pkg/db/model/non_persisted_revision.go - voltha-lib-go - Gitiles

 /*
  * Copyright 2018-present Open Networking Foundation

  * 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 model

 import (
 	"bytes"
 	"context"
 	"crypto/md5"
 	"fmt"
 	"github.com/golang/protobuf/proto"
 	"github.com/opencord/voltha-lib-go/pkg/db/kvstore"
 	"github.com/opencord/voltha-lib-go/pkg/log"
 	"reflect"
 	"sort"
 	"strings"
 	"sync"
 	"time"
 )

 // TODO: Cache logic will have to be revisited to cleanup unused entries in memory (disabled for now)
 //
 type revCacheSingleton struct {
 	sync.RWMutex
 	Cache sync.Map
 }

 func (s *revCacheSingleton) Get(path string) (interface{}, bool) {
 	return s.Cache.Load(path)
 }
 func (s *revCacheSingleton) Set(path string, value interface{}) {
 	s.Cache.Store(path, value)
 }
 func (s *revCacheSingleton) Delete(path string) {
 	s.Cache.Delete(path)
 }

 var revCacheInstance *revCacheSingleton
 var revCacheOnce sync.Once

 func GetRevCache() *revCacheSingleton {
 	revCacheOnce.Do(func() {
 		revCacheInstance = &revCacheSingleton{Cache: sync.Map{}}
 	})
 	return revCacheInstance
 }

 type NonPersistedRevision struct {
 	mutex        sync.RWMutex
 	Root         *root
 	Config       *DataRevision
 	childrenLock sync.RWMutex
 	Children     map[string][]Revision
 	Hash         string
 	Branch       *Branch
 	WeakRef      string
 	Name         string
 	lastUpdate   time.Time
 }

 func NewNonPersistedRevision(root *root, branch *Branch, data interface{}, children map[string][]Revision) Revision {
 	r := &NonPersistedRevision{}
 	r.Root = root
 	r.Branch = branch
 	r.Config = NewDataRevision(root, data)
 	r.Children = children
 	r.Hash = r.hashContent()
 	return r
 }

 func (npr *NonPersistedRevision) SetConfig(config *DataRevision) {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()
 	npr.Config = config
 }

 func (npr *NonPersistedRevision) GetConfig() *DataRevision {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()
 	return npr.Config
 }

 func (npr *NonPersistedRevision) SetAllChildren(children map[string][]Revision) {
 	npr.childrenLock.Lock()
 	defer npr.childrenLock.Unlock()
 	npr.Children = make(map[string][]Revision)

 	for key, value := range children {
 		npr.Children[key] = make([]Revision, len(value))
 		copy(npr.Children[key], value)
 	}
 }

 func (npr *NonPersistedRevision) SetChildren(name string, children []Revision) {
 	npr.childrenLock.Lock()
 	defer npr.childrenLock.Unlock()

 	npr.Children[name] = make([]Revision, len(children))
 	copy(npr.Children[name], children)
 }

 func (npr *NonPersistedRevision) GetAllChildren() map[string][]Revision {
 	npr.childrenLock.Lock()
 	defer npr.childrenLock.Unlock()

 	return npr.Children
 }

 func (npr *NonPersistedRevision) GetChildren(name string) []Revision {
 	npr.childrenLock.Lock()
 	defer npr.childrenLock.Unlock()

 	if _, exists := npr.Children[name]; exists {
 		return npr.Children[name]
 	}
 	return nil
 }

 func (npr *NonPersistedRevision) SetHash(hash string) {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()
 	npr.Hash = hash
 }

 func (npr *NonPersistedRevision) GetHash() string {
 	//npr.mutex.Lock()
 	//defer npr.mutex.Unlock()
 	return npr.Hash
 }

 func (npr *NonPersistedRevision) ClearHash() {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()
 	npr.Hash = ""
 }

 func (npr *NonPersistedRevision) GetName() string {
 	//npr.mutex.Lock()
 	//defer npr.mutex.Unlock()
 	return npr.Name
 }

