需求和思路

在一般的小项目或者一个小软件,例如客户端之类的小程序中,可能会需要数据的持久化.但是使用一般的数据库(Mysql)之类的不合适.使用sqlite3这种嵌入式的是个较好的方法,但是Go语言中sqlite3的库是C语言的,Cgo不支持跨平台编译.正是由于这种需求,才想到使用json格式将数据直接保存在文件中.
具体的思路是怎么样呢"color: #ff0000">查询操作

这种操作的实现比较简单,直接将文件中的数据读取出来,使用json库反序列化就可以了. 代码如下 :

type Product struct {
  Name string `json:"name"`
  Num int  `json:"num"`
}

func findAll() {
  ps := make([]Product, 0)

  data, err := ioutil.ReadFile("./index.json")
  if err != nil {
    log.Fatal(err)
  }

  // 这里参数要指定为变量的地址
  err = json.Unmarshal(data, &ps)
  if err != nil {
    log.Fatal(err)
  }

  fmt.Println(ps)
}

添加操作

添加的实现实在查询的基础上的,我们需要先查询文件中的数据库,并转化为map格式,再将struct也转化为map格式(这里要使用反射),合并map,json序列化,最后保存在文件中.代码如下:

func create() {
  fields := make([]map[string]interface{}, 0)
  
  p1 := &Product{
    Name: "Blog",
    Num: 2,
  }
  
  _, _ = json.Marshal(p1)
  // 读取文件中的数据,保存为map格式
  data, _ := ioutil.ReadFile("./index.json")
  err := json.Unmarshal(data, &fields)
  if err != nil {
    log.Fatal(err)
  }
  
  // 使用反射将struct转化为map
  tp := reflect.TypeOf(p1).Elem()
  vp := reflect.ValueOf(p1).Elem()
  field := make(map[string]interface{}, 0)
  for i := 0; i < tp.NumField(); i++ {
    field1 := tp.Field(i)
    field2 := vp.Field(i)
    key := field1.Tag.Get("json")
    field[key] = field2.Interface()
  }
  // 合并map
  fields = append(fields, field)
  
  // 写入文件
  out, _ := json.Marshal(fields)
  _ = ioutil.WriteFile("./index.json", out, 0755)
}

条件查询

思路: 将struct转化为map,根据输入的条件查询.查询的结果转化为struct.代码如下:

func FindOne() {
  product := &Product{}

  p1 := &Product{
    Name: "John",
    Num: 23,
  }

  // 使用反射将struct转化为map
  tp := reflect.TypeOf(p1).Elem()
  vp := reflect.ValueOf(p1).Elem()
  field := make(map[string]interface{}, 0)
  for i := 0; i < tp.NumField(); i++ {
    field1 := tp.Field(i)
    field2 := vp.Field(i)
    key := field1.Tag.Get("json")
    switch field2.Kind() {
    case reflect.Int:
      field[key] = float64(field2.Interface().(int))
    case reflect.Int8:
      field[key] = float64(field2.Interface().(int8))
    case reflect.Int16:
      field[key] = float64(field2.Interface().(int16))
    case reflect.Int32:
      field[key] = float64(field2.Interface().(int32))
    case reflect.Int64:
      field[key] = float64(field2.Interface().(int64))
    case reflect.Uint:
      field[key] = float64(field2.Interface().(uint))
    case reflect.Uint8:
      field[key] = float64(field2.Interface().(uint8))
    case reflect.Uint16:
      field[key] = float64(field2.Interface().(uint16))
    case reflect.Uint32:
      field[key] = float64(field2.Interface().(uint32))
    case reflect.Uint64:
      field[key] = float64(field2.Interface().(uint64))
    case reflect.Float32:
      field[key] = float64(field2.Interface().(float32))
    case reflect.Float64:
      field[key] = field2.Interface()
    default:
      field[key] = field2.Interface()
    }
  }

  _, _ = json.Marshal(p1)
  // 读取文件中的数据,保存为map格式
  // 数据转化为map时,数值类型的统一变成float64
  data, _ := ioutil.ReadFile("./index.json")
  fields := make([]map[string]interface{}, 0)
  err := json.Unmarshal(data, &fields)
  if err != nil {
    log.Fatal(err)
  }

