Module: Chef::Mixin::DeepMerge

Defined in:
lib/chef/mixin/deep_merge.rb

Overview

Chef::Mixin::DeepMerge

Implements a deep merging algorithm for nested data structures.

Notice:

This code is imported from deep_merge by Steve Midgley. deep_merge is
available under the MIT license from
http://trac.misuse.org/science/wiki/DeepMerge

Defined Under Namespace

Classes: InvalidParameter

Constant Summary collapse

DEFAULT_FIELD_KNOCKOUT_PREFIX = 
'--'

Class Method Summary collapse

Class Method Details

.clear_or_nil(obj) ⇒ Object 



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# File 'lib/chef/mixin/deep_merge.rb', line 211

def self.clear_or_nil(obj)
  if obj.respond_to?(:clear)
    obj.clear
  else
    obj = nil
  end
  obj
end

.deep_merge!(source, dest, options = {}) ⇒ Object

Deep Merge core documentation. deep_merge! method permits merging of arbitrary child elements. The two top level elements must be hashes. These hashes can contain unlimited (to stack limit) levels of child elements. These child elements to not have to be of the same types. Where child elements are of the same type, deep_merge will attempt to merge them together. Where child elements are not of the same type, deep_merge will skip or optionally overwrite the destination element with the contents of the source element at that level. So if you have two hashes like this:

source = {:x => [1,2,3], :y => 2}
dest =   {:x => [4,5,'6'], :y => [7,8,9]}
dest.deep_merge!(source)
Results: {:x => [1,2,3,4,5,'6'], :y => 2}

By default, “deep_merge!” will overwrite any unmergeables and merge everything else. To avoid this, use “deep_merge” (no bang/exclamation mark)

Options:

Options are specified in the last parameter passed, which should be in hash format:
hash.deep_merge!({:x => [1,2]}, {:knockout_prefix => '--'})
:preserve_unmergeables  DEFAULT: false
   Set to true to skip any unmergeable elements from source
:knockout_prefix        DEFAULT: nil
   Set to string value to signify prefix which deletes elements from existing element
:sort_merged_arrays     DEFAULT: false
   Set to true to sort all arrays that are merged together
:unpack_arrays          DEFAULT: nil
   Set to string value to run "Array::join" then "String::split" against all arrays
:merge_debug            DEFAULT: false
   Set to true to get console output of merge process for debugging

Selected Options Details: :knockout_prefix => The purpose of this is to provide a way to remove elements 

from existing Hash by specifying them in a special way in incoming hash
 source = {:x => ['--1', '2']}
 dest   = {:x => ['1', '3']}
 dest.ko_deep_merge!(source)
 Results: {:x => ['2','3']}
Additionally, if the knockout_prefix is passed alone as a string, it will cause
the entire element to be removed:
 source = {:x => '--'}
 dest   = {:x => [1,2,3]}
 dest.ko_deep_merge!(source)
 Results: {:x => ""}

:unpack_arrays => The purpose of this is to permit compound elements to be passed

in as strings and to be converted into discrete array elements
irsource = {:x => ['1,2,3', '4']}
dest   = {:x => ['5','6','7,8']}
dest.deep_merge!(source, {:unpack_arrays => ','})
Results: {:x => ['1','2','3','4','5','6','7','8'}
Why: If receiving data from an HTML form, this makes it easy for a checkbox 
 to pass multiple values from within a single HTML element

There are many tests for this library - and you can learn more about the features and usages of deep_merge! by just browsing the test examples

Raises:



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# File 'lib/chef/mixin/deep_merge.rb', line 93

def self.deep_merge!(source, dest, options = {})
  # turn on this line for stdout debugging text
  merge_debug = options[:merge_debug] || false
  overwrite_unmergeable = !options[:preserve_unmergeables]
  knockout_prefix = options[:knockout_prefix] || nil
  raise InvalidParameter, "knockout_prefix cannot be an empty string in deep_merge!" if knockout_prefix == ""
  raise InvalidParameter, "overwrite_unmergeable must be true if knockout_prefix is specified in deep_merge!" if knockout_prefix && !overwrite_unmergeable
  # if present: we will split and join arrays on this char before merging
  array_split_char = options[:unpack_arrays] || false
  # request that we sort together any arrays when they are merged
  sort_merged_arrays = options[:sort_merged_arrays] || false
  di = options[:debug_indent] || ''
  # do nothing if source is nil
  return dest if source.nil?
  # if dest doesn't exist, then simply copy source to it
  if dest.nil? && overwrite_unmergeable
    dest = source; return dest
  end
     