 func (npr *NonPersistedRevision) SetName(name string) {
 	//npr.mutex.Lock()
 	//defer npr.mutex.Unlock()
 	npr.Name = name
 }
 func (npr *NonPersistedRevision) SetBranch(branch *Branch) {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()
 	npr.Branch = branch
 }

 func (npr *NonPersistedRevision) GetBranch() *Branch {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()
 	return npr.Branch
 }

 func (npr *NonPersistedRevision) GetData() interface{} {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()
 	if npr.Config == nil {
 		return nil
 	}
 	return npr.Config.Data
 }

 func (npr *NonPersistedRevision) GetNode() *node {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()
 	return npr.Branch.Node
 }

 func (npr *NonPersistedRevision) Finalize(skipOnExist bool) {
 	npr.Hash = npr.hashContent()
 }

 // hashContent generates a hash string based on the contents of the revision.
 // The string should be unique to avoid conflicts with other revisions
 func (npr *NonPersistedRevision) hashContent() string {
 	var buffer bytes.Buffer
 	var childrenKeys []string

 	if npr.Config != nil {
 		buffer.WriteString(npr.Config.Hash)
 	}

 	if npr.Name != "" {
 		buffer.WriteString(npr.Name)
 	}

 	for key := range npr.Children {
 		childrenKeys = append(childrenKeys, key)
 	}

 	sort.Strings(childrenKeys)

 	if len(npr.Children) > 0 {
 		// Loop through sorted Children keys
 		for _, key := range childrenKeys {
 			for _, child := range npr.Children[key] {
 				if child != nil && child.GetHash() != "" {
 					buffer.WriteString(child.GetHash())
 				}
 			}
 		}
 	}

 	return fmt.Sprintf("%x", md5.Sum(buffer.Bytes()))[:12]
 }

 // Get will retrieve the data for the current revision
 func (npr *NonPersistedRevision) Get(depth int) interface{} {
 	// 1. Clone the data to avoid any concurrent access issues
 	// 2. The current rev might still be pointing to an old config
 	//    thus, force the revision to get its latest value
 	latestRev := npr.GetBranch().GetLatest()
 	originalData := proto.Clone(latestRev.GetData().(proto.Message))
 	data := originalData

 	if depth != 0 {
 		// FIXME: Traversing the struct through reflection sometimes corrupts the data.
 		// Unlike the original python implementation, golang structs are not lazy loaded.
 		// Keeping this non-critical logic for now, but Get operations should be forced to
 		// depth=0 to avoid going through the following loop.
 		for fieldName, field := range ChildrenFields(latestRev.GetData()) {
 			childDataName, childDataHolder := GetAttributeValue(data, fieldName, 0)
 			if field.IsContainer {
 				for _, rev := range latestRev.GetChildren(fieldName) {
 					childData := rev.Get(depth - 1)
 					foundEntry := false
 					for i := 0; i < childDataHolder.Len(); i++ {
 						cdh_if := childDataHolder.Index(i).Interface()
 						if cdh_if.(proto.Message).String() == childData.(proto.Message).String() {
 							foundEntry = true
 							break
 						}
 					}
 					if !foundEntry {
 						// avoid duplicates by adding it only if the child was not found in the holder
 						childDataHolder = reflect.Append(childDataHolder, reflect.ValueOf(childData))
 					}
 				}
 			} else {
 				if revs := npr.GetBranch().GetLatest().GetChildren(fieldName); revs != nil && len(revs) > 0 {
 					rev := revs[0]
 					if rev != nil {
 						childData := rev.Get(depth - 1)
 						if reflect.TypeOf(childData) == reflect.TypeOf(childDataHolder.Interface()) {
 							childDataHolder = reflect.ValueOf(childData)
 						}
 					}
 				}
 			}
 			// Merge child data with cloned object
 			reflect.ValueOf(data).Elem().FieldByName(childDataName).Set(childDataHolder)
 		}
 	}

 	result := data

 	if result != nil {
 		// We need to send back a copy of the retrieved object
 		result = proto.Clone(data.(proto.Message))
 	}

 	return result
 }

 // UpdateData will refresh the data content of the revision
 func (npr *NonPersistedRevision) UpdateData(ctx context.Context, data interface{}, branch *Branch) Revision {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()

 	log.Debugw("update-data", log.Fields{"hash": npr.GetHash(), "current": npr.Config.Data, "provided": data})

