Problem using ['@type'] arrays

[ameensol]

graphdb.jsonld.get causes an error when the jsonld document being retrieved has a '@type' property that is an array.

This is the LD document I was attempting to retreive: http://dbpedia.org/data/Ratatat.jsonld

Here is the error (I logged it then threw it):

{ name: 'jsonld.CompactError',
  message: 'Could not expand input before compaction.',
  details: 
   { cause: 
      { name: 'jsonld.SyntaxError',
        message: 'Invalid JSON-LD syntax; "@type" value must a string, an array of strings, or an empty object.',
        details: [Object] } } }

/home/ameen/Desktop/Projects/journalism/jsonld/test.js:239
    if (err) throw err;
                   ^
jsonld.CompactError: Could not expand input before compaction.
    at /home/ameen/Desktop/Projects/journalism/jsonld/node_modules/levelgraph-jsonld/node_modules/jsonld/js/jsonld.js:137:23
    at /home/ameen/Desktop/Projects/journalism/jsonld/node_modules/levelgraph-jsonld/node_modules/jsonld/js/jsonld.js:381:16
    at finished (/home/ameen/Desktop/Projects/journalism/jsonld/node_modules/levelgraph-jsonld/node_modules/jsonld/js/jsonld.js:5838:7)
    at _retrieveContextUrls.retrieve (/home/ameen/Desktop/Projects/journalism/jsonld/node_modules/levelgraph-jsonld/node_modules/jsonld/js/jsonld.js:5844:7)
    at _retrieveContextUrls (/home/ameen/Desktop/Projects/journalism/jsonld/node_modules/levelgraph-jsonld/node_modules/jsonld/js/jsonld.js:5953:3)
    at expand (/home/ameen/Desktop/Projects/journalism/jsonld/node_modules/levelgraph-jsonld/node_modules/jsonld/js/jsonld.js:326:5)
    at /home/ameen/Desktop/Projects/journalism/jsonld/node_modules/levelgraph-jsonld/node_modules/jsonld/js/jsonld.js:304:5
    at process._tickCallback (node.js:415:13)

At first I thought it might be an issue with jsonld, but using jsonld.expand on the document directly produced no errors.

The problem lies with the jsonld document that is being passed to jsonld.expand in levelgraph - more specifically, in how the ['@type'] array is expanded from the triples.

This is the block responsible for expanding the type array from triples.

if (triple.predicate === RDFTYPE) {
  if (acc[triple.subject]['@type']) {
    acc[triple.subject]['@type'] = [acc[triple.subject]['@type']];
    acc[triple.subject]['@type'].push(triple.object);
  } else {
    acc[triple.subject]['@type'] = triple.object;
  }
  cb(null, acc);
}

When this line is removed, it works for me

acc[triple.subject]['@type'] = [acc[triple.subject]['@type']];

Otherwise my ['@type'] array ends up looking something like this:

"@type": [
    [
      [
        [
          [
            [
              [
                [
                  [
                    [
                      [
                        [
                          [
                            [
                              [
                                [
                                  [
                                    [
                                      [
                                        [
                                          [
                                            [
                                              [
                                                [
                                                  "http://dbpedia.org/class/yago/Abstraction100002137",
                                                  "http://dbpedia.org/class/yago/AmericanHouseMusicGroups"
                                                ],
                                                "http://dbpedia.org/class/yago/AmericanPost-rockGroups"
                                              ],
                                              "http://dbpedia.org/class/yago/Communication100033020"
                                            ],
                                            "http://dbpedia.org/class/yago/Couple113743605"
                                          ],
                                          "http://dbpedia.org/class/yago/DefiniteQuantity113576101"
                                        ],
                                        "http://dbpedia.org/class/yago/Device107068844"
                                      ],
                                      "http://dbpedia.org/class/yago/Digit113741022"
                                    ],
                                    "http://dbpedia.org/class/yago/ElectronicMusicDuos"
                                  ],
                                  "http://dbpedia.org/class/yago/ElectronicMusicGroupsFromNewYork"
                                ],
                                "http://dbpedia.org/class/yago/ExpressiveStyle107066659"
                              ],
                              "http://dbpedia.org/class/yago/Group100031264"
                            ],
                            "http://dbpedia.org/class/yago/Integer113728499"
                          ],
                          "http://dbpedia.org/class/yago/Measure100033615"
                        ],
                        "http://dbpedia.org/class/yago/Number113582013"
                      ],
                      "http://dbpedia.org/class/yago/Onomatopoeia107104574"
                    ],
                    "http://dbpedia.org/class/yago/Onomatopoeias"
                  ],
                  "http://dbpedia.org/class/yago/RhetoricalDevice107098193"
                ],
                "http://dbpedia.org/class/yago/Two113743269"
              ],
              "http://dbpedia.org/ontology/Agent"
            ],
            "http://dbpedia.org/ontology/Band"
          ],
          "http://dbpedia.org/ontology/Organisation"
        ],
        "http://schema.org/MusicGroup"
      ],
      "http://schema.org/Organization"
    ],
    "http://www.w3.org/2002/07/owl#Thing"
  ]

[ameensol]

Also this line:

acc[triple.subject]['@type'] = triple.object;

should instantiate the array like this:

acc[triple.subject]['@type'] = [triple.object];

[ameensol]

Hey here is a little test script so you can replicate the error -

var request    = require('request'),
    async      = require('async'),
    jsonld     = require('jsonld');
    levelgraph = require('levelgraph'),
    graphld    = require('levelgraph-jsonld'),
    db         = graphld(levelgraph('db'));

var url = 'http://dbpedia.org/data/Ratatat.jsonld';

request(url, function (err, res, body) {
  data = JSON.parse(body)['@graph'][0];

  db.jsonld.put(data, function (err, obj) {

    // this doesn't work
    db.jsonld.get(data['@id'], {}, function (err, durp) {
      if (err) {
        console.log(err);
        throw err;
      }
      console.log(durp);
    });
  });

  // this works
  // jsonld.expand(data, function (err, obj) {
  //   console.log(obj);
  // });
});

[mcollina]

thanks for finding and fixing this issue!

[ameensol]

Thanks for the awesome library!