriteLine(ex1.Message);
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
}
finally
{
}
}
I added the following code and it showed me that the new CUSTOMER was lacking a manditory, non-null field (the Address). Once I added myCustomerREALLYNEW.Address= "123 Street"; then the new record/object could be added.
Here is the code I added to catch the runtime exception, which I got off the net:
catch (DbEntityValidationException ex1)
{
Debug.WriteLine("!" + ex1.Message);
List<string> errorMessages = new List<string>();
foreach (DbEntityValidationResult validationResult in ex1.EntityValidationErrors)
{
string entityName = validationResult.Entry.Entity.GetType().Name;
foreach (DbValidationError error in validationResult.ValidationErrors)
{
errorMessages.Add(entityName + "." + error.PropertyName + ":" + errorMessages);
}
}
foreach (string s in errorMessages)
{
Debug.WriteLine(s);
}
}
I am trying to solve situation with rolling back our datacontexts.
We are using one TransactionScope and inside two data contexts of two different databases.
At the end we want to save changes on both databases so we call .SaveChanges but the problem is that when an error occurs on the other database the changes on the first database are still saved.
What am I doing wrong in there that the first database doesn't roll back?
Thank you,
Jakub
public void DoWork()
{
using (var scope = new TransactionScope())
{
using (var rawData = new IntranetRawDataDevEntities())
{
rawData.Configuration.AutoDetectChangesEnabled = true;
using (var dataWareHouse = new IntranetDataWareHouseDevEntities())
{
dataWareHouse.Configuration.AutoDetectChangesEnabled = true;
... some operations with the data - no savechanges() is being called.
// Save changes for all items.
if (!errors)
{
// First database save.
rawData.SaveChanges();
// Fake data to fail the second database save.
dataWareHouse.Tasks.Add(new PLKPIDashboards.DataWareHouse.Task()
{
Description = string.Empty,
Id = 0,
OperationsQueue = new OperationsQueue(),
Queue_key = 79,
TaskTypeSLAs = new Collection<TaskTypeSLA>(),
Tasktype = null
});
// Second database save.
dataWareHouse.SaveChanges();
scope.Complete();
}
else
{
scope.Dispose();
}
}
}
}
From this article http://blogs.msdn.com/b/alexj/archive/2009/01/11/savechanges-false.aspx
try to use
rawData.SaveChanges(false);
dataWareHouse.SaveChanges(false);
//if everything is ok
scope.Complete();
rawData.AcceptAllChanges();
dataWareHouse.AcceptAllChanges();