 	// Do not update the revision if data is the same
 	if npr.Config.Data != nil && npr.Config.hashData(npr.Root, data) == npr.Config.Hash {
 		log.Debugw("stored-data-matches-latest", log.Fields{"stored": npr.Config.Data, "provided": data})
 		return npr
 	}

 	// Construct a new revision based on the current one
 	newRev := NonPersistedRevision{}
 	newRev.Config = NewDataRevision(npr.Root, data)
 	newRev.Hash = npr.Hash
 	newRev.Root = npr.Root
 	newRev.Name = npr.Name
 	newRev.Branch = branch
 	newRev.lastUpdate = npr.lastUpdate

 	newRev.Children = make(map[string][]Revision)
 	for entryName, childrenEntry := range branch.GetLatest().GetAllChildren() {
 		newRev.Children[entryName] = append(newRev.Children[entryName], childrenEntry...)
 	}

 	newRev.Finalize(false)

 	log.Debugw("update-data-complete", log.Fields{"updated": newRev.Config.Data, "provided": data})

 	return &newRev
 }

 // UpdateChildren will refresh the list of children with the provided ones
 // It will carefully go through the list and ensure that no child is lost
 func (npr *NonPersistedRevision) UpdateChildren(ctx context.Context, name string, children []Revision, branch *Branch) Revision {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()

 	// Construct a new revision based on the current one
 	updatedRev := &NonPersistedRevision{}
 	updatedRev.Config = NewDataRevision(npr.Root, npr.Config.Data)
 	updatedRev.Hash = npr.Hash
 	updatedRev.Branch = branch
 	updatedRev.Name = npr.Name
 	updatedRev.lastUpdate = npr.lastUpdate

 	updatedRev.Children = make(map[string][]Revision)
 	for entryName, childrenEntry := range branch.GetLatest().GetAllChildren() {
 		updatedRev.Children[entryName] = append(updatedRev.Children[entryName], childrenEntry...)
 	}

 	var updatedChildren []Revision

 	// Verify if the map contains already contains an entry matching the name value
 	// If so, we need to retain the contents of that entry and merge them with the provided children revision list
 	if existingChildren := branch.GetLatest().GetChildren(name); existingChildren != nil {
 		// Construct a map of unique child names with the respective index value
 		// for the children in the existing revision as well as the new ones
 		existingNames := make(map[string]int)
 		newNames := make(map[string]int)

 		for i, newChild := range children {
 			newNames[newChild.GetName()] = i
 		}

 		for i, existingChild := range existingChildren {
 			existingNames[existingChild.GetName()] = i

 			// If an existing entry is not in the new list, add it to the updated list, so it is not forgotten
 			if _, exists := newNames[existingChild.GetName()]; !exists {
 				updatedChildren = append(updatedChildren, existingChild)
 			}
 		}

 		log.Debugw("existing-children-names", log.Fields{"hash": npr.GetHash(), "names": existingNames})

 		// Merge existing and new children
 		for _, newChild := range children {
 			nameIndex, nameExists := existingNames[newChild.GetName()]

 			// Does the existing list contain a child with that name?
 			if nameExists {
 				// Check if the data has changed or not
 				if existingChildren[nameIndex].GetData().(proto.Message).String() != newChild.GetData().(proto.Message).String() {
 					log.Debugw("replacing-existing-child", log.Fields{
 						"old-hash": existingChildren[nameIndex].GetHash(),
 						"old-data": existingChildren[nameIndex].GetData(),
 						"new-hash": newChild.GetHash(),
 						"new-data": newChild.GetData(),
 					})

