Make db name-literal agnostic

Move the persistence characteristic of the store into the graph registry
and provide an API hook to get that information.

Add error return for init on a non-persistent store.

Updates #35.

cayley.go

@@ -134,6 +134,6 @@ func main() {
 		flag.Usage()
 	}
 	if err != nil {
-		glog.Fatalln(err)
+		glog.Errorln(err)
 	}
 }

db/init.go

@@ -15,11 +15,20 @@
 package db
 
 import (
+	"errors"
+	"fmt"
+
 	"github.com/google/cayley/config"
 	"github.com/google/cayley/graph"
 )
 
+var ErrNotPersistent = errors.New("database type is not persistent")
+
 func Init(cfg *config.Config, triplePath string) error {
+	if !graph.IsPersistent(cfg.DatabaseType) {
+		return fmt.Errorf("ignoring unproductive database initialization request: %v", ErrNotPersistent)
+	}
+
 	err := graph.InitTripleStore(cfg.DatabaseType, cfg.DatabasePath, cfg.DatabaseOptions)
 	if err != nil {
 		return err

db/open.go

@@ -28,8 +28,7 @@ func Open(cfg *config.Config) (graph.TripleStore, error) {
 		return nil, err
 	}
 
-	// Memstore is not persistent, so it MUST be loaded.
-	if cfg.DatabaseType == "memstore" {
+	if !graph.IsPersistent(cfg.DatabaseType) {
 		err = Load(ts, cfg, cfg.DatabasePath)
 		if err != nil {
 			return nil, err

graph/leveldb/triplestore.go

@@ -34,7 +34,7 @@ import (
 )
 
 func init() {
-	graph.RegisterTripleStore("leveldb", newTripleStore, createNewLevelDB)
+	graph.RegisterTripleStore("leveldb", true, newTripleStore, createNewLevelDB)
 }
 
 const (

graph/memstore/triplestore.go

@@ -26,7 +26,7 @@ import (
 )
 
 func init() {
-	graph.RegisterTripleStore("memstore", func(string, graph.Options) (graph.TripleStore, error) {
+	graph.RegisterTripleStore("memstore", false, func(string, graph.Options) (graph.TripleStore, error) {
 		return newTripleStore(), nil
 	}, nil)
 }

graph/mongo/triplestore.go

@@ -30,7 +30,7 @@ import (
 )
 
 func init() {
-	graph.RegisterTripleStore("mongo", newTripleStore, createNewMongoGraph)
+	graph.RegisterTripleStore("mongo", true, newTripleStore, createNewMongoGraph)
 }
 
 // Guarantee we satisfy graph.Bulkloader.

graph/triplestore.go

@@ -136,38 +136,45 @@ type BulkLoader interface {
 type NewStoreFunc func(string, Options) (TripleStore, error)
 type InitStoreFunc func(string, Options) error
 
-var storeRegistry = make(map[string]NewStoreFunc)
-var storeInitRegistry = make(map[string]InitStoreFunc)
+type register struct {
+	newFunc      NewStoreFunc
+	initFunc     InitStoreFunc
+	isPersistent bool
+}
 
-func RegisterTripleStore(name string, newFunc NewStoreFunc, initFunc InitStoreFunc) {
+var storeRegistry = make(map[string]register)
+
+func RegisterTripleStore(name string, persists bool, newFunc NewStoreFunc, initFunc InitStoreFunc) {
 	if _, found := storeRegistry[name]; found {
 		panic("already registered TripleStore " + name)
 	}
-	storeRegistry[name] = newFunc
-	if initFunc != nil {
-		storeInitRegistry[name] = initFunc
+	storeRegistry[name] = register{
+		newFunc:      newFunc,
+		initFunc:     initFunc,
+		isPersistent: persists,
 	}
 }
 
 func NewTripleStore(name, dbpath string, opts Options) (TripleStore, error) {
-	newFunc, hasNew := storeRegistry[name]
-	if !hasNew {
+	r, registered := storeRegistry[name]
+	if !registered {
 		return nil, errors.New("triplestore: name '" + name + "' is not registered")
 	}
-	return newFunc(dbpath, opts)
+	return r.newFunc(dbpath, opts)
 }
 
 func InitTripleStore(name, dbpath string, opts Options) error {
-	initFunc, hasInit := storeInitRegistry[name]
-	if hasInit {
-		return initFunc(dbpath, opts)
-	}
-	if _, isRegistered := storeRegistry[name]; isRegistered {
-		return nil
+	r, registered := storeRegistry[name]
+	if registered {
+		return r.initFunc(dbpath, opts)
 	}
 	return errors.New("triplestore: name '" + name + "' is not registered")
 }
 
+func IsPersistent(name string) bool {
+	return storeRegistry[name].isPersistent
+}
+
 func TripleStores() []string {
 	t := make([]string, 0, len(storeRegistry))
 	for n := range storeRegistry {