198 lines
5.7 KiB
JavaScript
198 lines
5.7 KiB
JavaScript
/*
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Clean Base MARC example
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Jer Thorp
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3/11/19
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- npm install
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- npm run download-data
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- npm start
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NOTE: You will need to have the URLs you'd like the download script to get listed in data/urls.txt
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NOTE: If the download-data command doesn't work you probably need to install wget:
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OSX: brew install wget
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Windows: http://gnuwin32.sourceforge.net/packages/wget.htm
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This example runs through the Books - (~25m records) - and finds titles with the word 'monkey'.
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It's a purposely simple example to build on. Following examples look at how to expand these concepts.
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*/
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//We're using the xml2object package, which takes XML loaded as text and parses it into a javascript object
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const xml2object = require('xml2object');
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//The filesystem package is used to load the .gz files from the local directory
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const fs = require('fs');
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//The zlib package is used to unzip the .gz files
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const zlib = require('zlib');
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//I like to use this package which provides a clean way to reference to root directory of a node project
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const appRoot = require('app-root-path');
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//Where is the data?
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var dataPath = appRoot + "/data";
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//Which subset of the MARC files were we looking for?
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const filePrefix = "BooksAll";
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//How many of them are there?
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const fileMap = [];
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fileMap["BooksAll"] = 41;
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fileMap["Computer.Files"] = 1;
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fileMap["Maps"] = 1;
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fileMap["Music"] = 1;
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fileMap["Names"] = 37;
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fileMap["Serials"] = 11;
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fileMap["Subjects"] = 2;
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fileMap["Visual.Materials"] = 1;
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//Total number of files to load
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const fileCount = fileMap[filePrefix];
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//Number of files we've already loaded
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//We start at 1 because the MARC files are 1-indexed
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var fileCounter = 1;
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//List to hold objects we want to write to file at the end
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var outList = [];
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//The xml2object package needs us to build a parser object - that will ingest the XML and then
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//trigger functions when the parse is complete.
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const parser = new xml2object([ 'record' ]);
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//------------------XML PARSER ---------------------------------------------------------------------------!!
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//When we construct the parser with an array of which xml elements to look for. In our case, we're
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//interested in the record objects. We also can pass in a reference to the file name.
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function makeParser() {
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//The parser's on method handles events. Here, we'll define what happens when it finishes parsing an object
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parser.on('object', function(name, obj) {
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//Use the parseRecord method to get the Title of the object
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var marcDict = {};
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marcDict["245"] = {"*" :"Title"};
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var record = parseRecord(obj, marcDict);
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//****************************** HERE'S THE PIECE OF CODE THAT ACTUALLY DOES THE THING!!***********
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if (record.Title) {
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var fullTitle = record.Title.join(" ");
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if (fullTitle.toLowerCase().indexOf('monkey') != -1) {
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console.log("FOUND A MONKEY!");
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console.log(record.Title);
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outList.push({title:record.Title})
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}
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}
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});
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//And what happens when it finishes parsing all of the records.
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parser.on('end', function() {
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onParseFinished();
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});
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}
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//------------------MARC PARSE FUNCTION ---------------------------------------------------------------------------!!
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//This function expects an object from xml2obj, and a dictionary object which links
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//the mark tags and subfields to a property name.
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//
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//For example, you could do this:
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// marcDict["260"] = {"c" :"Year"};
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//
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//Which asks the parser to link records with a tag of 260 and a subfield of c to the property Year.
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//
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//You can also use * to say you want ALL subfields of a tag to be stored in a property:
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//
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// marcDict["245"] = {"*" :"Title"};
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function parseRecord(obj, marcDict) {
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record = {};
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for (var i = 0; i < obj.datafield.length; i++) {
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var df = obj.datafield[i];
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//Get the numeric tag
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var tag = df.tag;
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//If we have the tag in our dictionary, write to the JSON object
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//Based on the code (doesn't work for all cases?)
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if (marcDict[tag] && df.subfield) {
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var isAll = marcDict[tag]['*'];
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for (var j = 0; j < df.subfield.length; j++) {
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var code = isAll ? "*":df.subfield[j].code;
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var disp = df.subfield[j]['$t'];
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if (marcDict[tag][code] || isAll) {
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if (!record[marcDict[tag][code]]) {
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record[marcDict[tag][code]] = [];
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}
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record[marcDict[tag][code]].push(disp);
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}
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}
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}
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}
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return(record);
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}
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//------------------FILE LOADING CASCADE ---------------------------------------------------------------------------!!
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//These two functions sequence through the list of MARC records one by one and process them with our
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//xml2object parser
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function loadNextFile() {
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if (fileCounter <= fileCount) {
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//Put a zero in file names under 10
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var n = (fileCounter < 10 ? "0":"") + fileCounter;
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//Construct the URL
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var url = dataPath + "/" + filePrefix + ".2014.part" + n + ".xml.gz";
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//Open up a read stream and unzip it
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var rstream = fs.createReadStream(url);
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var gunzip = zlib.createGunzip();
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rstream // reads from the url we've constructed
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.pipe(gunzip) // uncompresses
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.pipe(parser.saxStream); //Parses into record objects
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fileCounter ++;
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console.log("LOADING FILE : " + url);
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}
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}
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function onParseFinished() {
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//Write every time - useful in very long processes
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writeFile(outList);
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try {
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loadNextFile();
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} catch(err) {
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console.log("ERROR LOADING NEXT FILE: " + fileCounter);
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}
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}
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//------------------JSON WRITER ---------------------------------------------------------------------------!!
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//Writes any JSON object to a file
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function writeFile(json) {
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var json = JSON.stringify(json, null, 2);
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//Write
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console.log("WRITING." + json.length);
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//File prefix is defined on line 26
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fs.writeFile(appRoot + "/out/output_" + filePrefix + ".json", json, 'utf8', function() {
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console.log("Saved JSON.");
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});
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}
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//PULL THE TRIGGER.
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makeParser();
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loadNextFile();
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