 					// replace entry
 					newChild.GetNode().SetRoot(existingChildren[nameIndex].GetNode().GetRoot())
 					updatedChildren = append(updatedChildren, newChild)
 				} else {
 					log.Debugw("keeping-existing-child", log.Fields{
 						"old-hash": existingChildren[nameIndex].GetHash(),
 						"old-data": existingChildren[nameIndex].GetData(),
 						"new-hash": newChild.GetHash(),
 						"new-data": newChild.GetData(),
 					})

 					// keep existing entry
 					updatedChildren = append(updatedChildren, existingChildren[nameIndex])
 				}
 			} else {
 				log.Debugw("adding-unknown-child", log.Fields{
 					"hash": newChild.GetHash(),
 					"data": newChild.GetData(),
 				})

 				// new entry ... just add it
 				updatedChildren = append(updatedChildren, newChild)
 			}
 		}

 		// Save children in new revision
 		updatedRev.SetChildren(name, updatedChildren)

 		updatedNames := make(map[string]int)
 		for i, updatedChild := range updatedChildren {
 			updatedNames[updatedChild.GetName()] = i
 		}

 		log.Debugw("updated-children-names", log.Fields{"hash": npr.GetHash(), "names": updatedNames})

 	} else {
 		// There are no children available, just save the provided ones
 		updatedRev.SetChildren(name, children)
 	}

 	updatedRev.Finalize(false)

 	return updatedRev
 }

 // UpdateAllChildren will replace the current list of children with the provided ones
 func (npr *NonPersistedRevision) UpdateAllChildren(children map[string][]Revision, branch *Branch) Revision {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()

 	newRev := npr
 	newRev.Config = npr.Config
 	newRev.Hash = npr.Hash
 	newRev.Branch = branch
 	newRev.Name = npr.Name
 	newRev.lastUpdate = npr.lastUpdate

 	newRev.Children = make(map[string][]Revision)
 	for entryName, childrenEntry := range children {
 		newRev.Children[entryName] = append(newRev.Children[entryName], childrenEntry...)
 	}
 	newRev.Finalize(false)

 	return newRev
 }

 // Drop is used to indicate when a revision is no longer required
 func (npr *NonPersistedRevision) Drop(txid string, includeConfig bool) {
 	log.Debugw("dropping-revision", log.Fields{"hash": npr.GetHash(), "name": npr.GetName()})
 }

 // ChildDrop will remove a child entry matching the provided parameters from the current revision
 func (npr *NonPersistedRevision) ChildDrop(childType string, childHash string) {
 	if childType != "" {
 		children := make([]Revision, len(npr.GetChildren(childType)))
 		copy(children, npr.GetChildren(childType))
 		for i, child := range children {
 			if child.GetHash() == childHash {
 				children = append(children[:i], children[i+1:]...)
 				npr.SetChildren(childType, children)
 				break
 			}
 		}
 	}
 }

 /// ChildDropByName will remove a child entry matching the type and name
 func (npr *NonPersistedRevision) ChildDropByName(childName string) {
 	// Extract device type
 	parts := strings.SplitN(childName, "/", 2)
 	childType := parts[0]

 	if childType != "" {
 		children := make([]Revision, len(npr.GetChildren(childType)))
 		copy(children, npr.GetChildren(childType))
 		for i, child := range children {
 			if child.GetName() == childName {
 				children = append(children[:i], children[i+1:]...)
 				npr.SetChildren(childType, children)
 				break
 			}
 		}
 	}
 }

 func (npr *NonPersistedRevision) SetLastUpdate(ts ...time.Time) {
 	npr.mutex.Lock()
 	defer npr.mutex.Unlock()

 	if ts != nil && len(ts) > 0 {
 		npr.lastUpdate = ts[0]
 	} else {
 		npr.lastUpdate = time.Now()
 	}
 }

 func (npr *NonPersistedRevision) GetLastUpdate() time.Time {
 	npr.mutex.RLock()
 	defer npr.mutex.RUnlock()

 	return npr.lastUpdate
 }

 func (npr *NonPersistedRevision) LoadFromPersistence(ctx context.Context, path string, txid string, blobs map[string]*kvstore.KVPair) []Revision {
 	// stub... required by interface
 	return nil
 }

 func (npr *NonPersistedRevision) SetupWatch(key string) {
 	// stub ... required by interface
 }

 func (npr *NonPersistedRevision) StorageDrop(txid string, includeConfig bool) {
 	// stub ... required by interface
 }

 func (npr *NonPersistedRevision) getVersion() int64 {
 	return -1
 }
	/*
	* Copyright 2018-present Open Networking Foundation

