A long-lived project that still receives updates
An easy to use, high-performance, flexible and extensible metadata transformation system, focused on library-archives-museums input, and indexing to Solr as output.


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 Project Readme


An easy to use, high-performance, flexible and extensible metadata transformation system, focused on library-archives-museums input, and indexing to Solr as output.

You might use traject to index MARC or XML data for a Solr-based discovery product like Blacklight or VUFind.

Traject can also be generalized to a set of tools for getting structured data from a source, and transforming it to a hash-like object to send to a destination. In addition to sending data to Solr, Traject can produce json or yaml files, tab-delimited files, CSV files, and output suitable for debugging by a human.

Traject is stable, mature software, that is already being used in production by its authors and several other institutions.

Gem Version CI Status


Initially by Jonathan Rochkind (Johns Hopkins Libraries) and Bill Dueber (University of Michigan Libraries).

  • Basic configuration files can be easily written even by non-rubyists, with a few simple directives traject provides. But config files are 'ruby all the way down', so we can provide a gradual slope to more complex needs, with the full power of ruby.
  • Easy to program, easy to read, easy to modify.
  • Fast. Traject by default indexes using multiple threads, on multiple cpu cores, when the underlying ruby implementation (i.e., JRuby) allows it, and can use a separate thread for communication with solr even under MRI. Traject is intended to be usable to process millions of records.
  • Composed of decoupled components, for flexibility and extensibility.f?
  • Designed to support local code and configuration that's maintainable and testable, and can be shared between projects as ruby gems.
  • Easy to split configuration between multiple files, for simple "pick-and-choose" command line options that can combine to deal with any of your local needs.


Traject runs under jruby (9.1.x or higher), MRI ruby (2.3.x or higher), or probably any other ruby platform.

Once you have ruby installed, just $ gem install traject.

If you are processing MARC input, you will probably get significant performance improvements on JRuby. If you are processing Marc-XML (rather than binary Marc21), you should additionally get even more performance improvements by using the traject-marc4j_reader gem on JRuby (see installation instructions there). If performance is a concern, and you are processing MARC, we recommend benchmarking traject on JRuby. (JRuby is not currently recommended for non-MARC XML input.)

Some options for installing a ruby other than your system-provided one are chruby and ruby-install.

Configuration files

traject is configured using configuration files. To get a sense of what they look like, you can take a look at our sample basic MARC configuration file or XML configuration file. You could run traject with that configuration file as: traject -c path/to/demo_config.rb marc_file.marc.

Configuration files are actually just ruby -- so by convention they end in .rb.

We hope you can write basic useful configuration files without much ruby experience, since traject gives you some easy functions to use for common directives. But the full power of ruby is available to you if needed.

rubyist tip: Technically, config files are executed with instance_eval in a Traject::Indexer instance, so the special commands you see are just methods on Traject::Indexer (or mixed into it). But you can call ordinary ruby require in config files, etc., too, to load external functionality. See more at Extending Logic below.

You can keep your settings and indexing rules in one config file, or split them across multiple config files however you like. (Connection details vs indexing? Common things vs environmental specific things?)

There are two main categories of directives in your configuration files: Settings, and Indexing Rules.


Settings are a flat list of key/value pairs, where the keys are always strings and the values usually are too. They look like this in a config file:

# configuration_file.rb
# Note that "#" is a comment, cause it's just ruby

settings do
  # Where to find solr server to write to
  provide "solr.url", ""

  # solr.version doesn't currently do anything, but set it
  # anyway, in the future it will warn you if you have settings
  # that may not work with your version.
  provide "solr.version", "4.3.0"

  # default source type is binary, traject can't guess
  # you have to tell it.
  provide "marc_source.type", "xml"

  # various others...
  provide "solr_writer.commit_on_close", "true"

  # The default writer is the Traject::SolrJsonWriter. In the default MARC mode,
  # the default reader in MARC mode is MarcReader (using ruby-marc).
  # In XML mode, it is the NokogiriReader.

provide will only set the key if it was previously unset, so first setting wins, and command-line comes first of all and overrides everything. You can also use store if you want to force-set: last set wins.

See, docs page on Settings for list of all standardized settings.