  // 查询的条件
  columns := []string{"name", "num"}
  length := len(columns)
  for _, item := range fields {
    for i := 0; i < length; i++ {
      // 这里的比较需要改进
      if item[columns[i]] != field[columns[i]] {
        break
      }
      if i == length-1 {
        field = item
        goto OVER
      }
    }
  }
OVER:
  fmt.Println(field)

  out, _ := json.Marshal(field)
  _ = json.Unmarshal(out, &product)

  fmt.Println(product)
}

修改操作

修改操作在查询操作的基础上实现, 修改操作需要有一个id值,能确定元素的唯一性.代码如下:

func Update() {
  p1 := &Product{
    Id:  "2bbec87025968879c3c9682abe3bf730",
    Name: "John_e",
    Num: 100,
  }

  // 使用反射将struct转化为map
  tp := reflect.TypeOf(p1).Elem()
  vp := reflect.ValueOf(p1).Elem()
  field := make(map[string]interface{}, 0)
  for i := 0; i < tp.NumField(); i++ {
    field1 := tp.Field(i)
    field2 := vp.Field(i)
    key := field1.Tag.Get("json")
    switch field2.Kind() {
    case reflect.Int:
      field[key] = float64(field2.Interface().(int))
    case reflect.Int8:
      field[key] = float64(field2.Interface().(int8))
    case reflect.Int16:
      field[key] = float64(field2.Interface().(int16))
    case reflect.Int32:
      field[key] = float64(field2.Interface().(int32))
    case reflect.Int64:
      field[key] = float64(field2.Interface().(int64))
    case reflect.Uint:
      field[key] = float64(field2.Interface().(uint))
    case reflect.Uint8:
      field[key] = float64(field2.Interface().(uint8))
    case reflect.Uint16:
      field[key] = float64(field2.Interface().(uint16))
    case reflect.Uint32:
      field[key] = float64(field2.Interface().(uint32))
    case reflect.Uint64:
      field[key] = float64(field2.Interface().(uint64))
    case reflect.Float32:
      field[key] = float64(field2.Interface().(float32))
    case reflect.Float64:
      field[key] = field2.Interface()
    default:
      field[key] = field2.Interface()
    }
  }

  _, _ = json.Marshal(p1)
  // 读取文件中的数据,保存为map格式
  // 数据转化为map时,数值类型的统一变成float64
  data, _ := ioutil.ReadFile("./index.json")
  fields := make([]map[string]interface{}, 0)
  err := json.Unmarshal(data, &fields)
  if err != nil {
    log.Fatal(err)
  }

  // 修改的条件
  columns := []string{"name", "num"}
  for _, v := range fields {
    if v["_id"] == field["_id"] {
      for _, col := range columns {
        v[col] = field[col]
      }
      field = v
    }
  }

  out, _ := json.MarshalIndent(fields, "", " ")
  _ = ioutil.WriteFile("./index.json", out, 0755)
}

删除操作

最后就是删除操作了,这个比较思路简单,输入唯一的id值,删除对应的字段,再保存到文件就可以了.代码如下:

func Delete() {
  p1 := &Product{
    Id:  "db43fa2d4f69cddce7494941cb36032b",
    Name: "John_e",
    Num: 100,
  }

  _, _ = json.Marshal(p1)
  // 读取文件中的数据,保存为map格式
  // 数据转化为map时,数值类型的统一变成float64
  data, _ := ioutil.ReadFile("./index.json")
  fields := make([]map[string]interface{}, 0)
  err := json.Unmarshal(data, &fields)
  if err != nil {
    log.Fatal(err)
  }

  length := len(fields)
  for index, field := range fields {
    if field["_id"] == p1.Id {
      if index == length - 1 {
        fields = fields[0:index]
      } else {
        fields = append(fields[0:index], fields[index+1:]...)
      }
    }
  }

  out, _ := json.MarshalIndent(fields, "", " ")
  _ = ioutil.WriteFile("./index.json", out, 0755)
}

