Help with a nokogiri XML parse

[Jason Chodakowski]

Hi,

I'm trying to parse and alter an log4net.xml configuration file. Specifically, I'm having trouble referencing this part of the DOM:

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

  <log4net>

   <appender name="XmlAppender" type="log4net.Appender.RollingFileAppender">

      <file type="log4net.Util.PatternString" value="some_ouput_log.xml" />

      <appendToFile value="true" />

      <rollingStyle value="Size" />

      <maxSizeRollBackups value="100" />

      <maximumFileSize value="10MB" />

      <staticLogFileName value="true" />

      <layout type="log4net.Layout.XmlLayoutSchemaLog4j">

        <locationInfo value="true" />

      </layout>

   </appender>

 </log4net>
</configuration>

I'm trying to codify a xpath_at to the maxSizeRollBackups attribute/node. Any guidance would be most appreciated.

Thanks

[Walter Lee Davis]

On Oct 22, 2015, at 3:26 PM, Jason Chodakowski <jgchod...@gmail.com> wrote:

> Hi,
>
> I'm trying to parse and alter an log4net.xml configuration file. Specifically, I'm having trouble referencing this part of the DOM:
>
> <?xml version="1.0" encoding="utf-8" ?>
> <configuration>
> <log4net>
> <appender name="XmlAppender" type="log4net.Appender.RollingFileAppender">
> <file type="log4net.Util.PatternString" value="some_ouput_log.xml" />
> <appendToFile value="true" />
> <rollingStyle value="Size" />
> <maxSizeRollBackups value="100" />
> <maximumFileSize value="10MB" />
> <staticLogFileName value="true" />
> <layout type="log4net.Layout.XmlLayoutSchemaLog4j">
> <locationInfo value="true" />
> </layout>
> </appender>
> </log4net>
> </configuration>
>

Is this part of the file, or the entire file?

> I'm trying to codify a xpath_at to the maxSizeRollBackups attribute/node. Any guidance would be most appreciated.

You could try using css_at instead, that's often much simpler to write. To get the first instance of maxSizeRollBackups out of any given file, you would just do:

doc = Nokogiri::XML.parse(your_document_as_a_string)
backups_node = doc.at_css('maxSizeRollBackups')
backups = backups_node._value if backups_node

The underscore trick lets you reference an attribute that has the same name as a core Noko method. You could also use backups_node['value'] if that's clearer for you.

Walter

>
> Thanks
>
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[Robert Klemme]

Contrary to Walter I prefer XPath:

Preparation

irb(main):001:0> doc=<<'XML'

irb(main):002:0' <?xml version="1.0" encoding="utf-8" ?>

</configuration>

irb(main):003:0' <configuration>

...

irb(main):019:0> dom = Nokogiri.XML(doc)

=> #<Nokogiri::XML::Document:0x3001ff9d4 name="document" children=[#<Nokogiri::XML::Element:0x3001ff538 name="configuration" children=[#<Nokogiri::XML::Text:0x3001ff2a4 "\n  ">, #<Nokogiri::XML::Element:0x3001ff164 name="log4net" children=[#<Nokogiri::XML::Text:0x

...

Here are a few ways - from simple to more complex:

irb(main):041:0> dom.at_xpath '//maxSizeRollBackups'

=> #<Nokogiri::XML::Element:0x3001f829c name="maxSizeRollBackups" attributes=[#<Nokogiri::XML::Attr:0x3001f81fc name="value" value="100">]>

irb(main):042:0> puts dom.at_xpath '//maxSizeRollBackups'

<maxSizeRollBackups value="100"/>

=> nil

irb(main):043:0> puts dom.at_xpath '/configuration/log4net/appender/maxSizeRollBackups'

<maxSizeRollBackups value="100"/>

=> nil

irb(main):044:0> puts dom.at_xpath '/configuration/log4net/appender[@type="log4net.Appender.RollingFileAppender"]/maxSizeRollBackups'

<maxSizeRollBackups value="100"/>

=> nil

Which you use depends on the remainder of the file and the task that you want to fulfill.

Kind regards

robert