xmerl_xpath difficulties
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xmerl_xpath difficulties
by David Mitchell-5
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Hello group,
I'm having trouble getting my head around xmerl_xpath - I've gone through a bunch of Google searches, but can't find the "Simple guide to xmerl_xpath" I'm looking for ;-> I've reduced my problem to 3 lines of code: 15> {XmlFull, _} = xmerl_scan:string("<text>Hello</text>"). {{xmlElement,text, text, [], {xmlNamespace,[],[]}, [], 1, [], [{xmlText,[{text,1}],1,[],"Hello",text}], [], "/home/davidm", undeclared}, []} 16> xmerl:export([XmlFull], xmerl_xml). ["<?xml version=\"1.0\"?>",[[["<","text",">"],["Hello"],["</","text",">"]]]] 17> xmerl_xpath:string("//text/*", XmlFull). [] Line 16 seems to confirm that XmlFull contains my XML string. However, I'd expect line 17 to give me something like "Hello" or ["Hello"], yet it returns an empty list. Could someone please point out the (no doubt very simple) mistake I've made? Also, if a "Simple guide to xmerl_xpath" exists somewhere, could someone please point me towards it? Thanks in advance Dave M. _______________________________________________ erlang-questions mailing list erlang-questions@... http://www.erlang.org/mailman/listinfo/erlang-questions |
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Re: xmerl_xpath difficulties
by Jeremy Thurgood
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David Mitchell wrote:
> I'm having trouble getting my head around xmerl_xpath - I've gone > through a bunch of Google searches, but can't find the "Simple guide > to xmerl_xpath" I'm looking for ;-> You might want to look at the W3C's xpath tutorial at http://www.w3schools.com/xpath/default.asp > I've reduced my problem to 3 lines of code: > > 15> {XmlFull, _} = xmerl_scan:string("<text>Hello</text>"). > {{xmlElement,text, > text, > [], > {xmlNamespace,[],[]}, > [], > 1, > [], > [{xmlText,[{text,1}],1,[],"Hello",text}], > [], > "/home/davidm", > undeclared}, > []} > > 16> xmerl:export([XmlFull], xmerl_xml). > ["<?xml version=\"1.0\"?>",[[["<","text",">"],["Hello"],["</","text",">"]]]] > > 17> xmerl_xpath:string("//text/*", XmlFull). > [] > > > Line 16 seems to confirm that XmlFull contains my XML string. > However, I'd expect line 17 to give me something like "Hello" or > ["Hello"], yet it returns an empty list. You're asking it for xml elements below <text>, of which there are none. 5> xmerl_xpath:string("//text/text()", XmlFull). [{xmlText,[{text,1}],1,[],"Hello",text}] Look like you'll still have to extract the string from the #xmlText record. HTH, --J _______________________________________________ erlang-questions mailing list erlang-questions@... http://www.erlang.org/mailman/listinfo/erlang-questions |
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Re: xmerl_xpath difficulties
by dcaoyuan
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It's a bit strange, it works in my computer. You may try:
1> {XmlFull, _} = xmerl_scan:string("<text>Hello</text>"). {{xmlElement,text, text, [], {xmlNamespace,[],[]}, [], 1, [], [{xmlText,[{text,1}],1,[],"Hello",text}], [], "/Users/dcaoyuan/polebeans/ewp", undeclared}, []} 2> XmlTexts = xmerl_xpath:string("/text/text()", XmlFull). [{xmlText,[{text,1}],1,[],"Hello",text}] The xpath query should return a list of result, it maybe [], or more than one element, so it's better to do: 3> lists:flatten([element(5,X) || X <- XmlTexts, element(1, X) == xmlText]). "Hello" If you are in writing a module, by including xmerl.hrl, you can: lists:flatten([X#xmlText.value || X <- XmlTexts, is_record(X, xmlText)]). On 8/5/07, David Mitchell <monch1962@...