完整版

最后在附上完整版代码:

package store

import (
  "bytes"
  "crypto/md5"
  "encoding/json"
  "errors"
  "fmt"
  "io/ioutil"
  "os"
  "path/filepath"
  "reflect"
  "strings"
  "time"
)

type Store struct {
  Dir string
}

func NewStore(dir string) (*Store, error) {

  // .开头的为相对路径,补全为全路径
  if strings.HasPrefix(dir, ".") {
    pwd, _ := os.Getwd()
    dir = filepath.Join(pwd, dir)
  }
  store := &Store{Dir: dir}

  st, err := os.Stat(dir)
  if err != nil {
    err = os.Mkdir(dir, 0755)
    if err != nil {
      return nil, err
    }
  } else if st != nil && !st.IsDir() {
    return nil, errors.New("file already exists")
  }

  return store, nil
}

// 创建与结构体对应的json文件
func (s *Store) Sync(values ...interface{}) error {
  for _, v := range values {
    tb := parseTn(v)
    if tb == "" {
      return errors.New("does not find store")
    }
    _path := filepath.Join(s.Dir, tb)
    _, err := os.Stat(_path)
    if err != nil {
      _ = ioutil.WriteFile(_path, []byte("[]"), 0755)
    }
  }
  return nil
}

// 删除所有
func (s *Store) Destroy() error {
  return os.RemoveAll(s.Dir)
}

func (s *Store) FindAll(v interface{}) error {

  _path, err := s.before(v)
  if err != nil {
    return err
  }

  out, err := s.readAll(_path)
  if err != nil {
    return err
  }
  err = json.Unmarshal(out, &v)
  return err
}

func (s *Store) FindOne(v interface{}, columns ...string) (interface{}, error) {

  _path, err := s.before(v)
  if err != nil {
    return nil, err
  }

  data, err := s.readAll(_path)
  if err != nil {
    return nil, err
  }

  fields := make([]map[string]interface{}, 0)
  err = json.Unmarshal(data, &fields)
  if err != nil {
    return nil, err
  }

  m := structToMap(v)
  length := len(columns)
  for _, item := range fields {
    for i := 0; i < length; i++ {
      // TODO 这里的比较需要改进
      if item[columns[i]] != m[columns[i]] {
        break
      }
      if i == length-1 {
        m = item
        goto OVER
      }
    }
  }
OVER:

  err = mapToStruct(m, &v)
  if err != nil {
    return nil, err
  }

  return v, nil
}

func (s *Store) Create(v interface{}) error {

  _path, err := s.before(v)
  if err != nil {
    return err
  }

  data, err := s.readAll(_path)
  if err != nil {
    return err
  }

  fields := make([]map[string]interface{}, 0)
  err = json.Unmarshal(data, &fields)
  if err != nil {
    return err
  }

  m := structToMap(v)
  m["_id"] = randId()

  fields = append(fields, m)

  err = s.writeAll(_path, fields)
  if err != nil {
    return err
  }

  err = mapToStruct(m, v)
  if err != nil {
    return err
  }

  return nil
}

func (s *Store) Update(v interface{}, columns ...string) error {

  _path, err := s.before(v)
  if err != nil {
    return err
  }

  data, err := s.readAll(_path)
  if err != nil {
    return err
  }

  fields := make([]map[string]interface{}, 0)
  err = json.Unmarshal(data, &fields)
  if err != nil {
    return err
  }

  m := structToMap(v)
  for _, v := range fields {
    if v["_id"] == m["_id"] {
      for _, col := range columns {
        v[col] = m[col]
      }
      m = v
    }
  }

  err = s.writeAll(_path, fields)
  if err != nil {
    return err
  }

  return nil
}

func (s *Store) Delete(v interface{}) error {

  _path, err := s.before(v)
  if err != nil {
    return err
  }

  data, err := s.readAll(_path)
  if err != nil {
    return err
  }

  fields := make([]map[string]interface{}, 0)
  err = json.Unmarshal(data, &fields)
  if err != nil {
    return err
  }

  m := structToMap(v)
  length := len(fields)
  for index, field := range fields {
    if field["_id"] == m["_id"] {
      if index == length-1 {
        fields = fields[0:index]
      } else {
        fields = append(fields[0:index], fields[index+1:]...)
      }
    }
  }

