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iterator.go
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/
iterator.go
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// Copyright 2014 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 gaedatastore
import (
"fmt"
"github.com/cayleygraph/cayley/graph"
"github.com/cayleygraph/cayley/graph/iterator"
"github.com/cayleygraph/cayley/quad"
"github.com/cayleygraph/cayley/clog"
"google.golang.org/appengine/datastore"
)
type Iterator struct {
uid uint64
size int64
tags graph.Tagger
dir quad.Direction
qs *QuadStore
name string
isAll bool
kind string
hash string
done bool
buffer []string
offset int
last string
result graph.Value
err error
}
var (
bufferSize = 50
)
func NewIterator(qs *QuadStore, k string, d quad.Direction, val graph.Value) *Iterator {
t := val.(*Token)
if t == nil {
clog.Errorf("Token == nil")
}
if t.Kind != nodeKind {
clog.Errorf("Cannot create an iterator from a non-node value")
return &Iterator{done: true}
}
if k != nodeKind && k != quadKind {
clog.Errorf("Cannot create iterator for unknown kind")
return &Iterator{done: true}
}
if qs.context == nil {
clog.Errorf("Cannot create iterator without a valid context")
return &Iterator{done: true}
}
name := quad.StringOf(qs.NameOf(t))
// The number of references to this node is held in the nodes entity
key := qs.createKeyFromToken(t)
foundNode := new(NodeEntry)
err := datastore.Get(qs.context, key, foundNode)
if err != nil && err != datastore.ErrNoSuchEntity {
clog.Errorf("Error: %v", err)
return &Iterator{done: true}
}
size := foundNode.Size
return &Iterator{
uid: iterator.NextUID(),
name: name,
dir: d,
qs: qs,
size: size,
isAll: false,
kind: k,
hash: t.Hash,
done: false,
}
}
func NewAllIterator(qs *QuadStore, kind string) *Iterator {
if kind != nodeKind && kind != quadKind {
clog.Errorf("Cannot create iterator for an unknown kind")
return &Iterator{done: true}
}
if qs.context == nil {
clog.Errorf("Cannot create iterator without a valid context")
return &Iterator{done: true}
}
var size int64
if kind == nodeKind {
size = qs.NodeSize()
} else {
size = qs.Size()
}
return &Iterator{
uid: iterator.NextUID(),
qs: qs,
size: size,
dir: quad.Any,
isAll: true,
kind: kind,
done: false,
}
}
func (it *Iterator) UID() uint64 {
return it.uid
}
func (it *Iterator) Reset() {
it.buffer = nil
it.offset = 0
it.done = false
it.last = ""
it.result = nil
}
func (it *Iterator) Close() error {
it.buffer = nil
it.offset = 0
it.done = true
it.last = ""
it.result = nil
return nil
}
func (it *Iterator) Tagger() *graph.Tagger {
return &it.tags
}
func (it *Iterator) Contains(v graph.Value) bool {
graph.ContainsLogIn(it, v)
if it.isAll {
// The result needs to be set, so when contains is called, the result can be retrieved
it.result = v
return graph.ContainsLogOut(it, v, true)
}
t := v.(*Token)
if t == nil {
clog.Errorf("Could not cast to token")
return graph.ContainsLogOut(it, v, false)
}
if t.Kind == nodeKind {
clog.Errorf("Contains does not work with node values")
return graph.ContainsLogOut(it, v, false)
}
// Contains is for when you want to know that an iterator refers to a quad
var offset int
switch it.dir {
case quad.Subject:
offset = 0
case quad.Predicate:
offset = (quad.HashSize * 2)
case quad.Object:
offset = (quad.HashSize * 2) * 2
case quad.Label:
offset = (quad.HashSize * 2) * 3
}
val := t.Hash[offset : offset+(quad.HashSize*2)]
if val == it.hash {
return graph.ContainsLogOut(it, v, true)
}
return graph.ContainsLogOut(it, v, false)
}
func (it *Iterator) TagResults(dst map[string]graph.Value) {
for _, tag := range it.tags.Tags() {
dst[tag] = it.Result()
}
for tag, value := range it.tags.Fixed() {
dst[tag] = value
}
}
func (it *Iterator) Clone() graph.Iterator {
if it.isAll {
m := NewAllIterator(it.qs, it.kind)
m.tags.CopyFrom(it)
return m
}
// Create a token, the tokens kind is ignored in creation of the iterator
t := &Token{nodeKind, it.hash}
m := NewIterator(it.qs, it.kind, it.dir, t)
m.tags.CopyFrom(it)
return m
}
func (it *Iterator) NextPath() bool {
return false
}
// No subiterators.
