Modifiers

Modifiers

Modifiers are methods that provide an easy way to accomplish common tasks to manipulate or retrieve data in specific ways.

The modifiers below can be used in the attribute definition blocks.

Retrieve Value

There are two ways to extract data in order to manipulate it for a specific attribute. Both ways then allow to chain other modifiers to actually make the changes to the data.

Get

The get method retrieves the value of a attribute that has already been processed. (The attributes are always processed from top to bottom).

attribute :subjects, xpath: "//subject"

attribute :something_else do
  get(:subjects)
end

Fetch

The fetch method is provided to have access to the the raw data.

XML based strategy (XML, RSS)

attribute :creator do
  fetch("//author")
end

JSON based strategy (JSON)

attribute :creator do
  fetch("author")
end

Convinience Methods

The following set of methods allow the operator to inspect the values of a particular field. These methods are specially usefull when the operator needs to acomplish conditional

present?

Checks if there is any value at all. Returns true or false.

attribute :category, xpath: "//category" do
  category = get(:category)
  category += ["Images"] if get(:thumbnail_url).present?
  category
end

includes?

Checks if the value provided is included in the set.

attribute :category, xpath: "//category" do
  category = get(:category)
  category += ["News"] if get(:dc_type).includes?("News")
  category
end

to_a

Converts the AttributeValue object to a regular array.

attribute :category, xpath: "//category" do
  get(:category).to_a
end

first

It returns the first value

attribute :category, xpath: "//category" do
  get(:category).first
end

Modify Value

find_with(regexp)

It returns the first element that matches the regular expression.

attribute :identifier do
  get(:identifier).find_with(/IE:\w/)
end

find_all_with(regexp)

It returns all the elements that matches the regular expression.

attribute :identifier do
  get(:identifier).find_all_with(/IE:\w/)
end

find_without(regexp)

It returns the first element that doesn't match the regular expression.

attribute :identifier do
  get(:identifier).find_without(/http/)
end

find_all_without(regexp)

It returns all the elements that don't match the regular expression.

attribute :identifier do
  get(:identifier).find_all_without(/http/)
end

mapping(regexp, substitute_value)

It replaces all the values with the regular expression specified

attribute :enrichment_url do
  get(:identifier).mapping(/.*handle.net(.*)/ => 'https://researchspace.auckland.ac.nz/handle\\1?show=full')
end

The mapping key value pairs can also be repeated to perform multiple substitutions on the same value. For exmaple:

attribute :enrichment_url do
  get(:identifier).mapping(/width=[\d]{1,4}/ => 'width=520', /height=[\d]{1,4}/ => 'height=310')
end

To use captured values from the regular expression use \1 for the first captured value \2 for the second on so on.

select(start, end)

It allows you to select any element or range of elements within an array

Select the first element

attribute :creator do
  get(:creator).select(:first)
end

Select the last element

attribute :creator do
  get(:creator).select(:last)
end

Select from the 2nd element to the last

attribute :creator do
  get(:creator).select(2, :last)
end

Select from the first element to the second to last

attribute :creator do
  get(:creator).select(:first, -2)
end

add(value)

It appends a value to a attribute.

attribute :category, default: ["Newspapers"] do
  get(:category).add("Images") if get(:thumbnail_url).present?
end

compose(value1, value2...)

It joins multiple values from potentially different places.

attribute :subjects do
  compose(get(:tag), "New Zealand", get(:title))
end

to_date

It tries to parse the values into real dates.

attribute :date do
  get(:display_date).to_date
end

split(split_value)

It will try and split all values by the value specified.

attribute :subject do
  get(:subject).split(",")
end

The above code will convert a string in the following format "dogs, cats, puma" to ["dogs", " cats", " puma"]

attribute :subject do
  get(:subject).split(/\d/)
end

The splitter can also split based on a regular expression.

truncate(length, omission="...")

It will truncate all values to the specified length. The omission defaults to three dots "...", but a different string can be specified.

attribute :description do
  get(:description).truncate(300)
end

It will truncate the string to 300 charachters.

attribute :description do
  get(:description).truncate(10, "")
end

It will truncate the string to 10 characters and it won't add anything at the end of the string.

downcase

It will downcase all the values

attribute :identifier do
  get(:identifier).downcase
end