use now creates a new book entry in the Dnote file.

cmd/new/new.go

@@ -1,9 +1,7 @@
 package new
 
 import (
-	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"time"
 
 	"github.com/dnote-io/cli/utils"
@@ -50,17 +48,7 @@ func writeNote(note utils.Note) error {
 		dnote[book] = []utils.Note{note}
 	}
 
-	d, err := json.MarshalIndent(dnote, "", "  ")
-	if err != nil {
-		return err
-	}
-
-	notePath, err := utils.GetDnotePath()
-	if err != nil {
-		return err
-	}
-
-	err = ioutil.WriteFile(notePath, d, 0644)
+	err := utils.WriteDnote(dnote)
 	if err != nil {
 		return err
 	}

main.go

@@ -75,6 +75,21 @@ func changeBook(bookName string) error {
 		return err
 	}
 
+	// Now add this book to the .dnote file, for issue #2
+	dnote, err := utils.GetDnote()
+	if err != nil {
+		return err
+	}
+
+	_, exists := dnote[bookName]
+	if exists == false {
+		dnote[bookName] = make([]utils.Note, 0)
+		err := utils.WriteDnote(dnote)
+		if err != nil {
+			return err
+		}
+	}
+
 	fmt.Printf("Now using %s\n", bookName)
 
 	return nil

utils/utils.go

@@ -12,6 +12,8 @@ import (
 	"strconv"
 	"time"
 
+	"github.com/dnote-io/cli/utils"
+
 	"gopkg.in/yaml.v2"
 )
 
@@ -167,6 +169,26 @@ func GetDnote() (Dnote, error) {
 	return ret, nil
 }
 
+// WriteDnote persists the state of Dnote into the dnote file
+func WriteDnote(dnote Dnote) error {
+	d, err := json.MarshalIndent(dnote, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	notePath, err := utils.GetDnotePath()
+	if err != nil {
+		return err
+	}
+
+	err = ioutil.WriteFile(notePath, d, 0644)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 // Deprecated. See upgrade/upgrade.go
 func GetNote() (YAMLDnote, error) {
 	ret := YAMLDnote{}