> wrote: > Thanks Caoyuan, but it didn't work for me: > > davidm@davidm-desktop:~$ erl > Erlang (BEAM) emulator version 5.4.9 [64-bit] [source] [threads:0] > > Eshell V5.4.9 (abort with ^G) > 1> {XmlFull,_} = xmerl_scan:string("<text>Hello</text>"). > {{xmlElement,text, > text, > [], > {xmlNamespace,[],[]}, > [], > 1, > [], > [{xmlText,[{text,1}],1,[],"Hello",text}], > [], > "/home/davidm", > undeclared}, > []} > 2> [XmlText] = xmerl_xpath:string("/text/text()", XmlFull). > > =ERROR REPORT==== 5-Aug-2007::22:48:45 === > Error in process <0.31.0> with exit value: {{badmatch,[]},[{erl_eval,expr,3}]} > > ** exited: {{badmatch,[]},[{erl_eval,expr,3}]} ** > 3> > > Any thoughts? > > Regards > > Dave M. > > On 05/08/07, Caoyuan <dcaoyuan@...> wrote: > > > [XmlText] = xmerl_xpath:string("/text/text()", XmlFull). > > [{xmlText,[{text,1}],1,[],"Hello",text}] > > > element(5, XmlText). > > "Hello" > > > > > > On 8/5/07, David Mitchell <monch1962@...> wrote: > > > Hello group, > > > > > > I'm having trouble getting my head around xmerl_xpath - I've gone > > > through a bunch of Google searches, but can't find the "Simple guide > > > to xmerl_xpath" I'm looking for ;-> > > > > > > I've reduced my problem to 3 lines of code: > > > > > > 15> {XmlFull, _} = xmerl_scan:string("<text>Hello</text>"). > > > {{xmlElement,text, > > > text, > > > [], > > > {xmlNamespace,[],[]}, > > > [], > > > 1, > > > [], > > > [{xmlText,[{text,1}],1,[],"Hello",text}], > > > [], > > > "/home/davidm", > > > undeclared}, > > > []} > > > > > > 16> xmerl:export([XmlFull], xmerl_xml). > > > ["<?xml version=\"1.0\"?>",[[["<","text",">"],["Hello"],["</","text",">"]]]] > > > > > > 17> xmerl_xpath:string("//text/*", XmlFull). > > > [] > > > > > > > > > Line 16 seems to confirm that XmlFull contains my XML string. > > > However, I'd expect line 17 to give me something like "Hello" or > > > ["Hello"], yet it returns an empty list. > > > > > > Could someone please point out the (no doubt very simple) mistake I've > > > made? Also, if a "Simple guide to xmerl_xpath" exists somewhere, > > > could someone please point me towards it? > > > > > > Thanks in advance > > > > > > Dave M. > > > _______________________________________________ > > > erlang-questions mailing list > > > erlang-questions@... > > > http://www.erlang.org/mailman/listinfo/erlang-questions > > > > > > > > > -- > > - Caoyuan > > > _______________________________________________ > erlang-questions mailing list > erlang-questions@... > http://www.erlang.org/mailman/listinfo/erlang-questions > -- - Caoyuan _______________________________________________ erlang-questions mailing list erlang-questions@... http://www.erlang.org/mailman/listinfo/erlang-questions |
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Re: xmerl_xpath difficulties
by David Mitchell-5
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Thanks again Caoyuan,
OK, I think I've got it - there's a bug in Erlang on Ubuntu 6.06. No idea if it's a bug in Erlang itself (i.e. version 5.4.9 vs. 5.5.5), or a bug in the implementation of Erlang in Ubuntu, but it seems pretty straightforward. The Windows version works OK, but the Ubuntu version doesn't. Here's 2 sessions: the first on Ubuntu and the 2nd on Windows davidm@davidm-desktop:~$ erl Erlang (BEAM) emulator version 5.4.9 [64-bit] [source] [threads:0] Eshell V5.4.9 (abort with ^G) 1> {XmlFull,_} = xmerl_scan:string("<text>Hello</text>"). {{xmlElement,text, text, [], {xmlNamespace,[],[]}, [], 1, [], [{xmlText,[{text,1}],1,[],"Hello",text}], [], "/home/davidm", undeclared}, []} 2> XmlText = xmerl_xpath:string("/text/text()", XmlFull). [] 3> lists:flatten([element(5,X)|| X <- XmlTexts, element(1,X) == xmlText]). [] 4> Now the Windows version: D:\Program Files\erl5.5.5\bin>erl Eshell V5.5.5 (abort with ^G) 1> {XmlFull, _} = xmerl_scan:string("<text>Hello</text>"). {{xmlElement,text, text, [], {xmlNamespace,[],[]}, [], 1, [], [{xmlText,[{text,1}],1,[],"Hello",text}], [], "D:/Program Files/erl5.5.5/bin", undeclared}, []} 2> XmlText = xmerl_xpath:string("/text/text()", XmlFull). [{xmlText,[{text,1}],1,[],"Hello",text}] 3> Note the difference in the value of XmlText in both cases - this is a fairly trivial issue to reproduce, being only 2 lines of code. I'm still finding my feet in the Erlang world - can someone pls give me a pointer as to how I should file a bug report on this? Even if it doesn't get fixed, I'd like it documented (and searchable) so that the next person who stumbles on it doesn't get bogged down as I did. Thanks to everyone for their help tracking this down. Regards Dave M. On 05/08/07, Caoyuan <dcaoyuan@...