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value_comparison_iterator.go
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/
value_comparison_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 iterator
// "Value Comparison" is a unary operator -- a filter across the values in the
// relevant subiterator.
//
// This is hugely useful for things like label, but value ranges in general
// come up from time to time. At *worst* we're as big as our underlying iterator.
// At best, we're the null iterator.
//
// This is ripe for backend-side optimization. If you can run a value iterator,
// from a sorted set -- some sort of value index, then go for it.
//
// In MQL terms, this is the [{"age>=": 21}] concept.
import (
"strconv"
"github.com/google/cayley/graph"
)
type Operator int
const (
compareLT Operator = iota
compareLTE
compareGT
compareGTE
// Why no Equals? Because that's usually an AndIterator.
)
type Comparison struct {
uid uint64
tags graph.Tagger
subIt graph.Iterator
op Operator
val interface{}
qs graph.QuadStore
result graph.Value
err error
}
func NewComparison(sub graph.Iterator, op Operator, val interface{}, qs graph.QuadStore) *Comparison {
return &Comparison{
uid: NextUID(),
subIt: sub,
op: op,
val: val,
qs: qs,
}
}
func (it *Comparison) UID() uint64 {
return it.uid
}
// Here's the non-boilerplate part of the ValueComparison iterator. Given a value
// and our operator, determine whether or not we meet the requirement.
func (it *Comparison) doComparison(val graph.Value) bool {
//TODO(barakmich): Implement string comparison.
nodeStr := it.qs.NameOf(val)
switch cVal := it.val.(type) {
case int:
cInt := int64(cVal)
intVal, err := strconv.ParseInt(nodeStr, 10, 64)
if err != nil {
return false
}
return RunIntOp(intVal, it.op, cInt)
case int64:
intVal, err := strconv.ParseInt(nodeStr, 10, 64)
if err != nil {
return false
}
return RunIntOp(intVal, it.op, cVal)
default:
return true
}
}
func (it *Comparison) Close() error {
return it.subIt.Close()
}
func RunIntOp(a int64, op Operator, b int64) bool {
switch op {
case compareLT:
return a < b
case compareLTE:
return a <= b
case compareGT:
return a > b
case compareGTE:
return a >= b
default:
panic("Unknown operator type")
}
}
func (it *Comparison) Reset() {
it.subIt.Reset()
}
func (it *Comparison) Tagger() *graph.Tagger {
return &it.tags
}
func (it *Comparison) Clone() graph.Iterator {
out := NewComparison(it.subIt.Clone(), it.op, it.val, it.qs)
out.tags.CopyFrom(it)
return out
}
func (it *Comparison) Next() bool {
for graph.Next(it.subIt) {
val := it.subIt.Result()
if it.doComparison(val) {
it.result = val
return true
}
}
it.err = it.subIt.Err()
return false
}
func (it *Comparison) Err() error {
return it.err
}
// DEPRECATED
func (it *Comparison) ResultTree() *graph.ResultTree {
return graph.NewResultTree(it.Result())
}
func (it *Comparison) Result() graph.Value {
return it.result
}
func (it *Comparison) NextPath() bool {
for {
hasNext := it.subIt.NextPath()
if !hasNext {
it.err = it.subIt.Err()
return false
}
if it.doComparison(it.subIt.Result()) {
break
}
}
it.result = it.subIt.Result()
return true
}
// No subiterators.
func (it *Comparison) SubIterators() []graph.Iterator {
return nil
}
func (it *Comparison) Contains(val graph.Value) bool {
if !it.doComparison(val) {
return false
}
ok := it.subIt.Contains(val)
if !ok {
it.err = it.subIt.Err()
}
return ok
}
// If we failed the check, then the subiterator should not contribute to the result
// set. Otherwise, go ahead and tag it.
func (it *Comparison) 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
}
it.subIt.TagResults(dst)
}
// Registers the value-comparison iterator.
func (it *Comparison) Type() graph.Type { return graph.Comparison }
func (it *Comparison) Describe() graph.Description {
primary := it.subIt.Describe()
return graph.Description{
UID: it.UID(),
Type: it.Type(),
Iterator: &primary,
}
}
// There's nothing to optimize, locally, for a value-comparison iterator.
// Replace the underlying iterator if need be.
// potentially replace it.
func (it *Comparison) Optimize() (graph.Iterator, bool) {
newSub, changed := it.subIt.Optimize()
if changed {
it.subIt.Close()
it.subIt = newSub
}
return it, false
}
// We're only as expensive as our subiterator.
// Again, optimized value comparison iterators should do better.
func (it *Comparison) Stats() graph.IteratorStats {
return it.subIt.Stats()
}
func (it *Comparison) Size() (int64, bool) {
return 0, true
}
var _ graph.Nexter = &Comparison{}