	* 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 model

	import (
	"bytes"
	"context"
	"crypto/md5"
	"fmt"
	"github.com/golang/protobuf/proto"
	"github.com/opencord/voltha-lib-go/pkg/db/kvstore"
	"github.com/opencord/voltha-lib-go/pkg/log"
	"reflect"
	"sort"
	"strings"
	"sync"
	"time"
	)

	// TODO: Cache logic will have to be revisited to cleanup unused entries in memory (disabled for now)
	//
	type revCacheSingleton struct {
	sync.RWMutex
	Cache sync.Map
	}

	func (s *revCacheSingleton) Get(path string) (interface{}, bool) {
	return s.Cache.Load(path)
	}
	func (s *revCacheSingleton) Set(path string, value interface{}) {
	s.Cache.Store(path, value)
	}
	func (s *revCacheSingleton) Delete(path string) {
	s.Cache.Delete(path)
	}

	var revCacheInstance *revCacheSingleton
	var revCacheOnce sync.Once

	func GetRevCache() *revCacheSingleton {
	revCacheOnce.Do(func() {
	revCacheInstance = &revCacheSingleton{Cache: sync.Map{}}
	})
	return revCacheInstance
	}

	type NonPersistedRevision struct {
	mutex sync.RWMutex
	Root *root
	Config *DataRevision
	childrenLock sync.RWMutex
	Children map[string][]Revision
	Hash string
	Branch *Branch
	WeakRef string
	Name string
	lastUpdate time.Time
	}

	func NewNonPersistedRevision(root root, branch Branch, data interface{}, children map[string][]Revision) Revision {
	r := &NonPersistedRevision{}
	r.Root = root
	r.Branch = branch
	r.Config = NewDataRevision(root, data)
	r.Children = children
	r.Hash = r.hashContent()
	return r
	}

	func (npr NonPersistedRevision) SetConfig(config DataRevision) {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()
	npr.Config = config
	}

	func (npr NonPersistedRevision) GetConfig() DataRevision {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()
	return npr.Config
	}

	func (npr *NonPersistedRevision) SetAllChildren(children map[string][]Revision) {
	npr.childrenLock.Lock()
	defer npr.childrenLock.Unlock()
	npr.Children = make(map[string][]Revision)

	for key, value := range children {
	npr.Children[key] = make([]Revision, len(value))
	copy(npr.Children[key], value)
	}
	}

	func (npr *NonPersistedRevision) SetChildren(name string, children []Revision) {
	npr.childrenLock.Lock()
	defer npr.childrenLock.Unlock()

	npr.Children[name] = make([]Revision, len(children))
	copy(npr.Children[name], children)
	}

	func (npr *NonPersistedRevision) GetAllChildren() map[string][]Revision {
	npr.childrenLock.Lock()
	defer npr.childrenLock.Unlock()

	return npr.Children
	}

	func (npr *NonPersistedRevision) GetChildren(name string) []Revision {
	npr.childrenLock.Lock()
	defer npr.childrenLock.Unlock()

	if _, exists := npr.Children[name]; exists {
	return npr.Children[name]
	}
	return nil
	}

	func (npr *NonPersistedRevision) SetHash(hash string) {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()
	npr.Hash = hash
	}

	func (npr *NonPersistedRevision) GetHash() string {
	//npr.mutex.Lock()
	//defer npr.mutex.Unlock()
	return npr.Hash
	}

	func (npr *NonPersistedRevision) ClearHash() {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()
	npr.Hash = ""
	}

