https://github.com/google/cayley
Tip revision: d858f1f9497628909daa403e2c4756fb69b50522 authored by Iddan Aaronsohn on 30 April 2020, 08:39:42 UTC
Documentation for cayleyexport
Documentation for cayleyexport
Tip revision: d858f1f
session.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 query defines the graph session interface general to all query languages.
package query
import (
"context"
"errors"
"fmt"
"io"
"github.com/cayleygraph/cayley/graph"
)
var ErrParseMore = errors.New("query: more input required")
type ErrUnsupportedCollation struct {
Collation Collation
}
func (e *ErrUnsupportedCollation) Error() string {
return fmt.Sprintf("unsupported collation: %v", e.Collation)
}
// Iterator for query results.
type Iterator interface {
// 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
// Results returns the current result. The type depends on the collation mode of the query.
Result() interface{}
// Err returns any error that was encountered by the Iterator.
Err() error
// Close the iterator and do internal cleanup.
Close() error
}
// Collation of results.
type Collation int
const (
// Raw collates results as maps or arrays of graph.Refs or any other query-native or graph-native data type.
Raw = Collation(iota)
// REPL collates results as strings which will be used in CLI.
REPL = Collation(iota)
// JSON collates results as maps, arrays and values, that can be encoded to JSON.
JSON
// JSONLD collates results as maps, arrays and values compatible with JSON-LD spec.
JSONLD
)
// Options for the query execution.
type Options struct {
Limit int
Collation Collation
}
type Session interface {
// Execute runs the query and returns an iterator over the results.
// Type of results depends on Collation. See Options for details.
Execute(ctx context.Context, query string, opt Options) (Iterator, error)
}
type REPLSession = Session
// ResponseWriter is a subset of http.ResponseWriter
type ResponseWriter interface {
Write([]byte) (int, error)
WriteHeader(int)
}
// Language is a description of query language.
type Language struct {
Name string
Session func(graph.QuadStore) Session
// Custom HTTP handlers
HTTPQuery func(ctx context.Context, qs graph.QuadStore, w ResponseWriter, r io.Reader)
HTTPError func(w ResponseWriter, err error)
}
var languages = make(map[string]Language)
// RegisterLanguage register a new query language.
func RegisterLanguage(lang Language) {
languages[lang.Name] = lang
}
// NewSession creates a new session for specified query language.
// It returns nil if language was not registered.
func NewSession(qs graph.QuadStore, lang string) Session {
if l := languages[lang]; l.Session != nil {
return l.Session(qs)
}
return nil
}
// GetLanguage returns a query language description.
// It returns nil if language was not registered.
func GetLanguage(lang string) *Language {
l, ok := languages[lang]
if ok {
return &l
}
return nil
}
// Languages returns names of registered query languages.
func Languages() []string {
out := make([]string, 0, len(languages))
for name := range languages {
out = append(out, name)
}
return out
}
// Execute runs the query in a given language and returns an iterator over the results.
// Type of results depends on Collation. See Options for details.
func Execute(ctx context.Context, qs graph.QuadStore, lang, query string, opt Options) (Iterator, error) {
l := GetLanguage(lang)
if l == nil {
return nil, fmt.Errorf("unsupported language: %q", lang)
}
sess := l.Session(qs)
return sess.Execute(ctx, query, opt)
}