[WIP] Implement Resolver iterator

Implement an iterator that takes a slice of nodes and an
associated QuadStore and resolves to their respective
values during iteration.

Resolves #663

CONTRIBUTORS

@@ -11,6 +11,7 @@ Alexander Peters <info@alexanderpeters.de>
 Andrew Dunham <andrew@du.nham.ca>
 Barak Michener <barakmich@google.com> <barak@cayley.io> <me@barakmich.com>
 Bram Leenders <bcleenders@gmail.com>
+Connor Newton <connor@ifthenelse.io>
 Denys Smirnov <denis.smirnov.91@gmail.com>
 Derek Liang <fr.derekliang@gmail.com>
 Jay Graves <jaywgraves@gmail.com>

graph/iterator.go

@@ -272,6 +272,7 @@ const (
 	Regex       = Type("regexp")
 	Count       = Type("count")
 	Recursive   = Type("recursive")
+	Resolver    = Type("resolver")
 )
 
 // String returns a string representation of the Type.

graph/iterator/resolver.go

@@ -0,0 +1,184 @@
+// Copyright 2018 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package iterator
+
+import (
+	"context"
+	"fmt"
+	"github.com/cayleygraph/cayley/graph"
+	"github.com/cayleygraph/cayley/quad"
+)
+
+var _ graph.Iterator = &Resolver{}
+
+// A Resolver iterator consists of it's order, an index (where it is in the,
+// process of iterating) and a store to resolve values from.
+type Resolver struct {
+	qs     graph.QuadStore
+	uid    uint64
+	tags   graph.Tagger
+	order  []quad.Value
+	values map[quad.Value]graph.Value
+	nodes  map[interface{}]quad.Value
+	cached bool
+	index  int
+	err    error
+	result graph.Value
+}
+
+// Creates a new Resolver iterator.
+func NewResolver(qs graph.QuadStore, nodes ...quad.Value) *Resolver {
+	it := &Resolver{
+		uid:    NextUID(),
+		qs:     qs,
+		order:  make([]quad.Value, len(nodes)),
+		// Generally there are going to be no/few duplicates given
+		// so allocate maps large enough to accommodate all
+		values: make(map[quad.Value]graph.Value, len(nodes)),
+		nodes:  make(map[interface{}]quad.Value, len(nodes)),
+	}
+	copy(it.order, nodes)
+	return it
+}
+
+func (it *Resolver) UID() uint64 {
+	return it.uid
+}
+
+func (it *Resolver) Reset() {
+	it.index = 0
+	it.err = nil
+	it.result = nil
+}
+
+func (it *Resolver) Close() error {
+	return nil
+}
+
+func (it *Resolver) Tagger() *graph.Tagger {
+	return &it.tags
+}
+
+func (it *Resolver) TagResults(dst map[string]graph.Value) {
+	it.tags.TagResult(dst, it.Result())
+}
+
+func (it *Resolver) Clone() graph.Iterator {
+	out := NewResolver(it.qs, it.order...)
+	// Nodes and values maps should contain identical data, so
+	// just iterate through one
+	for node, value := range it.values {
+		out.values[node] = value
+		out.nodes[value.Key()] = node
+	}
+	out.tags.CopyFrom(it)
+	return out
+}
+
+func (it *Resolver) String() string {
+	return fmt.Sprintf("Resolver(%v)", it.order)
+}
+
+// Register this iterator as a Resolver iterator.
+func (it *Resolver) Type() graph.Type { return graph.Resolver }
+
+// Resolve nodes to values
+func (it *Resolver) resolve(ctx context.Context) error {
+	values, err := graph.RefsOf(ctx, it.qs, it.order)
+	if err != nil {
+		return err
+	}
+	for index, value := range values {
+		node := it.order[index]
+		it.values[node] = value
+		it.nodes[value.Key()] = node
+	}
+	it.cached = true
+	return nil
+}
+
+// Check if the passed value is equal to one of the order stored in the iterator.
+func (it *Resolver) Contains(ctx context.Context, value graph.Value) bool {
+	graph.ContainsLogIn(it, value)
+	if !it.cached {
+		it.resolve(ctx)
+	}
+	_, ok := it.nodes[value.Key()]
+	return graph.ContainsLogOut(it, value, ok)
+}
+
+// Next advances the iterator.
+func (it *Resolver) Next(ctx context.Context) bool {
+	graph.NextLogIn(it)
+	if it.index == len(it.order) {
+		it.result = nil
+		return graph.NextLogOut(it, false)
+	}
+	if !it.cached {
+		it.resolve(ctx)
+	}
+	node := it.order[it.index]
+	value, ok := it.values[node]
+	if !ok {
+		it.result = nil
+		it.err  = fmt.Errorf("not found: %v", node)
+		return graph.NextLogOut(it, false)
+	}
+	it.result = value
+	it.index++
+	return graph.NextLogOut(it, true)
+}
+
+func (it *Resolver) Err() error {
+	return it.err
+}
+
+func (it *Resolver) Result() graph.Value {
+	return it.result
+}
+
+func (it *Resolver) NextPath(ctx context.Context) bool {
+	return false
+}
+
+func (it *Resolver) SubIterators() []graph.Iterator {
+	return nil
+}
+
+// Returns a Null iterator if it's empty so that upstream iterators can optimize it
+// away, otherwise there is no optimization.
+func (it *Resolver) Optimize() (graph.Iterator, bool) {
+	if len(it.order) == 0 {
+		return NewNull(), true
+	}
+	return it, false
+}
+
+// Size is the number of m stored.
+func (it *Resolver) Size() (int64, bool) {
+	return int64(len(it.order)), true
+}
+
+func (it *Resolver) Stats() graph.IteratorStats {
+	s, exact := it.Size()
+	return graph.IteratorStats{
+		// Lookup cost is size of set
+		ContainsCost: s,
+		// Next is (presumably) O(1) from store
+		NextCost:     1,
+		Size:         s,
+		ExactSize:    exact,
+	}
+}