	func (npr *NonPersistedRevision) GetName() string {
	//npr.mutex.Lock()
	//defer npr.mutex.Unlock()
	return npr.Name
	}

	func (npr *NonPersistedRevision) SetName(name string) {
	//npr.mutex.Lock()
	//defer npr.mutex.Unlock()
	npr.Name = name
	}
	func (npr NonPersistedRevision) SetBranch(branch Branch) {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()
	npr.Branch = branch
	}

	func (npr NonPersistedRevision) GetBranch() Branch {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()
	return npr.Branch
	}

	func (npr *NonPersistedRevision) GetData() interface{} {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()
	if npr.Config == nil {
	return nil
	}
	return npr.Config.Data
	}

	func (npr NonPersistedRevision) GetNode() node {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()
	return npr.Branch.Node
	}

	func (npr *NonPersistedRevision) Finalize(skipOnExist bool) {
	npr.Hash = npr.hashContent()
	}

	// hashContent generates a hash string based on the contents of the revision.
	// The string should be unique to avoid conflicts with other revisions
	func (npr *NonPersistedRevision) hashContent() string {
	var buffer bytes.Buffer
	var childrenKeys []string

	if npr.Config != nil {
	buffer.WriteString(npr.Config.Hash)
	}

	if npr.Name != "" {
	buffer.WriteString(npr.Name)
	}

	for key := range npr.Children {
	childrenKeys = append(childrenKeys, key)
	}

	sort.Strings(childrenKeys)

	if len(npr.Children) > 0 {
	// Loop through sorted Children keys
	for _, key := range childrenKeys {
	for _, child := range npr.Children[key] {
	if child != nil && child.GetHash() != "" {
	buffer.WriteString(child.GetHash())
	}
	}
	}
	}

	return fmt.Sprintf("%x", md5.Sum(buffer.Bytes()))[:12]
	}

	// Get will retrieve the data for the current revision
	func (npr *NonPersistedRevision) Get(depth int) interface{} {
	// 1. Clone the data to avoid any concurrent access issues
	// 2. The current rev might still be pointing to an old config
	// thus, force the revision to get its latest value
	latestRev := npr.GetBranch().GetLatest()
	originalData := proto.Clone(latestRev.GetData().(proto.Message))
	data := originalData

	if depth != 0 {
	// FIXME: Traversing the struct through reflection sometimes corrupts the data.
	// Unlike the original python implementation, golang structs are not lazy loaded.
	// Keeping this non-critical logic for now, but Get operations should be forced to
	// depth=0 to avoid going through the following loop.
	for fieldName, field := range ChildrenFields(latestRev.GetData()) {
	childDataName, childDataHolder := GetAttributeValue(data, fieldName, 0)
	if field.IsContainer {
	for _, rev := range latestRev.GetChildren(fieldName) {
	childData := rev.Get(depth - 1)
	foundEntry := false
	for i := 0; i < childDataHolder.Len(); i++ {
	cdh_if := childDataHolder.Index(i).Interface()
	if cdh_if.(proto.Message).String() == childData.(proto.Message).String() {
	foundEntry = true
	break
	}
	}
	if !foundEntry {
	// avoid duplicates by adding it only if the child was not found in the holder
	childDataHolder = reflect.Append(childDataHolder, reflect.ValueOf(childData))
	}
	}
	} else {
	if revs := npr.GetBranch().GetLatest().GetChildren(fieldName); revs != nil && len(revs) > 0 {
	rev := revs[0]
	if rev != nil {
	childData := rev.Get(depth - 1)
	if reflect.TypeOf(childData) == reflect.TypeOf(childDataHolder.Interface()) {
	childDataHolder = reflect.ValueOf(childData)
	}
	}
	}
	}
	// Merge child data with cloned object
	reflect.ValueOf(data).Elem().FieldByName(childDataName).Set(childDataHolder)
	}
	}

	result := data

	if result != nil {
	// We need to send back a copy of the retrieved object
	result = proto.Clone(data.(proto.Message))
	}

	return result
	}

	// UpdateData will refresh the data content of the revision
	func (npr NonPersistedRevision) UpdateData(ctx context.Context, data interface{}, branch Branch) Revision {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()

	log.Debugw("update-data", log.Fields{"hash": npr.GetHash(), "current": npr.Config.Data, "provided": data})

