Building XML by enumerating through array & hashes

Question

data =
[ { 'name' => 'category1',
 'subCategory' => [ {'name' => 'subCategory1',
 'product' => [ {'name' => 'prodcutName1',
 'desc' => 'desc1'},
 {'name' => 'prodcutName2',
 'desc' => 'desc2'}]
 } ]
 },
 { 
 #category2 ...and so on 
 }
]

Just recently finished a small project with Ruby. I used the above array of hashes to produce a XML.

I think my solution is quite messy nesting loops and builder tags. Can anyone help me out with a more elegant approach?

builder = Nokogiri::XML::Builder.new { |xml|
data.each { |category| # go through every category in the data array
 xml.category {
 xml.name category['name']
 category['subCategory'].each { |subCategory| # go through each subCategory in the category
 xml.subCategory {
 xml.name subCategory['name']
 subCategory['product'].each { |product| # go though each products and print their data
 xml.name product['name']
 xml.desc product['desc']
 }
 }
 }
 }
}
puts builder.to_xml

• Phrogz: Are you able to change the source data hash to a different format?
• yummisashimi: @Phrogz No, the source needs to stay as it is.

Answer 1

Here's a nice recursive solution, that creates <key>value</key> from 'key'=>'value' entries in your hash. If the value is an array, it instead recurses, using the key name as a wrapper element.

require 'nokogiri'
def process_array(label,array,xml)
 array.each do |hash|
 xml.send(label) do # Create an element named for the label
 hash.each do |key,value|
 if value.is_a?(Array)
 process_array(key,value,xml) # Recurse
 else
 xml.send(key,value) # Create <key>value</key> (using variables)
 end
 end
 end
 end
end
builder = Nokogiri::XML::Builder.new do |xml|
 xml.root do # Wrap everything in one element.
 process_array('category',data,xml) # Start the recursion with a custom name.
 end
end
puts builder.to_xml

When used with this data...

data = [
 { 'name' => 'category1',
 'subCategory' => [
 { 'name' => 'subCategory1',
 'product' => [
 { 'name' => 'productName1',
 'desc' => 'desc1' },
 { 'name' => 'productName2',
 'desc' => 'desc2' } ]
 } ]
 },
 { 'name' => 'category2',
 'subCategory' => [
 { 'name' => 'subCategory2.1',
 'product' => [
 { 'name' => 'productName2.1.1',
 'desc' => 'desc1' },
 { 'name' => 'productName2.1.2',
 'desc' => 'desc2' } ]
 } ]
 },
]

...you get this result:

<?xml version="1.0"?>
<root>
 <category>
 <name>category1</name>
 <subCategory>
 <name>subCategory1</name>
 <product>
 <name>productName1</name>
 <desc>desc1</desc>
 </product>
 <product>
 <name>productName2</name>
 <desc>desc2</desc>
 </product>
 </subCategory>
 </category>
 <category>
 <name>category2</name>
 <subCategory>
 <name>subCategory2.1</name>
 <product>
 <name>productName2.1.1</name>
 <desc>desc1</desc>
 </product>
 <product>
 <name>productName2.1.2</name>
 <desc>desc2</desc>
 </product>
 </subCategory>
 </category>
</root>

---

However, if I had control over the XML schema, I'd do this instead:

require 'nokogiri'
def process_array(label,array,xml)
 array.each do |hash|
 kids,attrs = hash.partition{ |k,v| v.is_a?(Array) }
 xml.send(label,Hash[attrs]) do
 kids.each{ |k,v| process_array(k,v,xml) }
 end
 end
end
builder = Nokogiri::XML::Builder.new do |xml|
 xml.root{ process_array('category',data,xml) }
end
puts builder.to_xml

<?xml version="1.0"?>
<root>
 <category name="category1">
 <subCategory name="subCategory1">
 <product name="productName1" desc="desc1"/>
 <product name="productName2" desc="desc2"/>
 </subCategory>
 </category>
 <category name="category2">
 <subCategory name="subCategory2.1">
 <product name="productName2.1.1" desc="desc1"/>
 <product name="productName2.1.2" desc="desc2"/>
 </subCategory>
 </category>
</root>

...but perhaps you're dealing with some terrible XML schema like PList.

