EF does not detect concurrency update fail since FBClient returns row filled
with null (storage generated) values instead of "nothing" (empty result)
-----------------------------------------------------------------------------------------------------------------------------------------------------
Key: DNET-738
URL: http://tracker.firebirdsql.org/browse/DNET-738
Project: .NET Data provider
Issue Type: Bug
Components: ADO.NET Provider
Affects Versions: 5.1.1.0
Environment: FirebirdServer 2.5.4, .NET 4.5.1, EF 6.1.3
Reporter: Jiri Fartak
Assignee: Jiri Cincura
Synopsis:
FirebirdClient uses Execute block statements wrapping UPDATE command clause
having RETURNING statement to return server-generated values (e.g. identity
column, version...etc) back to EF.
This is typical example of such command:
-----
EXECUTE BLOCK (
p0 TIMESTAMP = @p0, p1 VARCHAR(16) CHARACTER SET UTF8 = @p1, p2 BIGINT = @p2,
p3 CHAR(16) CHARACTER SET OCTETS = @p3, p4 BIGINT = @p4, p5 INT = @p5
) RETURNS (
"created" TIMESTAMP, "creator" VARCHAR(16), "deleted" TIMESTAMP, "deletor"
VARCHAR(16), "version" INT)
AS BEGIN
UPDATE "PersistentObject"
SET "createdByOid" = NULL, "modified" = :p0, "modifier" = :p1, "modifiedByOid"
= :p2, "deletedByOid" = NULL, "clsid" = :p3
WHERE (("oid" = :p4) AND ("version" = :p5))
RETURNING "created", "creator", "deleted", "deletor", "version" INTO
:"created", :"creator", :"deleted", :"deletor", :"version";
SUSPEND;
END
------
The problem arises when UPDATE fails - when no row is updated due to
concurrency, since no rows satisfied WHERE constraints (version has changed).
If so, the following SUSPEND directive returns the row having ALL columns
filled with null values to the caller.
This is misleading to EF (control layer), beacuse the presence of the row
(albait with null values) causes, that command issued by EF will read this row
(via FBDataReader()) as valid row (and so rowsAffected is 1 and not zero) and
EF will then try to update entity's properties with these server-ganerated
values (calls translator.BackPropagateServerGen()). However, since the row is
having only null values, then properties that require value (.Required()) will
make the EF to throw exception due to inconsistency (see below).
This is excerpt of control in
System\Data\Mapping\Update\Internal\UpdateTranslator.cs:
foreach (UpdateCommand command in orderedCommands)
{
// Remember the data sources so that we can throw
meaningful exception
source = command;
!!!! rowsAffected will have value of 1 instead of 0, since
command.Execute returned row with nulls and not empty result set
long rowsAffected = command.Execute(translator, connection,
identifierValues, generatedValues);
!!! The line below would throw DbConcurrencyException (as we
want and expect) if rowsAffected would be zero, this does not happen
translator.ValidateRowsAffected(rowsAffected, source);
}
!! Following method throws the exception informing about inconsistency in
server generated value and requirements for property in model
translator.BackPropagateServerGen(generatedValues);
The FBClient behavior makes EF to throw this exception - informing about
inconsistency - even though the problem was caused by concurrency update:
A null store-generated value was returned for a non-nullable member 'Created'
of type 'WMS.Altair.Service.Repository.PersistentObjectModel'.
A null store-generated value was returned for a non-nullable member 'Created'
of type 'WMS.Altair.Service.Repository.PersistentObjectModel'.
