Class: Traject::TranslationMap

Inherits:
Object
  • Object
show all
Defined in:
lib/traject/translation_map.rb

Overview

A TranslationMap is basically just something that has a hash-like #[] method to map from input strings to output strings:

translation_map["some_input"] #=> some_output

Input is assumed to always be string, output is either string or array of strings.

What makes it more useful than a stunted hash is it's ability to load the hash definitions from configuration files, either pure ruby, yaml, or java .properties file (not all .properties features may be supported, we use dot-properties gem for reading)

traject's extract_marc macro allows you to specify a :translation_map=>filename argument that will automatically find and use a translation map on the resulting data:

extract_marc("040a", :translation_map => "languages")

Or you can always create one yourself and use it how you like:

map = TranslationMap.new("languages")

In either case, TranslationMap will look for a file named, in that example, languages.rb or languages.yaml or languages.properties, somewhere in the ruby $LOAD_PATH in a /translation_maps subdir.

  • Also looks for "/translation_maps" subdir in load paths, so for instance you can have a gem that keeps translation maps in ./lib/translation_maps, and it Just Works.

  • Note you do NOT supply the .rb, .yaml, or .properties suffix yourself, it'll use whichever it finds (allows calling code to not care which is used).

Ruby files just need to have their last line eval to a hash. They file will be run through eval, don't do it with untrusted content (naturally)

You can also pass in a Hash for consistency to TranslationMap.new, although I don't know why you'd want to.

Special default handling

The key "default" in the hash is treated specially. If set to a string, that string will be returned by the TranslationMap for any input not otherwise included. If set to the special string "passthrough", then for input not mapped, the original input string will be returned.

This is most useful for YAML definition files, if you are using an actual ruby hash, you could just set the hash to do what you want using Hash#default_proc etc.

Or, when calling TranslationMap.new(), you can pass in options over-riding special key too:

TranslationMap.new("something", :default => "foo") TranslationMap.new("something", :default => :passthrough)

Output: String or array of strings

The output can be a string or an array of strings, or nil. It should not be anything else. When used with the #translate_array! method, one string can be replaced by multiple values (array of strings) or removed (nil)

There's no way to specify multiple return values in a .properties, use .yaml or .rb for that.

Caching

Lookup and loading of configuration files will be cached, for efficiency. You can reset with TranslationMap.reset_cache!

YAML example:

key: value
key2: value2 multiple words fine
key2b: "Although you can use quotes if you want: Or need."
key3:
  - array
  - of
  - values look like this

Alternatives

Traject::TranslationMap provides an easy way to deal with the most common translation case: simple key-value stores with optional default values.

If you need more complex translation, you can simply use #map! or its kin to work on the accumulator in a block

# get a lousy language detection of any vernacular title
require 'whatlanguage'
wl = WhatLanguage.new(:all)
to_field 'vernacular_langauge', extract_marc('245', :alternate_script=>:only) do |rec, acc|
  # accumulator is already filled with the values of any 880s that reference a 245 because
  # of the call to #extract_marc
  acc.map! {|x| wl.language(x) }
  acc.uniq!
end

Within the block, you may also be interested in using:

  • a case-insentive hash, perhaps like this one
  • a MatchMap, which implements pattern-matching logic similar to solrmarc's pattern files

Defined Under Namespace

Classes: Cache, NotFound

Class Attribute Summary collapse

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(defn, options = {}) ⇒ TranslationMap

Returns a new instance of TranslationMap.



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# File 'lib/traject/translation_map.rb', line 169

def initialize(defn, options = {})
  if defn.kind_of? Hash
    @hash = defn
  elsif defn.kind_of? self.class
    @hash = defn.to_hash
    @default = defn.default
  else
    @hash = self.class.cache.lookup(defn)
    raise NotFound.new(defn) if @hash.nil?
  end

  if options[:default]
    @default = options[:default]
  elsif @hash.has_key? "__default__"
    @default = @hash["__default__"]
  end
end

Class Attribute Details

.cache ⇒ Object

Returns the value of attribute cache.



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# File 'lib/traject/translation_map.rb', line 161

def cache
  @cache
end

Instance Attribute Details

#default ⇒ Object (readonly)

Returns the value of attribute default.



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# File 'lib/traject/translation_map.rb', line 158

def default
  @default
end

#hash ⇒ Object (readonly)

Returns the value of attribute hash.



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# File 'lib/traject/translation_map.rb', line 157

def hash
  @hash
end

Class Method Details

.reset_cache! ⇒ Object 



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# File 'lib/traject/translation_map.rb', line 162

def reset_cache!
  cache.reset_cache!
end

Instance Method Details

#[](key) ⇒ Object Also known as: map 



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# File 'lib/traject/translation_map.rb', line 187

def [](key)
  if self.default && (! @hash.has_key?(key))
    if self.default == "__passthrough__"
      return key
    else
      return self.default
    end
  end

  @hash[key]
end

#merge(other_map) ⇒ Object

Return a new TranslationMap that results from merging argument on top of self. Can be useful for taking an existing translation map, but merging a few overrides on top.

merged_map = TranslationMap.new(something).merge TranslationMap.new(else)
#...
merged_map.translate_array(something) # etc

If a default is set in the second map, it will merge over the first too.

You can also pass in a plain hash as an arg, instead of an existing TranslationMap:

TranslationMap.new(something).merge("overridden_key" => "value", "a" => "")



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# File 'lib/traject/translation_map.rb', line 245

def merge(other_map)
  default = other_map.default || self.default
  TranslationMap.new(self.to_hash.merge(other_map.to_hash), :default => default)
end

#to_hash ⇒ Object

Returns a dup of internal hash, dup so you can modify it if you like.



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# File 'lib/traject/translation_map.rb', line 202

def to_hash
  dup = @hash.dup
  dup.delete("__default__")
  dup
end

#translate_array(array) ⇒ Object

Run every element of an array through this translation map, return the resulting array. If translation map returns nil, original element will be missing from output.

If an input maps to an array, each element of the array will be flattened into the output.

If an input maps to nil, it will cause the input element to be removed entirely.



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# File 'lib/traject/translation_map.rb', line 217

def translate_array(array)
  array.each_with_object([]) do |input_element, output_array|
    output_element = self.map(input_element)
    if output_element.kind_of? Array
      output_array.concat output_element
    elsif ! output_element.nil?
      output_array << output_element
    end
  end
end

#translate_array!(array) ⇒ Object 



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# File 'lib/traject/translation_map.rb', line 228

def translate_array!(array)
  array.replace( self.translate_array(array))
end