v6 initial commit, maybe more to follow

test/sparqlEngine/index.js

@@ -0,0 +1,78 @@
+'use strict'
+
+const { BindingBase, HashMapDataset, Graph, PlanBuilder } = require('sparql-engine')
+const level = require('level')
+const levelgraph = require('levelgraph')
+const { Transform } = require('stream')
+
+// An utility class used to convert LevelGraph bindings
+// into a format undestood by sparql-engine
+class FormatterStream extends Transform {
+  constructor () {
+    super({objectMode: true})
+  }
+
+  _transform (item, encoding, callback) {
+    // Transform LevelGraph objects into set of mappings
+    // using BindingBase.fromObject
+    this.push(BindingBase.fromObject(item))
+    callback()
+  }
+}
+
+class LevelRDFGraph extends Graph {
+  constructor (db) {
+    super()
+    this._db = db
+  }
+
+  evalBGP (bgp) {
+    // rewrite variables using levelgraph API
+    bgp = bgp.map(t => {
+      if (t.subject.startsWith('?')) {
+        t.subject = this._db.v(t.subject.substring(1))
+      }
+      if (t.predicate.startsWith('?')) {
+        t.predicate = this._db.v(t.predicate.substring(1))
+      }
+      if (t.object.startsWith('?')) {
+        t.object = this._db.v(t.object.substring(1))
+      }
+      return t
+    })
+    // Transform the Stream returned by LevelGraph into an Stream of Bindings
+    return new FormatterStream(this._db.searchStream(bgp))
+  }
+}
+
+const db = levelgraph(level('testing_db'))
+
+// insert some triples
+var triple1 = { subject: 'http://example.org#a1', predicate: 'http://xmlns.com/foaf/0.1/name', object: '"c"' }
+var triple2 = { subject: 'http://example.org#a2', predicate: 'http://xmlns.com/foaf/0.1/name', object: '"d"' }
+db.put([triple1, triple2], () => {
+  const graph = new LevelRDFGraph(db)
+  const dataset = new HashMapDataset('http://example.org#default', graph)
+
+  const query = `
+    PREFIX foaf: <http://xmlns.com/foaf/0.1/>
+    SELECT ?name
+    WHERE {
+      ?s foaf:name ?name .
+    }`
+
+  // Creates a plan builder for the RDF dataset
+  const builder = new PlanBuilder(dataset)
+
+  // Get an iterator to evaluate the query
+  const iterator = builder.build(query)
+
+  // Read results
+  iterator.subscribe(bindings => {
+    console.log('Find solutions:', bindings.toObject())
+  }, err => {
+    console.error('error', err)
+  }, () => {
+    console.log('Query evaluation complete!')
+  })
+})