func (it *Iterator) SubIterators() []graph.Iterator {
return nil
}
func (it *Iterator) Result() graph.Value {
return it.result
}
func (it *Iterator) Next() bool {
if it.offset+1 < len(it.buffer) {
it.offset++
it.result = &Token{Kind: it.kind, Hash: it.buffer[it.offset]}
return true
}
if it.done {
return false
}
// Reset buffer and offset
it.offset = 0
it.buffer = make([]string, 0, bufferSize)
// Create query
// TODO (panamafrancis) Keys only query?
q := datastore.NewQuery(it.kind).Limit(bufferSize)
if !it.isAll {
// Filter on the direction {subject,objekt...}
q = q.Filter(it.dir.String()+" =", it.name)
}
// Get last cursor position
cursor, err := datastore.DecodeCursor(it.last)
if err == nil {
q = q.Start(cursor)
}
// Buffer the keys of the next 50 matches
t := q.Run(it.qs.context)
for {
// Quirk of the datastore, you cannot pass a nil value to to Next()
// even if you just want the keys
var k *datastore.Key
skip := false
if it.kind == quadKind {
temp := new(QuadEntry)
k, err = t.Next(temp)
// Skip if quad has been deleted
if len(temp.Added) <= len(temp.Deleted) {
skip = true
}
} else {
temp := new(NodeEntry)
k, err = t.Next(temp)
// Skip if node has been deleted
if temp.Size == 0 {
skip = true
}
}
if err == datastore.Done {
it.done = true
break
}
if err != nil {
clog.Errorf("Error fetching next entry %v", err)
it.err = err
return false
}
if !skip {
it.buffer = append(it.buffer, k.StringID())
}
}
// Save cursor position
cursor, err = t.Cursor()
if err == nil {
it.last = cursor.String()
}
// Protect against bad queries
if it.done && len(it.buffer) == 0 {
clog.Warningf("Query did not return any results")
return false
}
// First result
it.result = &Token{Kind: it.kind, Hash: it.buffer[it.offset]}
return true
}
func (it *Iterator) Err() error {
return it.err
}
func (it *Iterator) Size() (int64, bool) {
return it.size, true
}
var gaedatastoreType graph.Type
func init() {
gaedatastoreType = graph.RegisterIterator("gaedatastore")
}
func Type() graph.Type { return gaedatastoreType }
func (it *Iterator) Type() graph.Type {
if it.isAll {
return graph.All
}
return gaedatastoreType
}
func (it *Iterator) Sorted() bool { return false }
func (it *Iterator) Optimize() (graph.Iterator, bool) { return it, false }
func (it *Iterator) Describe() graph.Description {
size, _ := it.Size()
return graph.Description{
UID: it.UID(),
Name: fmt.Sprintf("%s/%s", it.name, it.hash),
Type: it.Type(),
Size: size,
Tags: it.tags.Tags(),
Direction: it.dir,
}
}
// TODO (panamafrancis) calculate costs
func (it *Iterator) Stats() graph.IteratorStats {
size, exact := it.Size()
return graph.IteratorStats{
ContainsCost: 1,
NextCost: 5,
Size: size,
ExactSize: exact,
}
}
var _ graph.Iterator = &Iterator{}