Re: Optimistic locking failure on insert
Re: Optimistic locking failure on insert
- Subject: Re: Optimistic locking failure on insert
- From: Chuck Hill <email@hidden>
- Date: Wed, 15 Mar 2006 09:41:07 -0800
Hi,
On Mar 15, 2006, at 7:31 AM, Jerry W. Walker wrote:
Hi, Ian,
I can't imagine (short of a bug in the development environment) how
the code you're exposing below could cause an optimistic locking
failure. The upshot of the code below only reads from the store. It
neither creates nor updates any records therein.
Optimistic locking failures occur on an attempt to write a record
to the database when the record on the database into which you're
trying to write has data other than what you expected to be there.
This is typically caused by someone else writing into the same
record before you, but can also be caused by rounding errors in
fields your checking for the optimistic locking check (e.g.
including Doubles or Date fields among the optimistic lock check
fields).
Hold on a second here. Ian is using JavaClient and that complicates
this a bit. As the clients are disconnected from the EOF stack, they
don't get notifications of "objects changed in store" such as are
broadcast in the WebObjects application proper. So it is also
possible that an optimistic locking exception could occur when Client
A's request gets to the server and Client B has updated that object
since it was sent out to Client A. EOF would (should) see that
Client A's snapshot does not match the snapshot in the object store
and produce this exception. This is what the message seems to be
suggesting:
The object with global ID <EOTemporaryGlobalID: 0 0 -64 -88 0 7 0
0 -15 83 1 0 0 0 1 9 -9 81 65 -102 58 -107 -26 -116> has been
changed by another client
Now, that does not explain how this is happening on a newly inserted
object. Hence, I will resort to wild speculation. ;-)
1) A snapshot for the object has been registered on the server under
this temporary ID prior to this save and some server side code has
changed some value and this change was not seen by the client.
awakeFromInsertion? When the save happens the snapshot does not
match what the client has
2) Somehow duplicate EOTemporaryGlobalID's are getting generated.
This seems too implausible to even consider.
On Mar 14, 2006, at 11:54 PM, Ian Joyner wrote:
OK, found the problem. It was not in the model, but rather in the
code for initializing a JTree. First, I was getting top-level
nodes by getting them out of the display group:
NSArray notes = EOQualifier.filteredArrayWithQualifier
(display_group.allObjects (),
EOQualifier.qualifierWithQualifierFormat ("parent_note = null",
null));
however, sometimes the display group had not fetched yet, so I
used a fetch spec to go straight to the DB:
NSArray notes = editing_context.objectsWithFetchSpecification (new
EOFetchSpecification ("Note", new EOAndQualifier (new NSArray (new
Object [] {EOQualifier.qualifierWithQualifierFormat ("parent_note
= null", null), EOQualifier.qualifierWithQualifierFormat ("owner =
%@", new NSArray (new Object []
{owning_display_group.selectedObject ()}))})), null));
Is there more than one editing context in play here? Is it possible
that you have somehow got the same new object registered in _two_
editing contexts?
The above statement is more difficult to read than it needs to be.
You can use "AND" directly in the qualifierWithQualifierFormat method.
For some reason, which I'd like an explanation for, this caused
the optimistic locking problem when creating a new master record.
So then I realised the most straight forward solution was to
traverse the object path:
NSArray notes = EOQualifier.filteredArrayWithQualifier (((Artifact)
owning_display_group.selectedObject ()).notes (),
EOQualifier.qualifierWithQualifierFormat ("parent_note = null",
null));
That does sort of sound like a crossed editing context problem. I
don't see where the new object is coming into play though.
Is editing_context == owning_display_group.selectedObject
().editingContext()?
(The fetch spec code probably would have been better in Haskell,
but I dislike assigning things to temporary variables in Java when
the code could be more functional.)
I generally find that temporary variables can add greatly to the
semantic value of the code. It can make the code significantly more
readable. How does leaving them out make the code more functional?
Perhaps more functional is a British term for less readable? :-P As
a "write seldom, read often" artifact, I value readability over
almost everything else.
