Class: MARC::Record

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/marc/record.rb

Overview

A class that represents an individual MARC record. Every record is made up of a collection of MARC::DataField objects.

MARC::Record mixes in Enumerable to enable access to constituent DataFields. For example, to return a list of all subject DataFields:

record.find_all {|field| field.tag =~ /^6../}

The accessor ‘fields’ is also an Array of MARC::DataField objects which the client can modify if neccesary.

record.fields.delete(field)

Other accessor attribute: ‘leader’ for record leader as String

High-performance lookup by tag

A frequent use case is looking up fields in a MARC record by tag, such as ‘all the 500 fields’. Certain methods can use a hash keyed by tag name for higher performance lookup by tag. The hash is lazily created on first access – there is some cost of creating the hash, testing shows you get a performance advantage to using the hash-based methods if you are doing at least a dozen lookups.

record.fields("500")  # returns an array
record.each_by_tag("500") {|field| ... }
record.fields(['100', '700'])   # can also use an array in both methods
record.each_by_tag( 600..699 )  # or a range

Freezing for thread-safety and high performance

MARC::Record is not generally safe for sharing between threads. Even if you think you are just acccessing it read-only, you may accidentally trigger a reindex of the by-tag cache (see above).

However, after you are done constructing a Record, you can mark the ‘fields` array as immutable. This makes a Record safe for sharing between threads for read-only use, and also helps you avoid accidentally triggering a reindex, as accidental reindexes can harm by-tag lookup performance. 

record.fields.freeze

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Record

Returns a new instance of Record.



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# File 'lib/marc/record.rb', line 103

def initialize
  @fields = FieldMap.new
  # leader is 24 bytes
  @leader = ' ' * 24
  # leader defaults:
  # http://www.loc.gov/marc/bibliographic/ecbdldrd.html
  @leader[10..11] = '22'
  @leader[20..23] = '4500'
end

Instance Attribute Details

#leader ⇒ Object

the record leader



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# File 'lib/marc/record.rb', line 101

def leader
  @leader
end

Class Method Details

.new_from_hash(h) ⇒ Object 



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# File 'lib/marc/record.rb', line 274

def self.new_from_hash(h)
  r = self.new
  r.leader = h['leader']
  if h['fields']
    h['fields'].each do |position|
      position.each_pair do |tag, field|
        if field.is_a?(Hash)
          f = MARC::DataField.new(tag, field['ind1'], field['ind2'])
          field['subfields'].each do | pos |
            pos.each_pair do |code, value|
              f.append MARC::Subfield.new(code, value)
            end
          end
          r << f
        else
          r << MARC::ControlField.new(tag, field)
        end
      end
    end
  end  
  return r            
end

.new_from_marc(raw, params = {}) ⇒ Object

Factory method for creating a MARC::Record from MARC21 in transmission format.

record = MARC::Record.new_from_marc(marc21)

in cases where you might be working with somewhat flawed MARC data you may want to use the :forgiving parameter which will bypass using field byte offsets and simply look for the end of field byte to figure out the end of fields.

record = MARC::Record.new_from_marc(marc21, :forgiving => true)



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# File 'lib/marc/record.rb', line 201

def self.new_from_marc(raw, params={})
  return MARC::Reader.decode(raw, params)
end

.new_from_marchash(mh) ⇒ Object

Factory method for creating a new MARC::Record from a marchash object

record = MARC::Record->new_from_marchash(mh)



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# File 'lib/marc/record.rb', line 250

def self.new_from_marchash(mh)
  r = self.new()
  r.leader = mh['leader']
  mh['fields'].each do |f|
    if (f.length == 2) 
      r << MARC::ControlField.new(f[0], f[1])
    elsif 
      r << MARC::DataField.new(f[0], f[1], f[2], *f[3])
    end
  end
  return r
end

Instance Method Details

#<<(field) ⇒ Object

alias to append



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# File 'lib/marc/record.rb', line 123

def <<(field)
  append(field)      
end

#==(other) ⇒ Object

For testing if two records can be considered equal.



