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graphdb.go
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graphdb.go
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package graphdb
import (
"database/sql"
"fmt"
"path"
"strings"
"sync"
)
const (
createEntityTable = `
CREATE TABLE IF NOT EXISTS entity (
id text NOT NULL PRIMARY KEY
);`
createEdgeTable = `
CREATE TABLE IF NOT EXISTS edge (
"entity_id" text NOT NULL,
"parent_id" text NULL,
"name" text NOT NULL,
CONSTRAINT "parent_fk" FOREIGN KEY ("parent_id") REFERENCES "entity" ("id"),
CONSTRAINT "entity_fk" FOREIGN KEY ("entity_id") REFERENCES "entity" ("id")
);
`
createEdgeIndices = `
CREATE UNIQUE INDEX IF NOT EXISTS "name_parent_ix" ON "edge" (parent_id, name);
`
)
// Entity with a unique id
type Entity struct {
id string
}
// An Edge connects two entities together
type Edge struct {
EntityID string
Name string
ParentID string
}
type Entities map[string]*Entity
type Edges []*Edge
type WalkFunc func(fullPath string, entity *Entity) error
// Graph database for storing entities and their relationships
type Database struct {
conn *sql.DB
mux sync.RWMutex
}
func IsNonUniqueNameError(err error) bool {
str := err.Error()
// sqlite 3.7.17-1ubuntu1 returns:
// Set failure: Abort due to constraint violation: columns parent_id, name are not unique
if strings.HasSuffix(str, "name are not unique") {
return true
}
// sqlite-3.8.3-1.fc20 returns:
// Set failure: Abort due to constraint violation: UNIQUE constraint failed: edge.parent_id, edge.name
if strings.Contains(str, "UNIQUE constraint failed") && strings.Contains(str, "edge.name") {
return true
}
// sqlite-3.6.20-1.el6 returns:
// Set failure: Abort due to constraint violation: constraint failed
if strings.HasSuffix(str, "constraint failed") {
return true
}
return false
}
// Create a new graph database initialized with a root entity
func NewDatabase(conn *sql.DB, init bool) (*Database, error) {
if conn == nil {
return nil, fmt.Errorf("Database connection cannot be nil")
}
db := &Database{conn: conn}
if init {
if _, err := conn.Exec(createEntityTable); err != nil {
return nil, err
}
if _, err := conn.Exec(createEdgeTable); err != nil {
return nil, err
}
if _, err := conn.Exec(createEdgeIndices); err != nil {
return nil, err
}
rollback := func() {
conn.Exec("ROLLBACK")
}
// Create root entities
if _, err := conn.Exec("BEGIN"); err != nil {
return nil, err
}
if _, err := conn.Exec("INSERT INTO entity (id) VALUES (?);", "0"); err != nil {
rollback()
return nil, err
}
if _, err := conn.Exec("INSERT INTO edge (entity_id, name) VALUES(?,?);", "0", "/"); err != nil {
rollback()
return nil, err
}
if _, err := conn.Exec("COMMIT"); err != nil {
return nil, err
}
}
return db, nil
}
// Close the underlying connection to the database
func (db *Database) Close() error {
return db.conn.Close()
}
// Set the entity id for a given path
func (db *Database) Set(fullPath, id string) (*Entity, error) {
db.mux.Lock()
defer db.mux.Unlock()
rollback := func() {
db.conn.Exec("ROLLBACK")
}
if _, err := db.conn.Exec("BEGIN EXCLUSIVE"); err != nil {
return nil, err
}
var entityId string
if err := db.conn.QueryRow("SELECT id FROM entity WHERE id = ?;", id).Scan(&entityId); err != nil {
if err == sql.ErrNoRows {
if _, err := db.conn.Exec("INSERT INTO entity (id) VALUES(?);", id); err != nil {
rollback()
return nil, err
}
} else {
rollback()
return nil, err
}
}
e := &Entity{id}
parentPath, name := splitPath(fullPath)
if err := db.setEdge(parentPath, name, e); err != nil {
rollback()
return nil, err
}
if _, err := db.conn.Exec("COMMIT"); err != nil {
return nil, err
}
return e, nil
}
// Return true if a name already exists in the database
func (db *Database) Exists(name string) bool {
db.mux.RLock()
defer db.mux.RUnlock()
e, err := db.get(name)
if err != nil {
return false
}
return e != nil
}
func (db *Database) setEdge(parentPath, name string, e *Entity) error {
parent, err := db.get(parentPath)
if err != nil {
return err
}
if parent.id == e.id {
return fmt.Errorf("Cannot set self as child")
}
if _, err := db.conn.Exec("INSERT INTO edge (parent_id, name, entity_id) VALUES (?,?,?);", parent.id, name, e.id); err != nil {
return err
}
return nil
}
// Return the root "/" entity for the database
func (db *Database) RootEntity() *Entity {
return &Entity{
id: "0",
}
}
// Return the entity for a given path
func (db *Database) Get(name string) *Entity {
db.mux.RLock()
defer db.mux.RUnlock()
e, err := db.get(name)
if err != nil {
return nil
}
return e
}
func (db *Database) get(name string) (*Entity, error) {
e := db.RootEntity()
// We always know the root name so return it if
// it is requested
if name == "/" {
return e, nil
}
parts := split(name)
for i := 1; i < len(parts); i++ {
p := parts[i]
if p == "" {
continue
}
next := db.child(e, p)
if next == nil {
return nil, fmt.Errorf("Cannot find child for %s", name)
}
e = next
}
return e, nil
}
// List all entities by from the name
// The key will be the full path of the entity
func (db *Database) List(name string, depth int) Entities {
db.mux.RLock()
defer db.mux.RUnlock()
out := Entities{}
e, err := db.get(name)
if err != nil {
return out
}
children, err := db.children(e, name, depth, nil)
if err != nil {
return out
}
for _, c := range children {
out[c.FullPath] = c.Entity
}
return out
}
// Walk through the child graph of an entity, calling walkFunc for each child entity.
