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Posted to user@commons.apache.org by Warren Liang <wl...@gmail.com> on 2008/01/25 18:33:38 UTC
JXPath and circular object graphs
Hi all,
How does JXPath handle circular object paths? My object graph is can
have circular references to objects that are the same instance (i.e.
obj1 == obj2), or are different instances but have equivalent values
(i.e. obj1.equals(obj2))
Right now, I'm evaluating JXPath expressions that do not match
anything in the object graph and it seems like it's going through an
infinite loop. Some of my expressions use the "match anywhere"
operator (i.e. //).
Does JXPath use a breadth first search or a depth first search through
the object graph?
Ideally, I'd be able to tell JXPath to recurse a maximum depth, or to
recognize that a node has already been traversed Are there hooks for
me to do this?
Thanks,
Warren Liang
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Re: [JXPath] circular object graphs
Posted by Matt Benson <gu...@yahoo.com>.
--- Warren Liang <wl...@gmail.com> wrote:
> Thanks Matt for your response :).
>
> I believe that JXPath is working the way that it's
> supposed to in
> regards to what I'm doing.
>
> I think I'm going to try out a
> DynamicPropertyHandler that will return
> a list of no properties if I'm encountering an
> object that I've
> already encountered before. I'm guessing that this
> will require me to
> create a Set that will keep track of all of the
> nodes that I've
> already encountered.
>
> Hopefully, I'll be able to implement a breadth first
> search by
> customizing NodeIterator (I hope that's the right
> hook).
>
If you come up with anything interesting, feel free to
post it on the Wiki.
br,
Matt
> Thanks,
>
> Warren
>
> On Jan 25, 2008 9:50 AM, Matt Benson
> <gu...@yahoo.com> wrote:
> >
> > --- Warren Liang <wl...@gmail.com> wrote:
> >
> > > Hi all,
> > >
> > > How does JXPath handle circular object paths?
> My
> > > object graph is can
> > > have circular references to objects that are the
> > > same instance (i.e.
> > > obj1 == obj2), or are different instances but
> have
> > > equivalent values
> > > (i.e. obj1.equals(obj2))
> > >
> > > Right now, I'm evaluating JXPath expressions
> that do
> > > not match
> > > anything in the object graph and it seems like
> it's
> > > going through an
> > > infinite loop. Some of my expressions use the
> > > "match anywhere"
> > > operator (i.e. //).
> >
> > If you are encountering behavior that feels wrong
> to
> > you, feel welcome to open an issue in JIRA,
> preferably
> > with some sample code that can easily be turned
> into a
> > standalone JUnit test.
> >
> > >
> > > Does JXPath use a breadth first search or a
> depth
> > > first search through
> > > the object graph?
> > >
> >
> > In my experience, not being the original author of
> the
> > code, JXPath determines matching nodes for a given
> > level, then applies subsequent levels in
> > recursive-descent fashion to each node selected at
> the
> > current level. So given:
> >
> > <a>
> > <b>
> > <c /><c />
> > </b>
> > <b>
> > <c /><c />
> > </b>
> > <b>
> > <c /><c />
> > </b>
> > </a>
> >
> > and path "/a/b/c", JXPath will determine that a[1]
> > matches the first step and apply the next step.
> Now
> > it determines that a[1]/b[1], a[1]/b[2] and
> a[1]/b[3]
> > match the second step. Then it applies the third
> step
> > to a[1]/b[1], a[1]/b[2], and a[1]/b[3] in
> succession.
> > I interpret this as being depth first.
> >
> > > Ideally, I'd be able to tell JXPath to recurse a
> > > maximum depth, or to
> > > recognize that a node has already been traversed
> > > Are there hooks for
> > > me to do this?
> > >
> >
> > I suppose nothing would ever stop you from
> > implementing a custom "I haven't seen this before"
> > function to guard each step, but it might get a
> little
> > heavy at RT depending on the size of your graph.
> Off
> > the top of my head I can't remember what, if any,
> > safeguards are built into JXPath to prevent
> infinite
> > recursion, hence my initial suggestion (and
> attempt to
> > put the onus onto you ;) ) that you submit reports
> for
> > problems encountered.
> >
> > Is any of this helpful whatsoever?
> > -Matt
> >
> > > Thanks,
> > >
> > > Warren Liang
> > >
> > >
> >
>
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> > > user-unsubscribe@commons.apache.org
> > > For additional commands, e-mail:
> > > user-help@commons.apache.org
> > >
> > >
> >
> >
> >
> >
>
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Re: [JXPath] circular object graphs
Posted by Warren Liang <wl...@gmail.com>.
Thanks Matt for your response :).
I believe that JXPath is working the way that it's supposed to in
regards to what I'm doing.
I think I'm going to try out a DynamicPropertyHandler that will return
a list of no properties if I'm encountering an object that I've
already encountered before. I'm guessing that this will require me to
create a Set that will keep track of all of the nodes that I've
already encountered.
Hopefully, I'll be able to implement a breadth first search by
customizing NodeIterator (I hope that's the right hook).