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# File 'lib/marc/record.rb', line 309

def ==(other)
  return self.to_s == other.to_s
end

#=~(regex) ⇒ Object

Handy for using a record in a regex:

if record =~ /Gravity's Rainbow/ then print "Slothrop" end



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# File 'lib/marc/record.rb', line 317

def =~(regex)
  return self.to_s =~ regex 
end

#[](tag) ⇒ Object

You can lookup fields using this shorthand:

title = record['245']



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# File 'lib/marc/record.rb', line 154

def [](tag)
  return self.find {|f| f.tag == tag}
end

#append(field) ⇒ Object

add a field to the record

record.append(MARC::DataField.new( '100', '2', '0', ['a', 'Fred']))



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# File 'lib/marc/record.rb', line 116

def append(field)
  @fields.push(field)
  @fields.clean = false
end

#each ⇒ Object

each() is here to support iterating and searching since MARC::Record mixes in Enumerable

iterating through the fields in a record:

record.each { |f| print f }

getting the 245

title = record.find {|f| f.tag == '245'}

getting all subjects

subjects = record.find_all {|f| ('600'..'699') === f.tag}



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# File 'lib/marc/record.rb', line 139

def each
  for field in @fields
    yield field
  end
end

#each_by_tag(filter) ⇒ Object

A more convenient way to iterate over each field with a given tag.

The filter argument can be a string, array or range.



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# File 'lib/marc/record.rb', line 147

def each_by_tag(filter)
  @fields.each_by_tag(filter) {|tag| yield tag }
end

#fields(filter = nil) ⇒ Object

Provides a backwards compatible means to access the FieldMap. No argument returns the FieldMap array in entirety. Providing a string, array or range of tags will return an array of fields in the order they appear in the record.



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# File 'lib/marc/record.rb', line 162

def fields(filter=nil)
  unless filter
    # Since we're returning the FieldMap object, which the caller
    # may mutate, we precautionarily mark dirty -- unless it's frozen
    # immutable. 
    @fields.clean = false unless @fields.frozen?
    return @fields 
  end
  @fields.reindex unless @fields.clean
  flds = []
  if filter.is_a?(String) && @fields.tags[filter]
    @fields.tags[filter].each do |idx|
      flds << @fields[idx]
    end
  elsif filter.is_a?(Array) || filter.is_a?(Range)
    @fields.each_by_tag(filter) do |tag|
      flds << tag
    end
  end
  flds
end

#tags ⇒ Object

Returns an array of all of the tags that appear in the record (not necessarily in the order they appear).



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# File 'lib/marc/record.rb', line 185

def tags
  return @fields.tag_list
end

#to_dublin_core ⇒ Object

Handy method for returning a hash mapping this records values to the Dublin Core.

dc = record.to_dublin_core()
print dc['title']



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# File 'lib/marc/record.rb', line 231

def to_dublin_core
  return MARC::DublinCore.map(self)
end

#to_hash ⇒ Object

Returns a (roundtrippable) hash representation for MARC-in-JSON



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# File 'lib/marc/record.rb', line 266

def to_hash
  record_hash = {'leader'=>@leader, 'fields'=>[]}
  @fields.each do |field|
    record_hash['fields'] << field.to_hash
  end
  record_hash
end

#to_marc ⇒ Object

Returns a record in MARC21 transmission format (ANSI Z39.2). Really this is just a wrapper around MARC::MARC21::encode

marc = record.to_marc()



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# File 'lib/marc/record.rb', line 211

def to_marc 
  return MARC::Writer.encode(self)
end

#to_marchash ⇒ Object

Return a marc-hash version of the record



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# File 'lib/marc/record.rb', line 236

def to_marchash
  return {
    'type' => 'marc-hash',
    'version' => [MARCHASH_MAJOR_VERSION, MARCHASH_MINOR_VERSION],
    'leader' => self.leader,
    'fields' => self.map {|f| f.to_marchash}
  }
end

#to_s ⇒ Object

Returns a string version of the record, suitable for printing



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# File 'lib/marc/record.rb', line 298

def to_s
  str = "LEADER #{leader}\n"
  self.each do |field|
    str += field.to_s() + "\n"
  end
  return str
end

#to_xml ⇒ Object

Handy method for returning the MARCXML serialization for a MARC::Record object. You’ll get back a REXML::Document object. Really this is just a wrapper around MARC::XMLWriter::encode

xml_doc = record.to_xml()



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# File 'lib/marc/record.rb', line 221

def to_xml
  return MARC::XMLWriter.encode(self, :include_namespace => true)
end