> wrote: > It's a bit strange, it works in my computer. You may try: > 1> {XmlFull, _} = xmerl_scan:string("<text>Hello</text>"). > {{xmlElement,text, > text, > [], > {xmlNamespace,[],[]}, > [], > 1, > [], > [{xmlText,[{text,1}],1,[],"Hello",text}], > [], > "/Users/dcaoyuan/polebeans/ewp", > undeclared}, > []} > 2> XmlTexts = xmerl_xpath:string("/text/text()", XmlFull). > [{xmlText,[{text,1}],1,[],"Hello",text}] > > The xpath query should return a list of result, it maybe [], or more > than one element, so it's better to do: > > 3> lists:flatten([element(5,X) || X <- XmlTexts, element(1, X) == xmlText]). > "Hello" > > If you are in writing a module, by including xmerl.hrl, you can: > lists:flatten([X#xmlText.value || X <- XmlTexts, is_record(X, xmlText)]). > > > On 8/5/07, David Mitchell <monch1962@...> wrote: > > Thanks Caoyuan, but it didn't work for me: > > > > davidm@davidm-desktop:~$ erl > > Erlang (BEAM) emulator version 5.4.9 [64-bit] [source] [threads:0] > > > > Eshell V5.4.9 (abort with ^G) > > 1> {XmlFull,_} = xmerl_scan:string("<text>Hello</text>"). > > {{xmlElement,text, > > text, > > [], > > {xmlNamespace,[],[]}, > > [], > > 1, > > [], > > [{xmlText,[{text,1}],1,[],"Hello",text}], > > [], > > "/home/davidm", > > undeclared}, > > []} > > 2> [XmlText] = xmerl_xpath:string("/text/text()", XmlFull). > > > > =ERROR REPORT==== 5-Aug-2007::22:48:45 === > > Error in process <0.31.0> with exit value: {{badmatch,[]},[{erl_eval,expr,3}]} > > > > ** exited: {{badmatch,[]},[{erl_eval,expr,3}]} ** > > 3> > > > > Any thoughts? > > > > Regards > > > > Dave M. > > > > On 05/08/07, Caoyuan <dcaoyuan@...> wrote: > > > > [XmlText] = xmerl_xpath:string("/text/text()", XmlFull). > > > [{xmlText,[{text,1}],1,[],"Hello",text}] > > > > element(5, XmlText). > > > "Hello" > > > > > > > > > On 8/5/07, David Mitchell <monch1962@...> wrote: > > > > Hello group, > > > > > > > > I'm having trouble getting my head around xmerl_xpath - I've gone > > > > through a bunch of Google searches, but can't find the "Simple guide > > > > to xmerl_xpath" I'm looking for ;-> > > > > > > > > I've reduced my problem to 3 lines of code: > > > > > > > > 15> {XmlFull, _} = xmerl_scan:string("<text>Hello</text>"). > > > > {{xmlElement,text, > > > > text, > > > > [], > > > > {xmlNamespace,[],[]}, > > > > [], > > > > 1, > > > > [], > > > > [{xmlText,[{text,1}],1,[],"Hello",text}], > > > > [], > > > > "/home/davidm", > > > > undeclared}, > > > > []} > > > > > > > > 16> xmerl:export([XmlFull], xmerl_xml). > > > > ["<?xml version=\"1.0\"?>",[[["<","text",">"],["Hello"],["</","text",">"]]]] > > > > > > > > 17> xmerl_xpath:string("//text/*", XmlFull). > > > > [] > > > > > > > > > > > > Line 16 seems to confirm that XmlFull contains my XML string. > > > > However, I'd expect line 17 to give me something like "Hello" or > > > > ["Hello"], yet it returns an empty list. > > > > > > > > Could someone please point out the (no doubt very simple) mistake I've > > > > made? Also, if a "Simple guide to xmerl_xpath" exists somewhere, > > > > could someone please point me towards it? > > > > > > > > Thanks in advance > > > > > > > > Dave M. > > > > _______________________________________________ > > > > erlang-questions mailing list > > > > erlang-questions@... > > > > http://www.erlang.org/mailman/listinfo/erlang-questions > > > > > > > > > > > > > -- > > > - Caoyuan > > > > > _______________________________________________ > > erlang-questions mailing list > > erlang-questions@... > > http://www.erlang.org/mailman/listinfo/erlang-questions > > > > > -- > - Caoyuan > erlang-questions mailing list erlang-questions@... http://www.erlang.org/mailman/listinfo/erlang-questions |
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