transaction.go
// Copyright 2015 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
import "github.com/cayleygraph/cayley/quad"
// Transaction stores a bunch of Deltas to apply together in an atomic step on the database.
type Transaction struct {
// Deltas stores the deltas in the right order
Deltas []Delta
// deltas stores the deltas in a map to avoid duplications
deltas map[Delta]struct{}
}
// NewTransaction initialize a new transaction.
func NewTransaction() *Transaction {
return NewTransactionN(10)
}
// NewTransactionN initialize a new transaction with a predefined capacity.
func NewTransactionN(n int) *Transaction {
return &Transaction{Deltas: make([]Delta, 0, n), deltas: make(map[Delta]struct{}, n)}
}
// AddQuad adds a new quad to the transaction if it is not already present in it.
// If there is a 'remove' delta for that quad, it will remove that delta from
// the transaction instead of actually adding the quad.
func (t *Transaction) AddQuad(q quad.Quad) {
ad, rd := createDeltas(q)
if _, adExists := t.deltas[ad]; !adExists {
if _, rdExists := t.deltas[rd]; rdExists {
t.deleteDelta(rd)
} else {
t.addDelta(ad)
}
}
}
// RemoveQuad adds a quad to remove to the transaction.
// The quad will be removed from the database if it is not present in the
// transaction, otherwise it simply remove it from the transaction.
func (t *Transaction) RemoveQuad(q quad.Quad) {
ad, rd := createDeltas(q)
if _, adExists := t.deltas[ad]; adExists {
t.deleteDelta(ad)
} else {
if _, rdExists := t.deltas[rd]; !rdExists {
t.addDelta(rd)
}
}
}
func createDeltas(q quad.Quad) (ad, rd Delta) {
ad = Delta{
Quad: q,
Action: Add,
}
rd = Delta{
Quad: q,
Action: Delete,
}
return
}
func (t *Transaction) addDelta(d Delta) {
t.Deltas = append(t.Deltas, d)
t.deltas[d] = struct{}{}
}
func (t *Transaction) deleteDelta(d Delta) {
delete(t.deltas, d)
for i, id := range t.Deltas {
if id == d {
t.Deltas = append(t.Deltas[:i], t.Deltas[i+1:]...)
break
}
}
}