Class: MARC::Writer

Inherits:
Object
  • Object
show all
Defined in:
lib/marc/writer.rb

Overview

However, if you set ‘allow_oversized` to true, then the Writer will write these records out anyway, filling in any binary length/offset slots with all 0’s, if they are not wide enough to hold the true value. While these records are illegal, they can still be read back in using the MARC::ForgivingReader, as well as other platform MARC readers in tolerant mode.

If you set ‘allow_oversized` to false on the Writer, a MARC::Exception will be raised instead, if you try to write an oversized record.

writer = Writer.new(some_path)
writer.allow_oversized = true

Direct Known Subclasses

JSONLWriter

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(file, &blk) ⇒ Writer

the constructor which you must pass a file path or an object that responds to a write message



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# File 'lib/marc/writer.rb', line 31

def initialize(file, &blk)
  if file.instance_of?(String)
    @fh = File.new(file, "w")
  elsif file.respond_to?(:write)
    @fh = file
  else
    raise ArgumentError, "must pass in file name or handle"
  end
  self.allow_oversized = false

  if block_given?
    blk.call(self)
    self.close
  end
end

Instance Attribute Details

#allow_oversized ⇒ Object

Returns the value of attribute allow_oversized.



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# File 'lib/marc/writer.rb', line 26

def allow_oversized
  @allow_oversized
end

Class Method Details

.encode(record, allow_oversized = false) ⇒ Object

a static method that accepts a MARC::Record object and returns the record encoded as MARC21 in transmission format

Second arg allow_oversized, default false, set to true to raise on MARC record that can’t fit into ISO 2709.



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# File 'lib/marc/writer.rb', line 64

def self.encode(record, allow_oversized = false)
  directory = ""
  fields = ""
  offset = 0
  record.each do |field|
    # encode the field
    field_data = ""
    if field.instance_of?(MARC::DataField)
      warn("Warn:  Missing indicator") unless field.indicator1 && field.indicator2
      field_data = (field.indicator1 || " ") + (field.indicator2 || " ")
      field.subfields.each do |s|
        field_data += SUBFIELD_INDICATOR + s.code + s.value
      end
    elsif field.instance_of?(MARC::ControlField)
      field_data = field.value
    end
    field_data += END_OF_FIELD

    # calculate directory entry for the field
    field_length = (field_data.respond_to?(:bytesize) ?
                      field_data.bytesize :
                      field_data.length)
    directory += sprintf("%03s", field.tag) + format_byte_count(field_length, allow_oversized, 4) + format_byte_count(offset, allow_oversized)

    # add field to data for other fields
    fields += field_data

    # update offset for next field
    offset += field_length
  end

  # determine the base (leader + directory)
  base = record.leader + directory + END_OF_FIELD

  # determine complete record
  marc = base + fields + END_OF_RECORD

  # update leader with the byte offest to the end of the directory
  bytesize = base.respond_to?(:bytesize) ? base.bytesize() : base.length
  marc[12..16] = format_byte_count(bytesize, allow_oversized)

  # update the record length
  bytesize = marc.respond_to?(:bytesize) ? marc.bytesize() : marc.length
  marc[0..4] = format_byte_count(bytesize, allow_oversized)

  # store updated leader in the record that was passed in
  record.leader = marc[0..LEADER_LENGTH - 1]

  # return encoded marc
  marc
end

.format_byte_count(number, allow_oversized, num_digits = 5) ⇒ Object

Formats numbers for insertion into marc binary slots. These slots only allow so many digits (and need to be left-padded with spaces to that number of digits). If the number is too big, either an exception will be raised, or we’ll return all 0’s to proper number of digits.

first arg is number, second is boolean whether to allow oversized, third is max digits (default 5)



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# File 'lib/marc/writer.rb', line 124

def self.format_byte_count(number, allow_oversized, num_digits = 5)
  formatted = sprintf("%0#{num_digits}i", number)
  if formatted.length > num_digits
    # uh, oh, we've exceeded our max. Either zero out
    # or raise, depending on settings.
    if allow_oversized
      formatted = sprintf("%0#{num_digits}i", 0)
    else
      raise MARC::Exception.new("Can't write MARC record in binary format, as a length/offset value of #{number} is too long for a #{num_digits}-byte slot.")
    end
  end
  formatted
end

Instance Method Details

#close ⇒ Object

close underlying filehandle



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# File 'lib/marc/writer.rb', line 55

def close
  @fh.close
end

#write(record) ⇒ Object

write a record to the file or handle



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# File 'lib/marc/writer.rb', line 49

def write(record)
  @fh.write(MARC::Writer.encode(record, allow_oversized))
end