Indexing rules: 'to_field'

There are a few methods that can be used to create indexing rules. We will touch on the two most commonly used methods here. More information and technical details are available in Indexing Rules: Macros and Custom Logic

to_field establishes a rule to extract content to a particular named output field. A to_field extraction rule can use built-in 'macros', or, as we'll see later, entirely custom logic.

The built-in macros most commonly used are:

  • In MARC mode, extract_marc, to extract data out of a MARC record according to a tag/subfield specification.
  • In XML mode, extract_xpath. For more on XML use of traject, see the XML guide.

MARC examples: extract_marc

    # Take the value of the first 001 field, and put
    # it in output field 'id', to be indexed in Solr
    # field 'id'
    to_field "id", extract_marc("001")

    to_field "title_t", extract_marc("245aps:130")

    # Can limit to certain indicators with || chars.
    # "*" is a wildcard in indicator spec.  So this is
    # 856 with first indicator '0', subfield u.
    to_field "email_addresses", extract_marc("856|0*|u")

    # Can list tag twice with different field combinations
    # to extract separately
    to_field "isbn", extract_marc("245a:245abcde")

    # For MARC Control ('fixed') fields, you can optionally
    # use square brackets to take a byte offset.
    to_field "language_code", extract_marc("008[35-37]")

extract_marc by default includes all 'alternate script' linked fields corresponding to matched specifications, but you can turn that off, or extract only corresponding 880s.

    to_field "title", extract_marc("245abc", :alternate_script => false)
    to_field "title_vernacular", extract_marc("245abc", :alternate_script => :only)

By default, specifications with multiple subfields (e.g. "240abc") will produce one single string of output per field (for each '240' field in the record), with the concatenation of each matched subfield. Specifications with single subfields (like "020a") will split subfields and produce an output string for each matching subfield (i.e. two output strings for a single '020' with two subfield 'a').

For the syntax and complete possibilities of the specification string argument to extract_marc, see docs at the MarcExtractor class (rdoc).

To see all options for extract_marc, see the extract_marc method documentation.

XML mode, extract_xpath

See our xml guide for more XML examples, but you will usually use extract_xpath.

to_field "title", extract_xpath("//title")

Translation maps

Traject supports translation maps similar to SolrMarc's. There are some translation maps provided by traject, and you can also define your own, in yaml or ruby. Translation maps are especially useful for mapping from MARC codes to user-displayable strings. Translation maps are invokved in a second arg to to_field.

    # "translation_map" will be passed to
    # and the created map used to translate all values
    to_field "language", extract_marc("008[35-37]:041a:041d"), translation_map("marc_language_code")

The argument(s) to translation_map are passed to, see comment docs at TranslationMap for documentation.

The translation_map macro also allows you to specify multiple translation maps, with the latter ones overriding earlier ones:

    to_field "language", extract_marc("008[35-37]:041a:041d"),
                      {"inline_hash" => "even local more overrides"})

Additional transformation macros

TranslationMap use above is just one example of a transformation macro, that transforms output values. Other built-in transformation macros are defined in Traject::Macros::Transformation, and include:

  • default("some value"): provide a default value if no extracted value exists
  • first_only: limit output to a single value, the first one extracted.
  • unique: reduce output values to only unique values
  • strip: remove leading or trailing whitespace
  • prepend("before each value:")
  • append("--after each value")
  • gsub(/regex/, "replacement")
  • split(" "): take values and split them, possibly result in multiple values.
  • transform(proc): transform each existing macro using a proc, kind of like map. eg `to_field "something", extract_xml("//author"), transform( ->(author) { "#{author.last}, #{author.first}" })
  • delete_if(["a", "b"]): remove a value from accumulated values if it is included in the passed in argumet.
    • Can also take a string, proc or regex as an argument. See tests for full functionality.
  • select(proc): selects (keeps) values from accumulated values if proc evaluates to true for specifc value.
    • Can also take a arrays, sets and regex as an argument. See tests for full functionality.