Výpis: Vnitřní výpis chyby:--->Typ chyby: DbUpdateExceptionZpráva: A null
store-generated value was returned for a non-nullable member 'Created' of
type'WMS.Altair.Service.Repository.PersistentObjectModel'.Výpis: v
WMS.Altair.Service.Repository.IPAddressManager.Update(IPAddressModel model) v
WMS.Altair.Web.Controllers.IPAddressController.Edit(IPAddressEditViewModel
viewModel, StoreObjectState objectStates)Vnitřní výpis chyby:--->Typ chyby:
UpdateExceptionZpráva: A null store-generated value was returned for a
non-nullable member 'Created' of type
'WMS.Altair.Service.Repository.PersistentObjectModel'.Výpis: v
System.Data.Entity.Core.Mapping.Update.Internal.PropagatorResult.AlignReturnValue(Object
value, EdmMember member) v
System.Data.Entity.Core.Mapping.Update.Internal.PropagatorResult.SetServerGenValue(Object
value) v
System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.BackPropagateServerGen(List`1
generatedValues) v
System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.Update() v
System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.b__2(UpdateTranslator
ut) v System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.Update[T](T
noChangesResult, Func`2 updateFunction) v
System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.Update() v
System.Data.Entity.Core.Objects.ObjectContext.b__35() v
System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1
func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction,
Boolean releaseConnectionOnSuccess) v
System.Data.Entity.Core.Objects.ObjectContext.SaveChangesToStore(SaveOptions
options, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction)
v System.Data.Entity.Core.Objects.ObjectContext.<>c__DisplayClass2a.b__27() v
System.Data.Entity.Infrastructure.DefaultExecutionStrategy.Execute[TResult](Func`1
operation) v
System.Data.Entity.Core.Objects.ObjectContext.SaveChangesInternal(SaveOptions
options, Boolean executeInExistingTransaction) v
System.Data.Entity.Core.Objects.ObjectContext.SaveChanges(SaveOptions options)
v System.Data.Entity.Internal.InternalContext.SaveChanges()
However, this exception would be throwed when FBClient would return empty
result to EF:
--->
Typ chyby: DbUpdateConcurrencyException
Zpráva: Store update, insert, or delete statement affected an unexpected number
of rows (0). Entities may have been modified or deleted since entities were
loaded. See http://go.microsoft.com/fwlink/?LinkId=472540 for information on
understanding and handling optimistic concurrency exceptions.
Výpis: v WMS.Altair.Service.Repository.IPAddressManager.Update(IPAddressModel
model) v C:\Users\genx.INTRANET\Documents\Visual Studio
2013\Projects\AltairWebClient\AltairServices\Repository\UseCaseManager\IPAddressManager\IPAddressManager.cs:řádek
661 v
WMS.Altair.Web.Controllers.IPAddressController.Edit(IPAddressEditViewModel
viewModel, StoreObjectState objectStates) v
C:\Users\genx.INTRANET\Documents\Visual Studio
2013\Projects\AltairWebClient\AltairWebClient\Controllers\IPAddressController.cs:řádek
485
Vnitřní výpis chyby:
--->
Typ chyby: OptimisticConcurrencyException
Zpráva: Store update, insert, or delete statement affected an unexpected number
of rows (0). Entities may have been modified or deleted since entities were
loaded. See http://go.microsoft.com/fwlink/?LinkId=472540 for information on
understanding and handling optimistic concurrency exceptions.
Výpis: v
System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.ValidateRowsAffected(Int64
rowsAffected, UpdateCommand source) v
System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.Update() v
System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1
func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction,
Boolean releaseConnectionOnSuccess) v
System.Data.Entity.Core.Objects.ObjectContext.SaveChangesToStore(SaveOptions
options, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction)
v System.Data.Entity.Core.Objects.ObjectContext.SaveChangesInternal(SaveOptions
options, Boolean executeInExistingTransaction) v
System.Data.Entity.Internal.InternalContext.SaveChanges()
----
Suggested Fix:
Instead of simple unconditional calling of SUSPEND we made minor change to the
DmlSqlGenerator.GenerateReturningSql() method:
...
if (row_count > 0) then SUSPEND;
commandText.AppendLine("END");
...
if UPDATE command in EXECUTE BLOCK succeeded then Firebird Server sets
row_count to 1 and then we sent the row to the caller, otherwise we do nothing
(caller obtains empty result set). According Firebird database manual, the
row_count should be supported since FB 1.5+ and it should not be too limiting
for today deployments.
EF then gets empty result set and correctly detects it as
DbConecurrencyException. We did minor testing and it looks promising.
Affected provider versions (where seen): 4.7.0.0, 5.1.1.0 and maybe others if
GenerateReturningSql() generates the same pattern.
Jiri Fartak, WMS s.r.o.
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