Re: Optimistic locking failure on insert
Re: Optimistic locking failure on insert
- Subject: Re: Optimistic locking failure on insert
- From: "Jerry W. Walker" <email@hidden>
- Date: Wed, 15 Mar 2006 15:27:10 -0500
On Mar 15, 2006, at 12:41 PM, Chuck Hill wrote:
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.
Agreed that this is JavaClient, but I'm not sure how that invalidates
anything stated before. It simply allows the "someone else" I
mentioned to exist within the same application without intentionally
creating a new EO Stack.
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.
I'm guessing here, since I've never tried to create and then persist
an object graph that recurses onto itself, but might it attempt to
write the record as it first puts the inserted record into the
database, then try to update that same record as it recurses across
the relationship, identifying the record as changed from what it
assumed would be there?
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.
Yeah, I'm not sure I understand that either, since it seems to me
that an optimistic locking failure could not have occurred until the
attempt was made to insert/update the record on the database. My
understanding is that the optimistic locking failure occurs when the
SQL "WHERE" clause fails to match the record in the database.
The SQL would have had to have been generated (and executed) for that
to occur.
Am I missing something here?
Regards,
Jerry
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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