feat: graph traversals

lib/Clownface.js

@@ -421,6 +421,22 @@ class Clownface {
     return this
   }
 
+  from (graph) {
+    const context = this._context.map(context => context.clone({
+      graph: graph === null ? rdf.defaultGraphInstance : graph || undefined
+    }))
+
+    return Clownface.fromContext(context)
+  }
+
+  fromDefaultGraph () {
+    return this.from(rdf.defaultGraphInstance)
+  }
+
+  fromUnionGraph () {
+    return this.from(undefined)
+  }
+
   _toTermArray (predicates, type, languageOrDatatype) {
     return toTermArray(predicates, type, languageOrDatatype, this.factory)
   }

lib/Context.js

@@ -12,8 +12,13 @@ class Context {
     this.term = term(value, undefined, undefined, factory)
   }
 
-  clone ({ dataset = this.dataset, graph = this.graph, value, factory = this.factory, namespace = this.namespace }) {
-    return new Context({ dataset, graph, value, factory, namespace })
+  clone ({ dataset = this.dataset, graph, value, factory = this.factory, namespace = this.namespace }) {
+    let g = graph
+    if (typeof graph === 'undefined') {
+      g = undefined
+    }
+
+    return new Context({ dataset, graph: g, value, factory, namespace })
   }
 
   has (predicate, object) {

test/Clownface/from.js

@@ -0,0 +1,78 @@
+/* global describe, it */
+
+const assert = require('assert')
+const { rdfs } = require('@tpluscode/rdf-ns-builders')
+const clownface = require('../..')
+const rdf = require('../support/factory')
+const ns = require('../support/namespace')
+
+describe('from', () => {
+  it('called with graph changes context to same term in named graph', () => {
+    const term = ns.ex.Foo
+    const dataset = rdf.dataset([
+      rdf.quad(term, rdfs.label, rdf.literal('default graph')),
+      rdf.quad(term, rdfs.label, rdf.literal('named graph'), ns.ex.NamedGraph)
+    ])
+    const pointer = clownface({ dataset, term })
+
+    const movedPointer = pointer.from(ns.ex.NamedGraph)
+
+    assert.deepStrictEqual(movedPointer.out(rdfs.label).value, 'named graph')
+  })
+
+  it('called with undefined changes context to same term across all graphs', () => {
+    const term = ns.ex.Foo
+    const dataset = rdf.dataset([
+      rdf.quad(term, rdfs.label, rdf.literal('default graph')),
+      rdf.quad(term, rdfs.label, rdf.literal('named graph'), ns.ex.NamedGraph)
+    ])
+    const pointer = clownface({ dataset, term, graph: ns.ex.NamedGraph })
+
+    const movedPointer = pointer.from(undefined)
+
+    assert.deepStrictEqual(movedPointer.out(rdfs.label).values.length, 2)
+  })
+
+  it('called with null changes context to same term in default graph', () => {
+    const term = ns.ex.Foo
+    const dataset = rdf.dataset([
+      rdf.quad(term, rdfs.label, rdf.literal('default graph')),
+      rdf.quad(term, rdfs.label, rdf.literal('named graph'), ns.ex.NamedGraph)
+    ])
+    const pointer = clownface({ dataset, term })
+
+    const movedPointer = pointer.from(null)
+
+    assert.deepStrictEqual(movedPointer.out(rdfs.label).value, 'default graph')
+  })
+})
+
+describe('fromDefaultGraph', () => {
+  it('changes context to same term in default graph', () => {
+    const term = ns.ex.Foo
+    const dataset = rdf.dataset([
+      rdf.quad(term, rdfs.label, rdf.literal('default graph')),
+      rdf.quad(term, rdfs.label, rdf.literal('named graph'), ns.ex.NamedGraph)
+    ])
+    const pointer = clownface({ dataset, term })
+
+    const movedPointer = pointer.fromDefaultGraph()
+
+    assert.deepStrictEqual(movedPointer.out(rdfs.label).value, 'default graph')
+  })
+})
+
+describe('fromUnionGraph', () => {
+  it('changes context to same term from all graphs', () => {
+    const term = ns.ex.Foo
+    const dataset = rdf.dataset([
+      rdf.quad(term, rdfs.label, rdf.literal('default graph')),
+      rdf.quad(term, rdfs.label, rdf.literal('named graph'), ns.ex.NamedGraph)
+    ])
+    const pointer = clownface({ dataset, term, graph: ns.ex.NamedGraph })
+
+    const movedPointer = pointer.fromUnionGraph()
+
+    assert.deepStrictEqual(movedPointer.out(rdfs.label).values.length, 2)
+  })
+})