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timestamps.go
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timestamps.go
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// Copyright 2020 Google LLC
//
// 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 timestamps
import (
"time"
"cloud.google.com/go/datastore"
"github.com/google/uuid"
"google.golang.org/protobuf/types/known/timestamppb"
)
const (
signaturePropertyName = "Signature"
// Precision is the effective precision of timestamps.
// Currently it's 1 microsecond as it's what Datastore supports.
// Datastore: 1 microsecond: https://cloud.google.com/datastore/docs/concepts/entities#date_and_time
Precision = time.Microsecond
)
// Timestamps keeps keeps when each record is created or updated as well as
// a randomly generated UUID to keep consistency under concurrent writes.
// It should be embedded to metadata entities such as Record and Store.
type Timestamps struct {
// CreatedAt is the timestamp of the record creation time
// Automatically set by MetaDB
CreatedAt time.Time `datastore:",noindex"`
// UpdatedAt is the timestamp of the last modification time
// Automatically set and managed by MetaDB
UpdatedAt time.Time `datastore:",noindex"`
// Signature is a UUID that is randomly created each time the record is updated
// Automatically set and managed by MetaDB
Signature uuid.UUID `datastore:"-"`
}
// Assert Timestamps implements the PropertyLoadSaver interface.
var _ datastore.PropertyLoadSaver = new(Timestamps)
// New returns a new Timestamps instance with
// CreatedAt and UpdatedAt set to time.Now() and Signature set to uuid.New().
func New() Timestamps {
now := time.Now().UTC().Truncate(Precision)
return Timestamps{
CreatedAt: now,
UpdatedAt: now,
Signature: uuid.New(),
}
}
// TimeToProto converts time.Time to timestamppb.Timestamp.
// If t is zero, it returns nil.
func TimeToProto(t time.Time) *timestamppb.Timestamp {
if t.IsZero() {
return nil
}
return timestamppb.New(t)
}
// Update updates the UpdatedAt and Signature fields with time.Now() and uuid.New().
func (t *Timestamps) Update() {
t.UpdatedAt = time.Now().UTC().Truncate(Precision)
t.Signature = uuid.New()
}
// Load implements the Datastore PropertyLoadSaver interface and converts Datastore
// properties to corresponding struct fields.
func (t *Timestamps) Load(ps []datastore.Property) error {
sig, ps, err := LoadUUID(ps, signaturePropertyName)
if err != nil {
return err
}
t.Signature = sig
return datastore.LoadStruct(t, ps)
}
// Save implements the Datastore PropertyLoadSaver interface and converts the properties
// field in the struct to separate Datastore properties.
func (t *Timestamps) Save() ([]datastore.Property, error) {
ps, err := datastore.SaveStruct(t)
if err != nil {
return nil, err
}
ps = append(ps, UUIDToDatastoreProperty(signaturePropertyName, t.Signature, true))
return ps, nil
}