I am trying to add child nodes under a root node .. I tried out with below xml but this doesn't work. I am newbie to Ruby and Nokogiri

builder = Nokogiri::XML::Builder.with(@doc) do |xml|   
  nodes = Nokogiri::XML::NodeSet.new(@doc, [])   
  [].each {|nodes_one_by_one|  
    << nodes_one_by_one.Book  
    << nodes_one_by_one.Pen 
  }      
end

I need to add nodes below a root node like this

<Catalog>
    <Book>abc</Book>
    <Book_Author>Benjamin</Book_author>

That works good for me .. but what i exactly need is to add these Nodes after a specific position in the doc.

<Catalog>
    <!-- 
    <Book>abc</Book>
    <Book_Author>Benjamin</Book_author>
    -->
    <Interface></Interface>
    <Dialog></Dialog>
    <Manifest></Manifest>
</Catalog>

i tried it with at_xpath('//Catlog') but it is adding at the end of the element (as you said)

 <Catalog>
    <Interface></Interface>
    <Dialog></Dialog>
    <Manifest></Manifest>
     <!-- 
      <Book>abc</Book>
      <Book_Author>Benjamin</Book_author>
     -->

book = Nokogiri::XML::Node.new('book', doc)
pen  = Nokogiri::XML::Node.new('pen', doc)     
.
.

Is there anyway to loop using "each" instead of adding one by one .. I tried this way but that doesn't work.

builder = Nokogiri::XML::Builder.with(doc) do |xml|
nodes = Nokogiri::XML::Node.new(doc, [])
[].each {|child_list_element|
child_list_element.Book "value" child_list_element.Pen "value" child_list_element.Diary "value" child_list_element.Pen_stand "value" child_list_element.Pencil "value" . . .
}
end
doc << nodes

The code might be wrong, but i want to do this way. One more this is like .. can i add all the elements as NodeSet instead of Node. Please correct my code.

thanks in advance

Nested OpenStruct doesn't seem to be working fine. I tried with an example below

Catalog collection of Store

require 'ostruct'
require 'nokogiri'

collection = [
OpenStruct.new(:catalogStoreNumber => '657758',
:catalogStoreId => 'CTH6536',
:catalogStoreLocation => 'UnitedStates', 
:catalogOwnerId => 'TYCT11190',
:catalogOwner => 'McGrawHill Pub.',
:catalogList => OpenStruct.new(
    :catalogProductInfo => OpenStruct.new(
    :productType => 'Book',
    :productName => 'The Client',
    :productId => 'CRSUS113246A',
    :productCategory => 'Crime And Suspense',
    :productSubcategory => 'Vintage Books',  
    :productPrice => '45.50 USD',
    :productAuthor => OpenStruct.new(
            :authorFirstName =>'John Grisham',
    :authorMiddleName=> 'Willburt',
    :authorContact => '19876648981')),
:catalogProductInfo => OpenStruct.new(
    :productType => 'Pen',
    :productName => 'Reynolds',
    :productId => 'PRREY546647',
    :productCategory => 'Misc. Stationary',
    :productSubcategory => 'Stationery Items',  
    :productPrice => '3.00 USD',
    :productManufacturer => 'Reynolds Inc.',
    :productAuthor => OpenStruct.new(
        :authorFirstName => 'Ryan Reynolds',
    :authorMiddleName => 'William',
    :authorContact => '16577589898')),
:catalogListType => 'ProductCollection',
:catalogListSource => 'Web'
),
:catalogVerificaitionLog => OpenStruct.new(
    :catalogVerificationStatus => 'Verified',
:catalogVerificationDateTime => '2012-03-12T13:00:15+5:30',
:catalogVerificationId => '64774A',
:catalogVerificationRequestedBy => 'user_121')
)]

i want to access the "productType" of first "catalogProductInfo" and i said "collection.catalogList.catalogProductInfo.productType.content" and I get the below error

"undefined method `productType' for # (NoMethodError)

Does OpenStruct has the support for the Nested OpenStruct I Want to construct an XML in the below format using the OpenStruct and Nokogiri ?