	// Do not update the revision if data is the same
	if npr.Config.Data != nil && npr.Config.hashData(npr.Root, data) == npr.Config.Hash {
	log.Debugw("stored-data-matches-latest", log.Fields{"stored": npr.Config.Data, "provided": data})
	return npr
	}

	// Construct a new revision based on the current one
	newRev := NonPersistedRevision{}
	newRev.Config = NewDataRevision(npr.Root, data)
	newRev.Hash = npr.Hash
	newRev.Root = npr.Root
	newRev.Name = npr.Name
	newRev.Branch = branch
	newRev.lastUpdate = npr.lastUpdate

	newRev.Children = make(map[string][]Revision)
	for entryName, childrenEntry := range branch.GetLatest().GetAllChildren() {
	newRev.Children[entryName] = append(newRev.Children[entryName], childrenEntry...)
	}

	newRev.Finalize(false)

	log.Debugw("update-data-complete", log.Fields{"updated": newRev.Config.Data, "provided": data})

	return &newRev
	}

	// UpdateChildren will refresh the list of children with the provided ones
	// It will carefully go through the list and ensure that no child is lost
	func (npr NonPersistedRevision) UpdateChildren(ctx context.Context, name string, children []Revision, branch Branch) Revision {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()

	// Construct a new revision based on the current one
	updatedRev := &NonPersistedRevision{}
	updatedRev.Config = NewDataRevision(npr.Root, npr.Config.Data)
	updatedRev.Hash = npr.Hash
	updatedRev.Branch = branch
	updatedRev.Name = npr.Name
	updatedRev.lastUpdate = npr.lastUpdate

	updatedRev.Children = make(map[string][]Revision)
	for entryName, childrenEntry := range branch.GetLatest().GetAllChildren() {
	updatedRev.Children[entryName] = append(updatedRev.Children[entryName], childrenEntry...)
	}

	var updatedChildren []Revision

	// Verify if the map contains already contains an entry matching the name value
	// If so, we need to retain the contents of that entry and merge them with the provided children revision list
	if existingChildren := branch.GetLatest().GetChildren(name); existingChildren != nil {
	// Construct a map of unique child names with the respective index value
	// for the children in the existing revision as well as the new ones
	existingNames := make(map[string]int)
	newNames := make(map[string]int)

	for i, newChild := range children {
	newNames[newChild.GetName()] = i
	}

	for i, existingChild := range existingChildren {
	existingNames[existingChild.GetName()] = i

	// If an existing entry is not in the new list, add it to the updated list, so it is not forgotten
	if _, exists := newNames[existingChild.GetName()]; !exists {
	updatedChildren = append(updatedChildren, existingChild)
	}
	}

	log.Debugw("existing-children-names", log.Fields{"hash": npr.GetHash(), "names": existingNames})

	// Merge existing and new children
	for _, newChild := range children {
	nameIndex, nameExists := existingNames[newChild.GetName()]

	// Does the existing list contain a child with that name?
	if nameExists {
	// Check if the data has changed or not
	if existingChildren[nameIndex].GetData().(proto.Message).String() != newChild.GetData().(proto.Message).String() {
	log.Debugw("replacing-existing-child", log.Fields{
	"old-hash": existingChildren[nameIndex].GetHash(),
	"old-data": existingChildren[nameIndex].GetData(),
	"new-hash": newChild.GetHash(),
	"new-data": newChild.GetData(),
	})

	// replace entry
	newChild.GetNode().SetRoot(existingChildren[nameIndex].GetNode().GetRoot())
	updatedChildren = append(updatedChildren, newChild)
	} else {
	log.Debugw("keeping-existing-child", log.Fields{
	"old-hash": existingChildren[nameIndex].GetHash(),
	"old-data": existingChildren[nameIndex].GetData(),
	"new-hash": newChild.GetHash(),
	"new-data": newChild.GetData(),
	})