You can add on as many transformation macros as you want, they will be applied to output in order.


to_field "something", extract_xpath("//value"), strip, default("no value"), prepend("Extracted value: ")

Some more MARC-specific utility methods

Other built-in methods that can be used with to_field for MARC specifically include:

Strip punctuation from beginning and end of values using heuristics designed for AACR2 in MARC:

    to_field "title", extract_marc("245abc"), trim_punctuation

the current record serialized back out as MARC, in binary, XML, or json:

    # or :format => "json" for marc-in-json
    # or :format => "binary", by default Base64-encoded for Solr
    # 'binary' field, or, for more like what SolrMarc did, without
    # escaping:
    to_field "marc_record_raw", serialized_marc(:format => "binary", :binary_escape => false, :allow_oversized => true)

text of all fields in a range:

    to_field "text", extract_all_marc_values(:from => "100", :to => "899")

All of these methods are defined at Traject::Macros::Marc21 (rdoc)

More complex canned MARC semantic logic

Some more complex (and opinionated/subjective) algorithms for deriving semantics from Marc are also packaged with Traject, but not available by default. To make them available to your indexing, you just need to use ruby require and extend.

A number of methods are in Traject::Macros::Marc21Semantics (rdoc)

    require 'traject/macros/marc21_semantics'
    extend Traject::Macros::Marc21Semantics

    to_field 'title_sort',        marc_sortable_title
    to_field 'broad_subject',     marc_lcc_to_broad_category
    to_field "geographic_facet",  marc_geo_facet
    # And several more

And, there's a routine for classifying MARC to an internal format/genre/type vocabulary:

    require 'traject/macros/marc_format_classifier'
    extend Traject::Macros::MarcFormats

    to_field 'format_facet',    marc_formats

(Alternately, see the traject_umich_format gem for the often-ridiculously-complex logic used at the University of Michigan.)

Custom logic

The built-in routines are there for your convenience, but if you need something local or custom, you can write ruby logic directly in a configuration file, using a ruby block, which looks like this:

    to_field "id" do |record, accumulator|
       # take the record's 001, prefix it with "bib_",
       # and then add it to the 'accumulator' argument,
       # to send it to the specified output field
       value = record['001']
       value = "bib_#{value}"
       accumulator << value

do |record, accumulator| ... is the definition of a ruby block taking two arguments. The first one passed in will be a source record (eg MARC or XML). The second is an array, you add values to the array to send them to output.

Here's another example that shows how you'd get the record type byte 06 out of a MARC leader, then translate it to a human-readable string with a TranslationMap

    to_field "marc_type" do |record, accumulator|
      leader06 = record.leader.byteslice(6)
      # this translation map doesn't actually exist, but could
      accumulator <<"marc_leader")[ leader06 ]

You can also add a block onto the end of a built-in 'macro', to further customize the output. The accumulator passed to your block will already have values in it from the first step, and you can use ruby methods like map! to modify it:

    to_field "big_title", extract_marc("245abcdefg") do |record, accumulator|
      # put it all in all uppercase, I don't know why.! {|v| v.upcase}

If you find yourself repeating boilerplate code in your custom logic, you can even create your own 'macros' (like extract_marc). extract_marc, translation_map, first_only and other macros are nothing more than methods that return ruby lambda objects of the same format as the blocks you write for custom logic.

In fact, in addition to a literal block on the end, you can pass as many proc objects as you want to transform data.

to_field( "something", extract_xpath("//title"),
          ->(record, acc) { acc << "extra value" },
        ) do |rec, acc|

For tips, gotchas, and a more complete explanation of how this works, see additional documentation page on Indexing Rules: Macros and Custom Logic

each_record and after_processing

In addition to to_field, an each_record method is available, which, like to_field, is executed for every record, but without being tied to a specific output field.

each_record can be used for logging or notifiying, computing intermediate results, or more complex ruby logic.

  each_record do |record|
  each_record do |record, context|
    context.add_output(:some_value, extract_some_value_from_record(record))

For more on each_record, see Indexing Rules: Macros and Custom Logic.

There is also an after_processing method that can be used to register logic that will be called after the entire input has been processed. You can use it for whatever custom ruby code you might want for your app (send an email? Clean up a log file? Trigger a Solr replication?)

after_processing do

Readers and Writers

Traject uses modular 'Writer' classes to take the output hashes from transformation and send them somewhere or do something useful with them.

By default traject uses the Traject::SolrJsonWriter (rdoc) to send to Solr for indexing. Several other writers are also built-in:

You set which writer is being used in settings (provide "writer_class_name", "Traject::DebugWriter"), or with the shortcut command line argument -w Traject::DebugWriter.