  err = s.writeAll(_path, fields)
  if err != nil {
    return err
  }

  return nil
}

func (s *Store) Clean(v interface{}) error {
  _path, err := s.before(v)
  if err != nil {
    return err
  }

  return os.Remove(_path)
}

func (s *Store) readAll(file string) ([]byte, error) {
  out, err := ioutil.ReadFile(file)
  if err != nil {
    return nil, err
  }
  return out, nil
}

func (s *Store) writeAll(file string, v interface{}) error {
  out, err := json.MarshalIndent(v, "", " ")
  if err != nil {
    return err
  }

  err = ioutil.WriteFile(file, out, 0755)
  if err != nil {
    return err
  }

  return nil
}

func (s *Store) before(v interface{}) (string, error) {
  tb := parseTn(v)
  if tb == "" {
    return "", errors.New("invalid table name")
  }

  _path := filepath.Join(s.Dir, tb)
  _, err := os.Stat(_path)
  if err != nil {
    return "", err
  }

  return _path, nil
}

func structToMap(v interface{}) map[string]interface{} {
  tp := reflect.TypeOf(v).Elem()
  vp := reflect.ValueOf(v).Elem()
  field := make(map[string]interface{}, 0)
  for i := 0; i < tp.NumField(); i++ {
    field1 := tp.Field(i)
    field2 := vp.Field(i)
    key := field1.Tag.Get("json")
    field[key] = field2.Interface()
    switch field2.Kind() {
    case reflect.Int:
      field[key] = float64(field2.Interface().(int))
    case reflect.Int8:
      field[key] = float64(field2.Interface().(int8))
    case reflect.Int16:
      field[key] = float64(field2.Interface().(int16))
    case reflect.Int32:
      field[key] = float64(field2.Interface().(int32))
    case reflect.Int64:
      field[key] = float64(field2.Interface().(int64))
    case reflect.Uint:
      field[key] = float64(field2.Interface().(uint))
    case reflect.Uint8:
      field[key] = float64(field2.Interface().(uint8))
    case reflect.Uint16:
      field[key] = float64(field2.Interface().(uint16))
    case reflect.Uint32:
      field[key] = float64(field2.Interface().(uint32))
    case reflect.Uint64:
      field[key] = float64(field2.Interface().(uint64))
    case reflect.Float32:
      field[key] = float64(field2.Interface().(float32))
    case reflect.Float64:
      field[key] = field2.Interface()
    default:
      field[key] = field2.Interface()
    }
  }

  return field
}

func mapToStruct(m map[string]interface{}, v interface{}) error {
  out, err := json.Marshal(m)
  if err != nil {
    return err
  }
  return json.Unmarshal(out, &v)
}

func toSnake(s string) string {
  out := bytes.Buffer{}

  bName := []byte(s)

  point := 0
  for index, b := range bName {
    // 非大写,不需要转化
    if b < 65 || b > 90 || index-point < 2 {
      out.WriteByte(b)
      continue
    }
    // 首字符大写,直接转化为小写
    if index == 0 {
      out.WriteByte(b + 32)
      point = index
    }
    // 连续三个大写,触发转化
    if index-point >= 2 {
      out.WriteByte(95)
      out.WriteByte(b + 32)
      point = index
    }
  }

  return out.String()
}

func parseTn(v interface{}) string {
  var name string

  tp := reflect.TypeOf(v).Elem()
  switch tp.Kind() {
  case reflect.Ptr:
    sp := strings.Split(tp.String(), ".")
    name = sp[len(sp)-1]
  case reflect.Slice:
    sp := strings.Split(tp.String(), ".")
    name = sp[len(sp)-1]
  case reflect.Struct:
    name = tp.Name()
  }
  name = toSnake(name)
  return name + ".json"
}

func randId() string {
  return fmt.Sprintf("%x", md5.Sum([]byte(time.Now().String())))
}
华山资源网 Design By www.eoogi.com
广告合作:本站广告合作请联系QQ:858582 申请时备注:广告合作(否则不回)
免责声明:本站资源来自互联网收集,仅供用于学习和交流,请遵循相关法律法规,本站一切资源不代表本站立场,如有侵权、后门、不妥请联系本站删除!
华山资源网 Design By www.eoogi.com