  puts "#{di}Source class: #{source.class.inspect} :: Dest class: #{dest.class.inspect}" if merge_debug
  if source.kind_of?(Hash)
    puts "#{di}Hashes: #{source.inspect} :: #{dest.inspect}" if merge_debug
    source.each do |src_key, src_value|
      if dest.kind_of?(Hash)
        puts "#{di} looping: #{src_key.inspect} => #{src_value.inspect} :: #{dest.inspect}" if merge_debug
        if dest[src_key]
          puts "#{di} ==>merging: #{src_key.inspect} => #{src_value.inspect} :: #{dest[src_key].inspect}" if merge_debug
          dest[src_key] = deep_merge!(src_value, dest[src_key], options.merge(:debug_indent => di + '  '))
        else # dest[src_key] doesn't exist so we want to create and overwrite it (but we do this via deep_merge!)
          puts "#{di} ==>merging over: #{src_key.inspect} => #{src_value.inspect}" if merge_debug
          # note: we rescue here b/c some classes respond to "dup" but don't implement it (Numeric, TrueClass, FalseClass, NilClass among maybe others)
          begin
            src_dup = src_value.dup # we dup src_value if possible because we're going to merge into it (since dest is empty)
          rescue TypeError
            src_dup = src_value
          end
          dest[src_key] = deep_merge!(src_value, src_dup, options.merge(:debug_indent => di + '  '))
        end
      else # dest isn't a hash, so we overwrite it completely (if permitted)
        if overwrite_unmergeable
          puts "#{di}  overwriting dest: #{src_key.inspect} => #{src_value.inspect} -over->  #{dest.inspect}" if merge_debug
          dest = overwrite_unmergeables(source, dest, options)
        end
      end
    end
  elsif source.kind_of?(Array)
    puts "#{di}Arrays: #{source.inspect} :: #{dest.inspect}" if merge_debug
    # if we are instructed, join/split any source arrays before processing
    if array_split_char
      puts "#{di} split/join on source: #{source.inspect}" if merge_debug
      source = source.join(array_split_char).split(array_split_char)
      if dest.kind_of?(Array)
        dest = dest.join(array_split_char).split(array_split_char)
      end
    end
    # if there's a naked knockout_prefix in source, that means we are to truncate dest
    if source.index(knockout_prefix)
      dest = clear_or_nil(dest); source.delete(knockout_prefix)
    end
    if dest.kind_of?(Array)
      if knockout_prefix
        print "#{di} knocking out: " if merge_debug
        # remove knockout prefix items from both source and dest
        source.delete_if do |ko_item|
          retval = false
          item = ko_item.respond_to?(:gsub) ? ko_item.gsub(%r{^#{knockout_prefix}}, "") : ko_item
          if item != ko_item
            print "#{ko_item} - " if merge_debug
            dest.delete(item)
            dest.delete(ko_item)
            retval = true
          end
          retval
        end
        puts if merge_debug
      end
      puts "#{di} merging arrays: #{source.inspect} :: #{dest.inspect}" if merge_debug
      dest = dest | source
      dest.sort! if sort_merged_arrays
    elsif overwrite_unmergeable
      puts "#{di} overwriting dest: #{source.inspect} -over-> #{dest.inspect}" if merge_debug
      dest = overwrite_unmergeables(source, dest, options)
    end
  else # src_hash is not an array or hash, so we'll have to overwrite dest
    puts "#{di}Others: #{source.inspect} :: #{dest.inspect}" if merge_debug
    dest = overwrite_unmergeables(source, dest, options)
  end
  puts "#{di}Returning #{dest.inspect}" if merge_debug
  dest
end

.merge(first, second) ⇒ Object 



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# File 'lib/chef/mixin/deep_merge.rb', line 29

def self.merge(first, second)
  first  = Mash.new(first)  unless first.kind_of?(Mash)
  second = Mash.new(second) unless second.kind_of?(Mash)

  DeepMerge.deep_merge!(second, first, {:knockout_prefix => "!merge:", :preserve_unmergeables => false})
end

.overwrite_unmergeables(source, dest, options) ⇒ Object

allows deep_merge! to uniformly handle overwriting of unmergeable entities



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# File 'lib/chef/mixin/deep_merge.rb', line 185

def self.overwrite_unmergeables(source, dest, options)
  merge_debug = options[:merge_debug] || false
  overwrite_unmergeable = !options[:preserve_unmergeables]
  knockout_prefix = options[:knockout_prefix] || false
  di = options[:debug_indent] || ''
  if knockout_prefix && overwrite_unmergeable
    if source.kind_of?(String) # remove knockout string from source before overwriting dest
      src_tmp = source.gsub(%r{^#{knockout_prefix}},"")
    elsif source.kind_of?(Array) # remove all knockout elements before overwriting dest
      src_tmp = source.delete_if {|ko_item| ko_item.kind_of?(String) && ko_item.match(%r{^#{knockout_prefix}}) }
    else
      src_tmp = source
    end
    if src_tmp == source # if we didn't find a knockout_prefix then we just overwrite dest
      puts "#{di}#{src_tmp.inspect} -over-> #{dest.inspect}" if merge_debug
      dest = src_tmp
    else # if we do find a knockout_prefix, then we just delete dest
      puts "#{di}\"\" -over-> #{dest.inspect}" if merge_debug
      dest = ""
    end
  elsif overwrite_unmergeable
    dest = source
  end
  dest
end