Don't know if this little note may help anyone in the future,
because I still don't know the link between the fetch spec and the
optimistic locking failure (and I hate the hacking until it
happens to work approach).
In looking over the debugging statements below, it looks like there
is an attempt to save a member record which contains itself as a
member.
Good catch Jerry!
That is, it looks like the inserted record has the following
recursive structure:
MemberRecord:
details = null
begin_date = 3/14/2006 @ 5:53:51 GMT
position = null
member = <self reference> ************ IS THIS CORRECT?
****************
end_date = null
group = Groups: {
<some not-yet-saved GroupMember>
}
person = null
title = <reference to previously saved title with PK = 1>
telephones = ()
modification_date = 3/14/2006 @ 5:53:51 GMT
I can certainly imagine problems with such a structure, if I'm
inferring correctly.
I don't see how exactly it would cause the exception, but it
certainly looks suspicious.
Have you turned on EOAdaptorDebuggingEnabled to check the generated
SQL? It looks like EOF may be attempting to write a record that
contains itself recursively and determines on the second recursion
that the record has already been written. That would be my guess
without seeing the SQL.
Ian said, "No SQL commands are being executed in the SQL trace.". It
is not getting that far.
Chuck
Ian
On 14/03/2006, at 5:09 PM, Ian Joyner wrote:
I have been running this model for six months and saving this
entity just fine. Suddenly, I am getting an optimistic locking
failure when doing an insert of a new record (that's right
insert, not update). In fact is the trace below, I show that the
offending record is in the editing contexts insertedObjects and
it has a EOTemporaryGlobalID which means it has not been written
to the database yet.
No SQL commands are being executed in the SQL trace. I have
turned off locking on every attribute for this entity in
EOModeler. Other entities are still saving fine. So what's going
on? How can I get around this problem?
[2006-03-14 16:53:56 EST] <AWT-EventQueue-0>
xxx.client.Member_interface_controller save inserted ({values =
{details = <com.webobjects.foundation.NSKeyValueCoding$Null>;
begin_date = 2006-03-14 05:53:51 Etc/GMT; position =
<com.webobjects.foundation.NSKeyValueCoding$Null>; member =
"<com.sportstec.member.client.Member f1156e <EOTemporaryGlobalID:
0 0 -64 -88 0 7 0 0 -15 83 1 0 0 0 1 9 -9 81 65 -102 58 -107 -26
-116>>"; end_date = <com.webobjects.foundation.NSKeyValueCoding
$Null>; group = "<com.sportstec.group.client.Group 47545b groups
= ("<com.sportstec.group.client.Group_Member 8dacbb
<EOTemporaryGlobalID: 0 0 -64 -88 0 7 0 0 -15 83 2 0 0 0 1 9 -9
81 65 -102 58 -107 -26 -116>>"); person = "null"; title =
"<com.webobjects.eocontrol.EOGenericRecord dd1d62
_EOIntegralKeyGlobalID[Title (java.lang.Integer)1]>"; telephones
= (); modification_date = 2006-03-14 05:53:51 Etc/GMT; }; this =
"<com.sportstec.member.client.Member f1156e <EOTemporaryGlobalID:
0 0 -64 -88 0 7 0 0 -15 83 1 0 0 0 1 9 -9 81 65 -102 58 -107 -26
-116>>"; })
[2006-03-14 16:53:56 EST] <AWT-EventQueue-0>
xxx.client.Member_interface_controller save updated (Gq)
[2006-03-14 16:53:56 EST] <AWT-EventQueue-0>
xxx.client.Member_interface_controller save deleted ()
[2006-03-14 16:53:56 EST] <AWT-EventQueue-0>
xxx.client.Member_interface_controller EditingContext saveChanges
failed Server exception: Optimistic locking failure: The object
with global ID <EOTemporaryGlobalID: 0 0 -64 -88 0 7 0 0 -15 83 1
0 0 0 1 9 -9 81 65 -102 58 -107 -26 -116> has been changed by
another client
Thanks
Ian Joyner
Sportstec
--
__ Jerry W. Walker,
WebObjects Developer/Instructor for High Performance Industrial
Strength Internet Enabled Systems
email@hidden
203 278-4085 office
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