Thanks,
Warren
On Jan 25, 2008 9:50 AM, Matt Benson <gu...@yahoo.com> wrote:
>
> --- Warren Liang <wl...@gmail.com> wrote:
>
> > Hi all,
> >
> > How does JXPath handle circular object paths? My
> > object graph is can
> > have circular references to objects that are the
> > same instance (i.e.
> > obj1 == obj2), or are different instances but have
> > equivalent values
> > (i.e. obj1.equals(obj2))
> >
> > Right now, I'm evaluating JXPath expressions that do
> > not match
> > anything in the object graph and it seems like it's
> > going through an
> > infinite loop. Some of my expressions use the
> > "match anywhere"
> > operator (i.e. //).
>
> If you are encountering behavior that feels wrong to
> you, feel welcome to open an issue in JIRA, preferably
> with some sample code that can easily be turned into a
> standalone JUnit test.
>
> >
> > Does JXPath use a breadth first search or a depth
> > first search through
> > the object graph?
> >
>
> In my experience, not being the original author of the
> code, JXPath determines matching nodes for a given
> level, then applies subsequent levels in
> recursive-descent fashion to each node selected at the
> current level. So given:
>
> <a>
> <b>
> <c /><c />
> </b>
> <b>
> <c /><c />
> </b>
> <b>
> <c /><c />
> </b>
> </a>
>
> and path "/a/b/c", JXPath will determine that a[1]
> matches the first step and apply the next step. Now
> it determines that a[1]/b[1], a[1]/b[2] and a[1]/b[3]
> match the second step. Then it applies the third step
> to a[1]/b[1], a[1]/b[2], and a[1]/b[3] in succession.
> I interpret this as being depth first.
>
> > Ideally, I'd be able to tell JXPath to recurse a
> > maximum depth, or to
> > recognize that a node has already been traversed
> > Are there hooks for
> > me to do this?
> >
>
> I suppose nothing would ever stop you from
> implementing a custom "I haven't seen this before"
> function to guard each step, but it might get a little
> heavy at RT depending on the size of your graph. Off
> the top of my head I can't remember what, if any,
> safeguards are built into JXPath to prevent infinite
> recursion, hence my initial suggestion (and attempt to
> put the onus onto you ;) ) that you submit reports for
> problems encountered.
>
> Is any of this helpful whatsoever?
> -Matt
>
> > Thanks,
> >
> > Warren Liang
> >
> >
> ---------------------------------------------------------------------
> > To unsubscribe, e-mail:
> > user-unsubscribe@commons.apache.org
> > For additional commands, e-mail:
> > user-help@commons.apache.org
> >
> >
>
>
>
> ____________________________________________________________________________________
> Never miss a thing. Make Yahoo your home page.
> http://www.yahoo.com/r/hs
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: user-unsubscribe@commons.apache.org
> For additional commands, e-mail: user-help@commons.apache.org
>
>
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Re: [JXPath] circular object graphs
Posted by Matt Benson <gu...@yahoo.com>.
--- Warren Liang <wl...@gmail.com> wrote:
> Hi all,
>
> How does JXPath handle circular object paths? My
> object graph is can
> have circular references to objects that are the
> same instance (i.e.
> obj1 == obj2), or are different instances but have
> equivalent values
> (i.e. obj1.equals(obj2))
>
> Right now, I'm evaluating JXPath expressions that do
> not match
> anything in the object graph and it seems like it's
> going through an
> infinite loop. Some of my expressions use the
> "match anywhere"
> operator (i.e. //).
If you are encountering behavior that feels wrong to
you, feel welcome to open an issue in JIRA, preferably
with some sample code that can easily be turned into a
standalone JUnit test.
>
> Does JXPath use a breadth first search or a depth
> first search through
> the object graph?
>
In my experience, not being the original author of the
code, JXPath determines matching nodes for a given
level, then applies subsequent levels in
recursive-descent fashion to each node selected at the
current level. So given:
<a>
<b>
<c /><c />
</b>
<b>
<c /><c />
</b>
<b>
<c /><c />
</b>
</a>
and path "/a/b/c", JXPath will determine that a[1]
matches the first step and apply the next step. Now
it determines that a[1]/b[1], a[1]/b[2] and a[1]/b[3]
match the second step. Then it applies the third step
to a[1]/b[1], a[1]/b[2], and a[1]/b[3] in succession.
I interpret this as being depth first.
> Ideally, I'd be able to tell JXPath to recurse a
> maximum depth, or to
> recognize that a node has already been traversed
> Are there hooks for
> me to do this?
>
I suppose nothing would ever stop you from
implementing a custom "I haven't seen this before"
function to guard each step, but it might get a little
heavy at RT depending on the size of your graph. Off
the top of my head I can't remember what, if any,
safeguards are built into JXPath to prevent infinite
recursion, hence my initial suggestion (and attempt to
put the onus onto you ;) ) that you submit reports for
problems encountered.
Is any of this helpful whatsoever?
-Matt
> Thanks,
>
> Warren Liang
>
>
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> To unsubscribe, e-mail:
> user-unsubscribe@commons.apache.org
> For additional commands, e-mail:
> user-help@commons.apache.org
>
>
____________________________________________________________________________________
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