Barak Michener
3f391a782c
Subcommits: implement iterator and remove ResultTree add Err() to sql remove redundant and less helpful indices, change fillfactor, and use COPY FROM
141 lines
3.6 KiB
Go
141 lines
3.6 KiB
Go
// Copyright 2014 The Cayley Authors. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package quad defines quad and triple handling.
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package quad
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// Defines the struct which makes the QuadStore possible -- the quad.
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//
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// At its heart, it consists of three fields -- Subject, Predicate, and Object.
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// Three IDs that relate to each other. That's all there is to it. The quads
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// are the links in the graph, and the existence of node IDs is defined by the
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// fact that some quad in the graph mentions them.
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//
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// This means that a complete representation of the graph is equivalent to a
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// list of quads. The rest is just indexing for speed.
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//
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// Adding fields to the quad is not to be taken lightly. You'll see I mention
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// label, but don't as yet use it in any backing store. In general, there
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// can be features that can be turned on or off for any store, but I haven't
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// decided how to allow/disallow them yet. Another such example would be to add
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// a forward and reverse index field -- forward being "order the list of
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// objects pointed at by this subject with this predicate" such as first and
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// second children, top billing, what have you.
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//
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// There will never be that much in this file except for the definition, but
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// the consequences are not to be taken lightly. But do suggest cool features!
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import (
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"errors"
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"fmt"
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)
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var (
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ErrInvalid = errors.New("invalid N-Quad")
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ErrIncomplete = errors.New("incomplete N-Quad")
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)
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// Our quad struct, used throughout.
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type Quad struct {
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Subject string `json:"subject"`
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Predicate string `json:"predicate"`
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Object string `json:"object"`
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Label string `json:"label,omitempty"`
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}
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// Direction specifies an edge's type.
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type Direction byte
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// List of the valid directions of a quad.
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const (
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Any Direction = iota
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Subject
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Predicate
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Object
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Label
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)
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var Directions = []Direction{Subject, Predicate, Object, Label}
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func (d Direction) Prefix() byte {
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switch d {
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case Any:
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return 'a'
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case Subject:
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return 's'
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case Predicate:
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return 'p'
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case Label:
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return 'c'
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case Object:
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return 'o'
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default:
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return '\x00'
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}
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}
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func (d Direction) String() string {
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switch d {
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case Any:
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return "any"
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case Subject:
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return "subject"
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case Predicate:
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return "predicate"
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case Label:
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return "label"
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case Object:
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return "object"
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default:
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return fmt.Sprint("illegal direction:", byte(d))
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}
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}
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// Per-field accessor for quads.
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func (q Quad) Get(d Direction) string {
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switch d {
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case Subject:
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return q.Subject
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case Predicate:
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return q.Predicate
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case Label:
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return q.Label
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case Object:
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return q.Object
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default:
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panic(d.String())
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}
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}
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// Pretty-prints a quad.
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func (q Quad) String() string {
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return fmt.Sprintf("%s -- %s -> %s", q.Subject, q.Predicate, q.Object)
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}
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func (q Quad) IsValid() bool {
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return q.Subject != "" && q.Predicate != "" && q.Object != ""
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}
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// Prints a quad in N-Quad format.
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func (q Quad) NQuad() string {
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if q.Label == "" {
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//TODO(barakmich): Proper escaping.
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return fmt.Sprintf("%s %s %s .", q.Subject, q.Predicate, q.Object)
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}
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return fmt.Sprintf("%s %s %s %s .", q.Subject, q.Predicate, q.Object, q.Label)
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}
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type Unmarshaler interface {
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Unmarshal() (Quad, error)
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}
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