Answer 2

A very clean approach is to use the xml-simple gem. Simply use xml_out with two options:

• RootName to specify the XML root element
• AnonymousTag to provide a tag name for your top-level hash

Other options are documented here.

Code:

require 'xmlsimple'
XmlSimple.xml_out(data, {"RootName" => "categories", "AnonymousTag => "category"})

Output:

<categories>
 <category name="category1">
 <subCategory name="subCategory1">
 <product name="prodcutName1" desc="desc1" />
 <product name="prodcutName2" desc="desc2" />
 </subCategory>
 </category>
 <category></category>
</categories>

Answer 3

Here is a single function to construct XML from a Hash with special handling for attributes and allows a mix of Array and Hash to represent the elements.

You can also begin the Builder outside and call this function after setting up all necessary namespaces.

require 'nokogiri'
def generate_xml(data, parent = false, opt = {})
 return if data.to_s.empty?
 return unless data.is_a?(Hash)
 unless parent
 # assume that if the hash has a single key that it should be the root
 root, data = (data.length == 1) ? data.shift : ["root", data]
 builder = Nokogiri::XML::Builder.new(opt) do |xml|
 xml.send(root) {
 generate_xml(data, xml)
 }
 end
 return builder.to_xml
 end
 data.each { |label, value|
 if value.is_a?(Hash)
 attrs = value.fetch('@attributes', {})
 # also passing 'text' as a key makes nokogiri do the same thing
 text = value.fetch('@text', '') 
 parent.send(label, attrs, text) { 
 value.delete('@attributes')
 value.delete('@text')
 generate_xml(value, parent)
 }
 elsif value.is_a?(Array)
 value.each { |el|
 # lets trick the above into firing so we do not need to rewrite the checks
 el = {label => el}
 generate_xml(el, parent) 
 }
 else
 parent.send(label, value)
 end
 }
end
puts generate_xml(
 {'myroot' => 
 {
 'num' => 99, 
 'title' => 'something witty', 
 'nested' => { 'total' => [99, 98], '@attributes' => {'foo' => 'bar', 'hello' => 'world'}}, 
 'anothernest' => {
 '@attributes' => {'foo' => 'bar', 'hello' => 'world'}, 
 'date' => [
 'today', 
 {'day' => 23, 'month' => 'Dec', 'year' => {'y' => 1999, 'c' => 21}, '@attributes' => {'foo' => 'blhjkldsaf'}}
 ]
 }
 }})
puts puts
puts generate_xml({
 'num' => 99, 
 'title' => 'something witty', 
 'nested' => { 'total' => [99, 98], '@attributes' => {'foo' => 'bar', 'hello' => 'world'}}, 
 'anothernest' => {
 '@attributes' => {'foo' => 'bar', 'hello' => 'world'}, 
 'date' => [
 'today', 
 {'day' => [23,24], 'month' => 'Dec', 'year' => {'y' => 1999, 'c' => 21}, '@attributes' => {'foo' => 'blhjkldsaf'}}
 ]
 }
 })

And the resulting XML output:

<?xml version="1.0"?>
<myroot>
 <num>99</num>
 <title>something witty</title>
 <nested foo="bar" hello="world">
 <total>99</total>
 <total>98</total>
 </nested>
 <anothernest foo="bar" hello="world">
 <date>today</date>
 <date foo="blhjkldsaf">
 <day>23</day>
 <month>Dec</month>
 <year>
 <y>1999</y>
 <c>21</c>
 </year>
 </date>
 </anothernest>
</myroot>
<?xml version="1.0"?>
<root>
 <num>99</num>
 <title>something witty</title>
 <nested foo="bar" hello="world">
 <total>99</total>
 <total>98</total>
 </nested>
 <anothernest foo="bar" hello="world">
 <date>today</date>
 <date foo="blhjkldsaf">
 <day>23</day>
 <day>24</day>
 <month>Dec</month>
 <year>
 <y>1999</y>
 <c>21</c>
 </year>
 </date>
 </anothernest>
</root