LazyXmlModel

Lets you modify xml files using ruby models with an interface similar to ActiveRecord models. It also lazily evaluates the xml file so you do not have to specify a model which covers the entire xml file. This is useful if you only want to modify certain parts of an xml file but do not care about the other contents.

Installation

Install the gem:

gem install lazy_xml_model

And require it from your ruby file:

require 'lazy_xml_model'

Usage

Example XML file company.xml:

<?xml version="1.0" encoding="UTF-8"?>
<company name="SUSE">
  <description type="about">
    <headquarters>Nuremberg</headquarters>
    <website>http://www.suse.com</website>
  </description>
  <trading>yes</trading>
  <employee name="Tanya Erickson">
    <jobtitle>Chief Marketing Synergist</jobtitle>
  </employee>
  <employee name="Rolando Garcia">
    <jobtitle>Human Integration Coordinator</jobtitle>
  </employee>
  <employee name="Xavier Bringham">
    <jobtitle>Regional Markets Executive</jobtitle>
  </employee>
</company>

Ruby models:

class Company
  include LazyXmlModel

  attribute_node :name
  element_node :trading

  has_one :description, class_name: 'Description'
  has_many :employees, class_name: 'Employee'
end

class Description
  include LazyXmlModel

  element_node :headquarters
  element_node :website
end

class Employee
  include LazyXmlModel

  attribute_node :name
  element_node :jobtitle
end

Parsing the xml:

xml_str = File.read('company.xml')
company = Company.parse(xml_str)

Accessing elements & attributes:

company.name
# => 'SUSE'
company.trading
# => 'yes'
company.name = 'openSuse'
company.trading = 'no'

has_one associations:

company.description.headquarters
# => 'Nuremberg'
company.description.destroy # Removes the <description> tag from the xml
company.description
# => nil
company.build_description # Adds a new Description object and <description/> tag
company.description.headquarters = 'Prague' # Sets the value on the new description

has_many associations:

company.employees[0].name
# => 'Tanya Erickson'
company.employees[0].jobtitle
# => 'Chief Marketing Synergist'
company.employees[0].delete # Deletes the employee
company.employees.build # Adds a new blank employee to the collection
company.employees.delete_all

Add a new item to has_many association:

new_employee = Employee.new
new_employee.name = 'Evan Rolfe'
new_employee.jobtitle = 'Junior Xml Parser'
company.employees << new_employee

Outputting the xml:

company.to_xml

Validating the XML input

company = Company.parse('<company name="an invalid company!">')
company.xml_document.errors
# => => [#<Nokogiri::XML::SyntaxError: 1:37: FATAL: Premature end of data in tag company line 1>]

Integrating with ActiveModel

LazyXmlModel plays nicely with ActiveModel so you can have nice things like mass assignment and validations on your xml models.

class Company
  include LazyXmlModel
  include ActiveModel::Model
  include ActiveModel::Validations

  attribute_node :name
  element_node :trading

  has_one :description, class_name: 'Description'
  has_many :employees, class_name: 'Employee'

  validates :name, presence: true
  validates :trading, inclusion: { in: %w(yes no) }
end

Validating the object:

company = Company.new(name: 'My Company', trading: 'i dont know')
company.valid?
# => false
company.errors.messages
# => {:trading=>["is not included in the list"]}

Validating the xml content: Example XML file company.xml:

<?xml version="1.0" encoding="UTF-8"?>
<company>
  <trading>yes</trading>
</company>

xml_str = File.read('company.xml')
company = Company.parse(xml_str)
company.valid?
# => false
company.errors.messages
# => {:name=>["can't be blank"]}

Integrating with rails nested forms

If you include ActiveModel on your models then LazyXmlMapping gives you an _attributes= method on your has_one and has_many associations which means the models can be used with fields_for in the same way that an ActiveRecord model which calls accepts_nested_attributes_for works.

<%= form_for(company) do |f| %>
  <div class="form-group">
    <%= f.label :name %>
    <%= f.text_field :name %>
  </div>

  <div class="form-group">
    <%= f.label :trading %>
    <%= f.text_field :trading %>
  </div>

  <%= f.fields_for :description do |description_fields| %>
    <div class="form-group">
      <%= description_fields.label :headquarters %>
      <%= description_fields.text_field :headquarters %>
    </div>

    <div class="form-group">
      <%= description_fields.label :website %>
      <%= description_fields.text_field :website %>
    </div>
  <% end %>

  <%= f.fields_for :employees, f.object.employees.to_a do |employees_fields| %>
    <hr/>
    <div class="row">
      <b>Employee:</b>
    </div>

    <div class="form-group">
      <%= employees_fields.label :name %>
      <%= employees_fields.text_field :name %>
    </div>

    <div class="form-group">
      <%= employees_fields.label :jobtitle %>
      <%= employees_fields.text_field :jobtitle %>
    </div>

    <div class="form-group">
      <label class="form-check-label">
        <%= employees_fields.check_box :_destroy %>
        Delete?
      </label>
    </div>
  <% end %>

  <%= f.submit 'Save' %>
<% end %>

TODO

Validate associated objects as well as the root object
Handle a collection of elements like: