[Twisted-web] how are solving the calls to the children in nevow?

[Alberto Trujillo]

Thank you very much Matt for this brief tutorial or personal class. It 
helped me a lot.

Matt Goodall wrote:

>Alberto Trujillo wrote:
>
>  
>
>>Hello:
>>I have been following this example
>>"http://nevowexamples.adytum.us/childrenhtml/"to know how works the
>>calls to the children with nevow, but still it's not enough clear for me.
>>
>>I even add a new child in the childFactory and some print command to
>>follow the way of the calls. Here I show you my modifications:
>>
>>   def childFactory(self, ctx, name):
>>       print "NAME = " + name
>>       if name in ['1', '2', '3']:
>>           return ChildPage(name)
>>       elif name == 'one':
>>           return OneRoot()
>>
>>   def locateChild(self, ctx, segments):
>>       child, remainingSegments = rend.Page.locateChild(self, ctx,
>>segments)
>>       print "CHILD = " + str(child) + " SEGMENT = " +
>>str(remainingSegments)
>>       if child:
>>           print "IN THE IF"
>>           return child, remainingSegments
>>
>>       return ChildPage('/'.join(segments)), []
>>
>>My question is why each time that I call to "one" it goes inside
>>"locateChild" wheter "one" is place in "childFactory", here is a trace
>>of my server.
>>    
>>
>
>Only locateChild(self, context, segments) is part of the IResource API.
>All the child_ and childFactory support is provided by the
>rend.ChildLookupMixin class that rend.Page subclasses.
>
>What's happening in the above code is that you have an overridden
>locateChild method that calls rend.Page.locateChild.
>rend.Page.locateChild does the child_ and childFactory magic and calls
>your childFactory method. Your childFactory prints the NAME and returns
>the child resource back to your locateChild method which then also
>prints it out as CHILD.
>
>  
>
>>2005/07/07 13:52 IST [HTTPChannel,0,127.0.0.1] NAME = one
>>2005/07/07 13:52 IST [HTTPChannel,0,127.0.0.1] CHILD = <one.OneRoot
>>object at 0x40701eac> SEGMENT = ()
>>2005/07/07 13:52 IST [HTTPChannel,0,127.0.0.1] IN THE IF
>>2005/07/07 13:52 IST [HTTPChannel,0,127.0.0.1] 127.0.0.1 - -
>>[07/Jul/2005:12:52:11 +0000] "GET /one?id=1 HTTP/1.1" 200 47
>>"http://localhost:8080/" "Mozilla/5.0 (X11; U; Linux i686; en-US;
>>rv:1.7.8) Gecko/20050517 Firefox/1.0.4 (Debian package 1.0.4-2)"
>>2005/07/07 13:52 IST [HTTPChannel,0,127.0.0.1] NAME = favicon.ico
>>2005/07/07 13:52 IST [HTTPChannel,0,127.0.0.1] CHILD = None SEGMENT = ()
>>2005/07/07 13:52 IST [HTTPChannel,0,127.0.0.1] 127.0.0.1 - -
>>[07/Jul/2005:12:52:11 +0000] "GET /favicon.ico HTTP/1.1" 200 684 "-"
>>"Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.8) Gecko/20050517
>>Firefox/1.0.4 (Debian package 1.0.4-2)
>>
>>And when I return to the father, who call to childrenRoot class again,
>>and what is favicon.ico?. I show you the results here.
>>
>>2005/07/07 13:58 IST [HTTPChannel,1,127.0.0.1] NAME = favicon.ico
>>2005/07/07 13:58 IST [HTTPChannel,1,127.0.0.1] CHILD = None SEGMENT = ()
>>2005/07/07 13:58 IST [HTTPChannel,1,127.0.0.1] 127.0.0.1 - -
>>[07/Jul/2005:12:58:34 +0000] "GET /favicon.ico HTTP/1.1" 200 684 "-"
>>"Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.8) Gecko/20050517
>>Firefox/1.0.4 (Debian package 1.0.4-2)"
>>    
>>
>
>favicon.ico is something the browsers request. It's the annoying little
>icon browsers add to tabs and bookmarks. I hate it. See
><http://en.wikipedia.org/wiki/Favicon>.
>
>  
>
>>I would like to know as well if I must to implement all these methods
>>each time that I'm working with children, and what is segments.
>>    
>>
>
>segments is simply a tuple of the remaining URI path segments.
>
>A URL of http://localhost/foo/bar has segments ('foo', 'bar'). Nevow
>tries to turn those segments into child resources until there are no
>more segments left. A typical sequence of events for that URL might be:
>
>1. Nevow asks the root resource to turn 'foo' into a resource. The root
>resource returns a foo resource.
>2. Nevow asks the foo resource to turn 'bar' into a resource. The foo
>resource returns a bar resource.
>3. Nevow seems that there are all segments have been used and asks the
>bar resource to render itself.
>
>However, as you will see below the root resource could consume both
>'foo' and 'bar' and return a bar resource directly.
>
>
>How you choose to traverse the URI depends on what you know and need to
>do ...
>
>If you know the name of a child resource at development time and the
>child resource never changes then use a child_ class attribute:
>
>    class Page(rend.Page):
>        child_css = static.File('/path/to/css')
>
>If you know the name of a child but you need to create it in a special
>way use a child_ method:
>
>    class Page(rend.Page):
>        def child_time(self, ctx):
>            return TimePage(time.now())
>
>If you don't know the name of the resource, i.e. it's a database id or
>something similar, then use childFactory:
>
>    class Page(rend.Page):
>        def childFactory(self, ctx, name):
>            obj = db.getObj(int(name))
>            return ChildPage(obj)
>
>Finally, if you want absolute control, i.e. to consume two URI segments
>in one go, then override locateChild:
>
>    class Page(rend.Page):
>       def locateChild(self, ctx, segments):
>          if segments[:2] == ('foo', 'bar'):
>             return BarPage(), segments[2:]
>          return rend.Page(self, ctx, segments)
>
>Note how that example compares the first 2 segments and consumes both
>'foo' and 'bar' by returning a new BarPage child and the remaining
>segments - segments[2:]. Only locateChild is able to process more than
>one segment at a time.
>
>Personally, I nearly always use child_ and childFactory. I only using
>locateChild for more comlpex URL traversal problems.
>
>  
>
>>Sorry I know that are a lot of question, but I don't have access to
>>the IRC channel and I couldn't understand the information in
>>"inevow.IReource". 
>>    
>>
>
>Hope this explains it well enough now.
>
>Cheers, Matt
>
>  
>