<CatalogOrder>
    <CatalogStoreNumber>657758</CatalogStoreNumber>
    <CatalogStoreId>CTH6536</CatalogStoreId>
    <CatalogStoreLocation>UnitedStates</CatalogStoreLocation>
    <CatalogOwnerId>TYCT11190</CatalogOwnerId>
    <CatalogOwner>McGrawHill Pub.</CatalogOwner>
    <CatalogList>
        <CatalogProductInfo>
        <ProductType>Book</ProductType>
        <ProductName>The Client</ProductName>                          
        <ProductId>CRSUS113246A</ProductId>
        <ProductCategory>Crime And Suspense</ProductCategory>
        <ProductSubCategory>Vintage Books</ProductSubCategory>
        <ProductPrice>45.50 USD</ProductPrice>
        <ProductAuthor>
            <AuthorFirstName>John Grisham</AuthorFirstName>
        <AuthorMiddleName>Willbur</AuthorMiddleName>
        <AuthorContact>19876648981</AuthorContact>
        </ProductAuthor>
    </CatalogProductInfo>
    <CatalogProductInfo>
        <ProductType>Pen</ProductType>
        <ProductName>Reynolds</ProductName>                        
        <ProductId>PRREY546647</ProductId>
        <ProductCategory>Misc. Stationary</ProductCategory>
        <ProductSubCategory>Stationary Items</ProductSubCategory>
        <ProductPrice>3.00 USD</ProductPrice>
        <ProductAuthor>
        <AuthorFirstName>Ryan Reynolds</AuthorFirstName>
        <AuthorMiddleName>William</AuthorMiddleName>
        <AuthorContact>16577589898</AuthorContact>
        </ProductAuthor>
    </CatalogProductInfo>
    <CatalogListType>ProductCollection</CatalogListType>
    <CatalogListSource>Web</CatalogListSource>
</CatalogList>
<CatalogVerificationLog>
    <CatalogVerificationStatus>Verified</CatalogVerificationStatus>
    <CatalogVerificationDateTime>2012-03-12T13:00:15+5:30</CatalogVerificationDateTime>
    <CatalogVerificationId>64774A</CatalogVerificationId>
    <CatalogVerificationRequestedBy>User_121</CatalogVerificationRequestedBy>
</CatalogVerificationLog>

I want to achieve this using Nokogiri and OpenStruct, but I am not sure whether it is possible with OpenStruct, as it lacks Nesting capabilities. Is there any other Way to use JSon to achieve this without any outstanding limitations ? Please correct my earlier code.

If I am understanding you correctly, the following should be roughly what you are looking for:

doc = Nokogiri::XML(original_xml_string) 

catalog = doc.at_css('Catalog') # #at_css will just grab the first node.
                                # use #css if you want to loop through several.
                                # alternatively just use doc.root

book = Nokogiri::XML::Node.new('Book', doc)
book_author = Nokogiri::XML::Node.new('Book_Author', doc)

book.content = 'abc'
book_author.content  = 'benjamin'

catalog << book
catalog << book_author

The << should append the nodes just before the end of the element.

Update

After the updated question and simplified with @Phrogz's suggestions, this should meet your requirements:

require 'nokogiri'

xml = <<'XML'
<Catalog>
  <Interface></Interface>
  <Dialog></Dialog>
  <Manifest></Manifest>
</Catalog>
XML

doc = Nokogiri::XML(xml) 
catalog = doc.root

catalog.first_element_child.before("<Book_Author>abc</Book_Author>")
catalog.first_element_child.before("<Book>benjamin</Book>")

puts doc.to_xml

Update 2

To iterate over a collection, add the nodes dynamically, and using a NodeSet, try the following:

require 'nokogiri'
require 'ostruct'

xml = <<-'XML'
<Catalog>
  <Interface></Interface>
  <Dialog></Dialog>
  <Manifest></Manifest>
</Catalog>
XML

collection = [
  OpenStruct.new(book: '1984', pen: 'George Orwell'),
  OpenStruct.new(book: 'Thinking, Fash and Slow', pen: 'Daniel Kahneman')
]

doc = Nokogiri::XML(xml) 
catalog = doc.root

node_set = Nokogiri::XML::NodeSet.new(doc)
collection.each do |object|
  book = Nokogiri::XML::Node.new('Book', doc)
  book_author = Nokogiri::XML::Node.new('Book_Author', doc)

  book.content = object.book
  book_author.content = object.pen

  node_set << book
  node_set << book_author
end

catalog.first_element_child.before(node_set)

puts doc.to_xml