	// keep existing entry
	updatedChildren = append(updatedChildren, existingChildren[nameIndex])
	}
	} else {
	log.Debugw("adding-unknown-child", log.Fields{
	"hash": newChild.GetHash(),
	"data": newChild.GetData(),
	})

	// new entry ... just add it
	updatedChildren = append(updatedChildren, newChild)
	}
	}

	// Save children in new revision
	updatedRev.SetChildren(name, updatedChildren)

	updatedNames := make(map[string]int)
	for i, updatedChild := range updatedChildren {
	updatedNames[updatedChild.GetName()] = i
	}

	log.Debugw("updated-children-names", log.Fields{"hash": npr.GetHash(), "names": updatedNames})

	} else {
	// There are no children available, just save the provided ones
	updatedRev.SetChildren(name, children)
	}

	updatedRev.Finalize(false)

	return updatedRev
	}

	// UpdateAllChildren will replace the current list of children with the provided ones
	func (npr NonPersistedRevision) UpdateAllChildren(children map[string][]Revision, branch Branch) Revision {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()

	newRev := npr
	newRev.Config = npr.Config
	newRev.Hash = npr.Hash
	newRev.Branch = branch
	newRev.Name = npr.Name
	newRev.lastUpdate = npr.lastUpdate

	newRev.Children = make(map[string][]Revision)
	for entryName, childrenEntry := range children {
	newRev.Children[entryName] = append(newRev.Children[entryName], childrenEntry...)
	}
	newRev.Finalize(false)

	return newRev
	}

	// Drop is used to indicate when a revision is no longer required
	func (npr *NonPersistedRevision) Drop(txid string, includeConfig bool) {
	log.Debugw("dropping-revision", log.Fields{"hash": npr.GetHash(), "name": npr.GetName()})
	}

	// ChildDrop will remove a child entry matching the provided parameters from the current revision
	func (npr *NonPersistedRevision) ChildDrop(childType string, childHash string) {
	if childType != "" {
	children := make([]Revision, len(npr.GetChildren(childType)))
	copy(children, npr.GetChildren(childType))
	for i, child := range children {
	if child.GetHash() == childHash {
	children = append(children[:i], children[i+1:]...)
	npr.SetChildren(childType, children)
	break
	}
	}
	}
	}

	/// ChildDropByName will remove a child entry matching the type and name
	func (npr *NonPersistedRevision) ChildDropByName(childName string) {
	// Extract device type
	parts := strings.SplitN(childName, "/", 2)
	childType := parts[0]

	if childType != "" {
	children := make([]Revision, len(npr.GetChildren(childType)))
	copy(children, npr.GetChildren(childType))
	for i, child := range children {
	if child.GetName() == childName {
	children = append(children[:i], children[i+1:]...)
	npr.SetChildren(childType, children)
	break
	}
	}
	}
	}

	func (npr *NonPersistedRevision) SetLastUpdate(ts ...time.Time) {
	npr.mutex.Lock()
	defer npr.mutex.Unlock()

	if ts != nil && len(ts) > 0 {
	npr.lastUpdate = ts[0]
	} else {
	npr.lastUpdate = time.Now()
	}
	}

	func (npr *NonPersistedRevision) GetLastUpdate() time.Time {
	npr.mutex.RLock()
	defer npr.mutex.RUnlock()

	return npr.lastUpdate
	}

	func (npr NonPersistedRevision) LoadFromPersistence(ctx context.Context, path string, txid string, blobs map[string]kvstore.KVPair) []Revision {
	// stub... required by interface
	return nil
	}

	func (npr *NonPersistedRevision) SetupWatch(key string) {
	// stub ... required by interface
	}

	func (npr *NonPersistedRevision) StorageDrop(txid string, includeConfig bool) {
	// stub ... required by interface
	}

	func (npr *NonPersistedRevision) getVersion() int64 {
	return -1
	}