The SolrJWriter is packaged separately, and will be useful if you need to index to Solr's older than version 3.2. It requires Jruby.

You can easily write your own Readers and Writers if you'd like, see comments at top of Traject::Indexer. A reader is simply an object that initializes with a ruby IO and traject Settings, and provides an each method. The simplest Writer class initializes with a traject Settings, and provides a put(traject_context) method.

Duplicate, nil, and empty values

A traject settings configuration can be used to control how you want to deal with duplicate values, fields that have no values, and fields that you want to be explicitly set to the value nil.

This allows different writers to get what they expect without having to manually post-process every single field. For example, if you're indexing into Solr you want to ignore empty fields and fields with empty/nil values (which is reflected in the defaults). When working with an RDBMS, though, you may want to send explicit nil values in order to set a column to SQL NULL.

The settings, and their default values, are:

settings do
  provide "allow_duplicate_values",  true  # default is for dups to remain
  provide "allow_nil_values",        false # default is to remove nil values
  provide "allow_empty_fields",      false # default is to ignore empty fields

The defaults should be fine for most uses covered by the included writers.

Each is further explained below.

Allowing/disallowing repeating duplicate values

By default, traject allows the same value to be added to the same field without restriction. You can use the setting allow_duplicate_values = false to disallow duplicate values (i.e., call uniq! on the set of values associated with a given field).

Keeping nil values

traject defaults to throwing away any nils that make it into your accumulator of values. The setting allow_nil_values = true will let nil values pass through.

Dealing with empty fields

Similary, by default traject completely ignores empty fields. You can change this with the setting allow_empty_fields = true, which will result in the output hash having a key for every field mentioned in a to_field statement, whether or not it has any values in it.

Fields that are empty will have a value sent to the writer of an empty array ([]). Writers that need to special-case empty fields should do so in the writer class in question.

The traject command Line

(If you are interested in running traject in an embedded/programmatic context instead of as a standalone command-line batch process, please see docs on Programmatic Use )

The simplest invocation is:

traject -c conf_file.rb marc_file.mrc

By default, and for legacy reasons, the traject command line uses the MarcIndexer, with default marc reader and macros. If you want to use a different indexer for a different file format, use the -i flag: traject -i xml, the NokogiriReader; traject -i basic, the base Traject::Indexer with no format-specific behavior; or traject -i Your::Own::Class.

Traject assumes marc files are in ISO 2709 MARC 'binary' format; it is not currently able to guess other marc format types like XML from filenames or content. If you are reading marc files in another format, you need to tell traject either with the marc_source.type or the command-line shortcut:

traject -c conf.rb -t xml marc_file.xml

You can supply more than one conf file to traject with repeated -c arguments.

traject -c connection_conf.rb -c indexing_conf.rb marc_file.mrc

If you supply a --stdin argument, traject will try to read from stdin. You can only supply one marc file at a time, but we can take advantage of stdin to get around this:

cat some/dir/*.marc | traject -c conf_file.rb --stdin

You can set any setting on the command line with -s key=value. This will over-ride any settings set with provide in conf files.

traject -c conf_file.rb marc_file -s solr.url=http://somehere/solr -s solrj_writer.commit_on_close=true

When using the Traject::MarcIndexer (default), it assumes marc files are in ISO 2709 MARC 'binary' format; it is not currently able to guess other marc format types like XML from filenames or content. If you are reading marc files in another format, you need to tell traject either with the marc_source.type or the command-line shortcut:

traject -c conf.rb -t xml marc_file.xml

To use XML mode instead (with the Traject::NokogiriReader and suitable config files), use the -i flag:

traject -i xml -c xml_suitable_config_file.rb

(You can also pass the full name of a custom indexer class to -i)

There are some built-in command-line option shortcuts for useful settings:

Use --debug-mode to output in a human-readable format, instead of sending to solr. Also turns on debug logging and restricts processing to single-threaded. Useful for debugging or sanity checking.

traject --debug-mode -c conf_file.rb marc_file

Use -u as a shortcut for s solr.url=X

traject -c conf_file.rb -u marc_file.mrc

Run traject -h to see the command line help screen listing all available options.

Also see -I load_path option and suggestions for Bundler use under Extending With Your Own Code.

See also Hints for batch and cronjob use of traject.