graph/iterator/resolver_test.go

@@ -0,0 +1,133 @@
+package iterator_test
+
+import (
+	"testing"
+	"context"
+	"github.com/cayleygraph/cayley/quad"
+	"github.com/cayleygraph/cayley/graph"
+	"github.com/cayleygraph/cayley/graph/iterator"
+	"github.com/cayleygraph/cayley/graph/graphmock"
+)
+
+func TestResolverIteratorIterate(t *testing.T) {
+	var ctx context.Context
+	nodes := []quad.Value{
+		quad.String("1"),
+		quad.String("2"),
+		quad.String("3"),
+		quad.String("4"),
+		quad.String("5"),
+		quad.String("3"), // Assert iterator can handle duplicate values
+	}
+	data := make([]quad.Quad, 0, len(nodes))
+	for _, node := range nodes {
+		data = append(data, quad.Make(quad.String("0"), "has", node, nil))
+	}
+	qs := &graphmock.Store{
+		Data: data,
+	}
+	expected := make(map[quad.Value]graph.Value)
+	for _, node := range nodes {
+		expected[node] = qs.ValueOf(node)
+	}
+	it := iterator.NewResolver(qs, nodes...)
+	for _, node := range nodes {
+		if it.Next(ctx) != true {
+			t.Fatal("unexpected end of iterator")
+		}
+		if err := it.Err(); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if value := it.Result(); value != expected[node] {
+			t.Fatalf("unexpected quad value: expected %v, got %v", expected[node], value)
+		}
+	}
+	if it.Next(ctx) != false {
+		t.Fatal("expected end of iterator")
+	}
+	if it.Result() != nil {
+		t.Fatal("expected nil result")
+	}
+}
+
+func TestResolverIteratorNotFoundError(t *testing.T) {
+	var ctx context.Context
+	nodes := []quad.Value{
+		quad.String("1"),
+		quad.String("2"),
+		quad.String("3"),
+		quad.String("4"),
+		quad.String("5"),
+	}
+	data := make([]quad.Quad, 0)
+	skip := 3
+	for i, node := range nodes {
+		// Simulate a missing subject
+		if i == skip {
+			continue
+		}
+		data = append(data, quad.Make(quad.String("0"), "has", node, nil))
+	}
+	qs := &graphmock.Store{
+		Data: data,
+	}
+	count := 0
+	it := iterator.NewResolver(qs, nodes...)
+	for it.Next(ctx) {
+		count++
+	}
+	if count != skip {
+		t.Fatal("unexpected end of iterator")
+	}
+	if it.Err() == nil {
+		t.Fatal("unexpected not found error")
+	}
+	if it.Result() != nil {
+		t.Fatal("expected nil result")
+	}
+}
+
+func TestResolverIteratorContains(t *testing.T) {
+	tests := []struct {
+		name     string
+		nodes    []quad.Value
+		subject  quad.Value
+		contains bool
+	}{
+		{
+			"contains",
+			[]quad.Value{
+				quad.String("1"),
+				quad.String("2"),
+				quad.String("3"),
+			},
+			quad.String("2"),
+			true,
+		},
+		{
+			"not contains",
+			[]quad.Value{
+				quad.String("1"),
+				quad.String("3"),
+			},
+			quad.String("2"),
+			false,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			var ctx context.Context
+			data := make([]quad.Quad, 0, len(test.nodes))
+			for _, node := range test.nodes {
+				data = append(data, quad.Make(quad.String("0"), "has", node, nil))
+			}
+			qs := &graphmock.Store{
+				Data: data,
+			}
+			it := iterator.NewResolver(qs, test.nodes...)
+			if it.Contains(ctx, qs.ValueOf(test.subject)) != test.contains {
+				t.Fatal("unexpected result")
+			}
+		})
+	}
+}