// It is safe for walkFunc to call graph functions.
func (db *Database) Walk(name string, walkFunc WalkFunc, depth int) error {
children, err := db.Children(name, depth)
if err != nil {
return err
}
// Note: the database lock must not be held while calling walkFunc
for _, c := range children {
if err := walkFunc(c.FullPath, c.Entity); err != nil {
return err
}
}
return nil
}
// Return the children of the specified entity
func (db *Database) Children(name string, depth int) ([]WalkMeta, error) {
db.mux.RLock()
defer db.mux.RUnlock()
e, err := db.get(name)
if err != nil {
return nil, err
}
return db.children(e, name, depth, nil)
}
// Return the refrence count for a specified id
func (db *Database) Refs(id string) int {
db.mux.RLock()
defer db.mux.RUnlock()
var count int
if err := db.conn.QueryRow("SELECT COUNT(*) FROM edge WHERE entity_id = ?;", id).Scan(&count); err != nil {
return 0
}
return count
}
// Return all the id's path references
func (db *Database) RefPaths(id string) Edges {
db.mux.RLock()
defer db.mux.RUnlock()
refs := Edges{}
rows, err := db.conn.Query("SELECT name, parent_id FROM edge WHERE entity_id = ?;", id)
if err != nil {
return refs
}
defer rows.Close()
for rows.Next() {
var name string
var parentId string
if err := rows.Scan(&name, &parentId); err != nil {
return refs
}
refs = append(refs, &Edge{
EntityID: id,
Name: name,
ParentID: parentId,
})
}
return refs
}
// Delete the reference to an entity at a given path
func (db *Database) Delete(name string) error {
db.mux.Lock()
defer db.mux.Unlock()
if name == "/" {
return fmt.Errorf("Cannot delete root entity")
}
parentPath, n := splitPath(name)
parent, err := db.get(parentPath)
if err != nil {
return err
}
if _, err := db.conn.Exec("DELETE FROM edge WHERE parent_id = ? AND name = ?;", parent.id, n); err != nil {
return err
}
return nil
}
// Remove the entity with the specified id
// Walk the graph to make sure all references to the entity
// are removed and return the number of references removed
func (db *Database) Purge(id string) (int, error) {
db.mux.Lock()
defer db.mux.Unlock()
rollback := func() {
db.conn.Exec("ROLLBACK")
}
if _, err := db.conn.Exec("BEGIN"); err != nil {
return -1, err
}
// Delete all edges
rows, err := db.conn.Exec("DELETE FROM edge WHERE entity_id = ?;", id)
if err != nil {
rollback()
return -1, err
}
changes, err := rows.RowsAffected()
if err != nil {
return -1, err
}
// Delete entity
if _, err := db.conn.Exec("DELETE FROM entity where id = ?;", id); err != nil {
rollback()
return -1, err
}
if _, err := db.conn.Exec("COMMIT"); err != nil {
return -1, err
}
return int(changes), nil
}
// Rename an edge for a given path
func (db *Database) Rename(currentName, newName string) error {
db.mux.Lock()
defer db.mux.Unlock()
parentPath, name := splitPath(currentName)
newParentPath, newEdgeName := splitPath(newName)
if parentPath != newParentPath {
return fmt.Errorf("Cannot rename when root paths do not match %s != %s", parentPath, newParentPath)
}
parent, err := db.get(parentPath)
if err != nil {
return err
}
rows, err := db.conn.Exec("UPDATE edge SET name = ? WHERE parent_id = ? AND name = ?;", newEdgeName, parent.id, name)
if err != nil {
return err
}
i, err := rows.RowsAffected()
if err != nil {
return err
}
if i == 0 {
return fmt.Errorf("Cannot locate edge for %s %s", parent.id, name)
}
return nil
}
type WalkMeta struct {
Parent *Entity
Entity *Entity
FullPath string
Edge *Edge
}
func (db *Database) children(e *Entity, name string, depth int, entities []WalkMeta) ([]WalkMeta, error) {
if e == nil {
return entities, nil
}
rows, err := db.conn.Query("SELECT entity_id, name FROM edge where parent_id = ?;", e.id)
if err != nil {
return nil, err
}
defer rows.Close()
for rows.Next() {
var entityId, entityName string
if err := rows.Scan(&entityId, &entityName); err != nil {
return nil, err
}
child := &Entity{entityId}
edge := &Edge{
ParentID: e.id,
Name: entityName,
EntityID: child.id,
}
meta := WalkMeta{
Parent: e,
Entity: child,
FullPath: path.Join(name, edge.Name),
Edge: edge,
}
entities = append(entities, meta)
if depth != 0 {
nDepth := depth
if depth != -1 {
nDepth -= 1
}
entities, err = db.children(child, meta.FullPath, nDepth, entities)
if err != nil {
return nil, err
}
}
}
return entities, nil
}
// Return the entity based on the parent path and name
func (db *Database) child(parent *Entity, name string) *Entity {
var id string
if err := db.conn.QueryRow("SELECT entity_id FROM edge WHERE parent_id = ? AND name = ?;", parent.id, name).Scan(&id); err != nil {
return nil
}
return &Entity{id}
}
// Return the id used to reference this entity
func (e *Entity) ID() string {
return e.id
}
// Return the paths sorted by depth
func (e Entities) Paths() []string {
out := make([]string, len(e))
var i int
for k := range e {
out[i] = k
i++
}
sortByDepth(out)
return out
}