add: db.load and save

interfaces/14-io-reader/_database_save.go

@@ -0,0 +1,133 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"reflect"
+)
+
+type database struct {
+	list  *list
+	types map[string]item // the registry of the types
+}
+
+// load the list by decoding the data from a json file.
+func (db *database) load(path string) error { // #v1
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(data, db)
+}
+
+// save the list by encoding the data to a json file.
+func (db *database) save(path string) error { // #v1
+	out, err := json.MarshalIndent(db, "", "\t")
+	if err != nil {
+		return err
+	}
+	return ioutil.WriteFile(path, out, 0644)
+}
+
+// #v2
+// func (db *database) load(r io.Reader) error {
+//  data, err := ioutil.ReadAll(r)
+// 	if err != nil {
+// 		return err
+// 	}
+// 	return json.Unmarshal(data, db)
+// }
+
+// #v3
+// TODO: use decoder
+
+// #v2
+// func (db *database) save(w io.Writer) error {
+// 	data, err := json.MarshalIndent(db, "", "\t")
+// 	if err != nil {
+// 		return err
+// 	}
+
+// 	_, err = io.Copy(w, bytes.NewReader(data))
+// 	return err
+// }
+
+// #v3
+// TODO: use encoder
+
+func (db *database) MarshalJSON() ([]byte, error) {
+	type encodable struct {
+		Type string
+		Item item
+	}
+
+	var e []encodable
+
+	for _, it := range *db.list {
+		// TypeOf -> finds the dynamic type of "it"
+		// Elem   -> returns the element type of the pointer
+		// Name   -> returns the type name as string
+		t := reflect.TypeOf(it).Elem().Name()
+		e = append(e, encodable{t, it})
+	}
+
+	return json.Marshal(e)
+}
+
+func (db *database) UnmarshalJSON(data []byte) error {
+	var decodables []struct {
+		Type string
+		Item json.RawMessage
+	}
+
+	if err := json.Unmarshal(data, &decodables); err != nil {
+		return err
+	}
+
+	for _, d := range decodables {
+		it, err := db.newItem(d.Item, d.Type)
+		if err != nil {
+			return err
+		}
+
+		*db.list = append(*db.list, it)
+	}
+
+	return nil
+}
+
+func (db *database) newItem(data []byte, typ string) (item, error) {
+	it, ok := db.types[typ]
+	if !ok {
+		return nil, fmt.Errorf("newItem: type (%q) does not exist", typ)
+	}
+
+	// get the dynamic type inside "it" like *book, *game, etc..
+	t := reflect.TypeOf(it)
+
+	// get the pointer type's element type like book, game, etc...
+	e := t.Elem()
+
+	// create a new pointer value of the type like new(book), new(game), etc...
+	v := reflect.New(e)
+
+	// get the interface value and cast it to the item type
+	it = v.Interface().(item)
+
+	return it, json.Unmarshal(data, &it)
+}
+
+func (db *database) register(typ string, it item) {
+	if db.types == nil {
+		db.types = make(map[string]item)
+	}
+	db.types[typ] = it
+}

interfaces/14-io-reader/_main_save.go

@@ -0,0 +1,40 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	var store list
+
+	db := database{list: &store}
+
+	// db.register("book", new(book))
+	// db.register("book", new(book))
+	// db.register("game", new(game))
+	// db.register("puzzle", new(puzzle))
+	// db.register("toy", new(toy))
+
+	// db.load("database.json")
+
+	store = list{
+		&book{product{"moby dick", 10}, toTimestamp(118281600)},
+		&book{product{"odyssey", 15}, toTimestamp("733622400")},
+		&book{product{"hobbit", 25}, unknown},
+		&puzzle{product{"rubik's cube", 5}},
+		&game{product{"minecraft", 20}},
+		&game{product{"tetris", 5}},
+		&toy{product{"yoda", 150}},
+	}
+
+	db.save("database.json")
+
+	fmt.Print(store)
+}

interfaces/14-io-reader/database.go

@@ -10,6 +10,7 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"io/ioutil"
 	"reflect"
 )
 
@@ -18,14 +19,14 @@ type database struct {
 	types map[string]item // the registry of the types
 }
 
-// #v1
-// func (db *database) load(path string) error {
-// 	data, err := ioutil.ReadFile(path)
-// 	if err != nil {
-// 		return err
-// 	}
-// 	return json.Unmarshal(data, db)
-// }
+// load the list by decoding the data from a json file.
+func (db *database) load(path string) error { // #v1
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(data, db)
+}
 
 // #v2
 // func (db *database) load(r io.Reader) error {
@@ -39,28 +40,6 @@ type database struct {
 // #v3
 // TODO: use decoder
 
-// #v1
-// func (db *database) save(path string) error {
-// 	data, err := json.MarshalIndent(db, "", "\t")
-// 	if err != nil {
-// 		return err
-// 	}
-// 	return ioutil.WriteFile(path, data, 0644)
-// }
-
-// #v2
-// func (db *database) save(w io.Writer) error {
-// 	data, err := json.MarshalIndent(db, "", "\t")
-// 	if err != nil {
-// 		return err
-// 	}
-//
-//  return io.Copy(w, bytes.NewReader(data))
-// }
-
-// #v3
-// TODO: use encoder
-
 func (db *database) MarshalJSON() ([]byte, error) {
 	type encodable struct {
 		Type string

interfaces/14-io-reader/database.json

@@ -51,4 +51,4 @@
 			"Price": 150
 		}
 	}
-]
+]

interfaces/14-io-reader/main.go

@@ -8,18 +8,10 @@
 package main
 
 import (
-	"encoding/json"
 	"fmt"
-	"io/ioutil"
-	"log"
 )
 
 func main() {
-	data, err := ioutil.ReadFile("database.json")
-	if err != nil {
-		log.Fatalln(err)
-	}
-
 	var store list
 
 	db := database{list: &store}
@@ -29,9 +21,7 @@ func main() {
 	db.register("puzzle", new(puzzle))
 	db.register("toy", new(toy))
 
-	if err := json.Unmarshal(data, &db); err != nil {
-		log.Fatalln(err)
-	}
+	db.load("database.json")
 
 	fmt.Print(store)