A small but complete example

To process a MARC XML file with the data shown in ./examples/marc/tiny.xml you can use save the following configuration as config.rb:

to_field 'title', extract_marc('245a', first: true)

and run Traject as follows:

traject -t xml -c config.rb -w Traject::DebugWriter tiny.xml

-t xml indicates that the file is a MARC XML file. -w Traject::DebugWriter outputs the results to the console (e.g. without saving to Solr).

Extending With Your Own Code

Traject config files are full live ruby files, where you can do anything, including declaring new classes, etc.

However, beyond limited trivial logic, you'll want to organize your code reasonably into separate files, not jam everything into config files.

Traject wants to make sure it makes it convenient for you to do so, whether project-specific logic in files local to the traject project, or in ruby gems that can be shared between projects.

There are standard ruby mechanisms you can use to do this, and traject provides a couple features to make sure this remains convenient with the traject command line.

For more information, see documentation page on Extending With Your Own Code

Expert summary :

  • Traject -I argument command line can be used to list directories to add to the load path, similar to the ruby -I argument. You can then 'require' local project files from the load path.
    • translation map files found on the load path or in a "./translation_maps" subdir on the load path will be found for Traject translation maps.
  • Use Bundler with traject simply by creating a Gemfile with bundler init, and then running command line with bundle exec traject or even BUNDLE_GEMFILE=path/to/Gemfile bundle exec traject


  • Traject XML guide
  • Other traject commands including marcout, and commit
  • Hints for batch and cronjob use of traject.
  • Traject Programmatic Use guide
  • Plugin extensions: Gems that add functionality to traject
    • traject_alephsequential_reader: read MARC files serialized in the AlephSequential format, as output by Ex Libris's Alpeh ILS.
    • traject_horizon: Export MARC records directly from a Horizon ILS rdbms, as serialized MARC or to index into Solr.
    • traject_umich_format: opinionated code and associated macros to extract format (book, audio file, etc.) and types (bibliography, conference report, etc.) from a MARC record. Code mirrors that used by the University of Michigan, and is an alternate approach to that taken by the marc_formats macro in Traject::Macros::MarcFormatClassifier.
    • traject-solrj_writer: a jruby-only writer that uses the solrj .jar to talk directly to solr. Your only option for speaking to a solr version < 3.2, which is when the json handler was added to solr.
    • traject_marc4j_reader: A JRuby-only reader for reading marc records using the Marc4J library, fastest MARC-XML reading on JRuby.
    • traject_sequel_writer A writer for sending to an rdbms via Sequel


Run tests with rake test or just rake. Tests are written using Minitest (please, no rspec). We use the spec-style describe/it to list the tests -- but generally prefer unit-style "assert_*" methods to make actual assertions, for clarity.

To make a pull request, please make a feature branch created from the master branch, not from an existing feature branch. (If you need to do a feature branch dependent on an existing not-yet merged feature branch... discuss this with other developers first!)

Pull requests should come with tests, as well as docs where applicable. Docs can be inline rdoc-style, edits to this README, and/or extra files in ./docs -- as appropriate for what needs to be docs.

Inline api docs Note that our .yardopts file used by to generate online api docs has a --markup markdown specified -- inline class/method docs are in markdown, not rdoc.

Bundler rake tasks included for gem releases: rake release

The standard bundle console command may be useful for getting an irb console with the gem and it's dependencies loaded.

TODO: Possible future improvements

  • Incorporate more inspired by TrajectPlus, possibly including compose for building nested hash output.

  • Incorporate functionality to write multiple output records based on a single input record. Likely will share implementation details with a trajectplus-style compose.

  • Writers for writing to stores other than Solr? ElasticSearch? Maybe.

  • Unicode normalization. Has to normalize to NFKC on way out to index. Except for serialized marc field and other exceptions? Except maybe don't have to, rely on solr analyzer to do it?

    • Should it normalize to NFC on the way in, to make sure translation maps and other string comparisons match properly?

    • Either way, all optional/configurable of course. based on Settings.

  • CommandLine class isn't covered by tests -- it's written using functionality from Indexer and other classes that are well-covered, but the CommandLine itself probably needs some tests -- especially covering error handling, which probably needs a bit more attention and using exceptions instead of exits, etc.

  • Optional built-in jetty stop/start to allow indexing to Solr that wasn't running before. maybe ?