https://github.com/google/cayley
Tip revision: cdaa0999d766d9229389a3eab515e4226ec925bc authored by Denys Smirnov on 17 October 2019, 12:12:48 UTC
linkedql: add registration for query steps
linkedql: add registration for query steps
Tip revision: cdaa099
iterator.go
// 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 graph
// Define the general iterator interface.
import (
"context"
"github.com/cayleygraph/quad"
)
// TODO(barakmich): Linkage is general enough that there are places we take
//the combined arguments `quad.Direction, graph.Ref` that it may be worth
//converting these into Linkages. If nothing else, future indexed iterators may
//benefit from the shared representation
// Linkage is a union type representing a set of values established for a given
// quad direction.
type Linkage struct {
Dir quad.Direction
Value Ref
}
// TODO(barakmich): Helper functions as needed, eg, ValuesForDirection(quad.Direction) []Ref
// TaggerBase is a base interface for Tagger and TaggerShape.
type TaggerBase interface {
Tags() []string
FixedTags() map[string]Ref
AddTags(tag ...string)
AddFixedTag(tag string, value Ref)
}
// IteratorBase is a set of common methods for Scanner and Index iterators.
type IteratorBase interface {
// String returns a short textual representation of an iterator.
String() string
// Fills a tag-to-result-value map.
TagResults(map[string]Ref)
// Returns the current result.
Result() Ref
// These methods are the heart and soul of the iterator, as they constitute
// the iteration interface.
//
// To get the full results of iteration, do the following:
//
// for graph.Next(it) {
// val := it.Result()
// ... do things with val.
// for it.NextPath() {
// ... find other paths to iterate
// }
// }
//
// All of them should set iterator.result to be the last returned value, to
// make results work.
//
// NextPath() advances iterators that may have more than one valid result,
// from the bottom up.
NextPath(ctx context.Context) bool
// Err returns any error that was encountered by the Iterator.
Err() error
// TODO: make a requirement that Err should return ErrClosed after Close is called
// Close the iterator and do internal cleanup.
Close() error
}
// Scanner is an iterator that lists all results sequentially, but not necessarily in a sorted order.
type Scanner interface {
IteratorBase
// Next advances the iterator to the next value, which will then be available through
// the Result method. It returns false if no further advancement is possible, or if an
// error was encountered during iteration. Err should be consulted to distinguish
// between the two cases.
Next(ctx context.Context) bool
}
// Index is an index lookup iterator. It allows to check if an index contains a specific value.
type Index interface {
IteratorBase
// Contains returns whether the value is within the set held by the iterator.
//
// It will set Result to the matching subtree. TagResults can be used to collect values from tree branches.
Contains(ctx context.Context, v Ref) bool
}
// Tagger is an interface for iterators that can tag values. Tags are returned as a part of TagResults call.
type TaggerShape interface {
IteratorShape
TaggerBase
CopyFromTagger(st TaggerBase)
}
type IteratorCosts struct {
ContainsCost int64
NextCost int64
Size Size
}
// Shape is an iterator shape, similar to a query plan. But the plan is not specific in this
// case - it is used to reorder query branches, and the decide what branches will be scanned
// and what branches will lookup values (hopefully from the index, but not necessarily).
type IteratorShape interface {
// TODO(dennwc): merge with shape.Shape
// String returns a short textual representation of an iterator.
String() string
// Iterate starts this iterator in scanning mode. Resulting iterator will list all
// results sequentially, but not necessary in the sorted order. Caller must close
// the iterator.
Iterate() Scanner
// Lookup starts this iterator in an index lookup mode. Depending on the iterator type,
// this may still involve database scans. Resulting iterator allows to check an index
// contains a specified value. Caller must close the iterator.
Lookup() Index
// These methods relate to choosing the right iterator, or optimizing an
// iterator tree
//
// Stats() returns the relative costs of calling the iteration methods for
// this iterator, as well as the size. Roughly, it will take NextCost * Size
// "cost units" to get everything out of the iterator. This is a wibbly-wobbly
// thing, and not exact, but a useful heuristic.
Stats(ctx context.Context) (IteratorCosts, error)
// Optimizes an iterator. Can replace the iterator, or merely move things
// around internally. if it chooses to replace it with a better iterator,
// returns (the new iterator, true), if not, it returns (self, false).
Optimize(ctx context.Context) (IteratorShape, bool)
// Return a slice of the subiterators for this iterator.
SubIterators() []IteratorShape
}
// ApplyMorphism is a curried function that can generates a new iterator based on some prior iterator.
type ApplyMorphism func(QuadStore, IteratorShape) IteratorShape
// Height is a convienence function to measure the height of an iterator tree.
func Height(it IteratorShape, filter func(IteratorShape) bool) int {
if filter != nil && !filter(it) {
return 1
}
subs := it.SubIterators()
maxDepth := 0
for _, sub := range subs {
h := Height(sub, filter)
if h > maxDepth {
maxDepth = h
}
}
return maxDepth + 1
}
type IteratorStats struct {
ContainsCost int64
NextCost int64
Size int64
ExactSize bool
Next int64
Contains int64
ContainsNext int64
}