Golang : delete and modify XML file content

In our two previous tutorials on how to read XML file and how to create XML file, we have forgotten to show you how to modify and delete XML content :P

In this tutorial, we will use the standard library function to achieve the followings :

• Read an existing XML file(Employees.xml)

• Map the data to structs

• Add one new record

• Delete one record from the map

• Update the new record

• Save the date to a new XML file(LatestEmployees.xml)

Employees.xml

 <?xml version="1.0"?>
 <company>
 <staff>
 <id>101</id>
 <firstname>Derek</firstname>
 <lastname>Young</lastname>
 <username>derekyoung</username>
 </staff>
 <staff>
 <id>102</id>
 <firstname>John</firstname>
 <lastname>Smith</lastname>
 <username>johnsmith</username>
 </staff>

 </company>

This is the full source code :

modifyxml.go

 package main

  import (
 "fmt"
 "io/ioutil"
 "os"
 "encoding/xml"
 "io"
  )


  type Staff struct {
 XMLName xml.Name `xml:"staff"`
 ID int `xml:"id"`
 FirstName string `xml:"firstname"`
 LastName string `xml:"lastname"`
 UserName string `xml:"username"`
  }

  var staffmap map[string]Staff

  type Company struct {
 XMLName xml.Name `xml:"company"`
 Staffs []Staff `xml:"staff"`
  }

  func (s Staff) String() string {
 return fmt.Sprintf("\t ID : %d - FirstName : %s - LastName : %s - UserName : %s \n", s.ID,  s.FirstName , s.LastName, s.UserName)
  }

  func (s Staff) IDnum() int {
 return s.ID
  }

  func (s Staff) FName() string {
 return s.FirstName
  }

  func (s Staff) LName() string {
 return s.LastName
  }

  func (s Staff) UName() string {
 return s.UserName
  }


  func main() {
 xmlFile, err := os.Open("Employees.xml")
 if err != nil {
 fmt.Println("Error opening file:", err)
 return
 }
 defer xmlFile.Close()

 XMLdata, _ := ioutil.ReadAll(xmlFile)

 var c Company
 xml.Unmarshal(XMLdata, &c)


 // add one new record - we will modify this record in the map later
 c.Staffs = append(c.Staffs, Staff{ID: 103, FirstName: "Adam", LastName: "Ng", UserName: "huh?"})


 staffmap = make(map[string]Staff)

 // populate the map
 for _, staff := range c.Staffs {
 staffmap[staff.FName()] = Staff{ID : staff.IDnum(), FirstName : staff.FName(), LastName : staff.LName(), UserName : staff.UName()}
 }


 fmt.Println("Map BEFORE delete operation :")
 fmt.Println(staffmap)

 delete(staffmap,"Derek") // remove Derek from staffs

 fmt.Println("Map AFTER delete operation :")
 fmt.Println(staffmap)

 // modify staffmap["Adam"] - change ID to 108 and fix the huh? username
 staffmap["Adam"] = Staff{ID: 108, FirstName: "Adam", LastName: "Ng", UserName: "adamng"}


 fmt.Println("Map AFTER UPDATE operation :")
 fmt.Println(staffmap)

 // write to LatestEmployees.xml
 v := &Company{}

 for _, i := range staffmap {
 v.Staffs = append(v.Staffs, staffmap[i.FName()]) // remember we declared map[string]Staff above
 }

 filename := "LatestEmployees.xml"
 file, _ := os.Create(filename)

 xmlWriter := io.Writer(file)

 encoder := xml.NewEncoder(xmlWriter)
 encoder.Indent(" ", " ")
 if err := encoder.Encode(v); err != nil {
 fmt.Printf("error : %v\n", err)
 }
 encoder.Flush()
 fmt.Printf("Write operation to %s completed\n", filename)

 }

Executing modifyxml.go will produce the following output :

Map BEFORE delete operation :

map[Derek: ID : 101 - FirstName : Derek - LastName : Young - UserName : derekyoung

John: ID : 102 - FirstName : John - LastName : Smith - UserName : johnsmith

Adam: ID : 103 - FirstName : Adam - LastName : Ng - UserName : huh?

]

Map AFTER delete operation :

map[Adam: ID : 103 - FirstName : Adam - LastName : Ng - UserName : huh?

John: ID : 102 - FirstName : John - LastName : Smith - UserName : johnsmith

]

Map AFTER UPDATE operation :

map[John: ID : 102 - FirstName : John - LastName : Smith - UserName : johnsmith

Adam: ID : 108 - FirstName : Adam - LastName : Ng - UserName : adamng

]

Write operation to LatestEmployees.xml completed

and the content of LatestEmployees.xml :

  <company>
 <staff>
 <id>102</id>
 <firstname>John</firstname>
 <lastname>Smith</lastname>
 <username>johnsmith</username>
 </staff>
 <staff>
 <id>108</id>
 <firstname>Adam</firstname>
 <lastname>Ng</lastname>
 <username>adamng</username>
 </staff>
  </company>

Hope this tutorial will be helpful to those learning Go and XML.

Note :

There should be better 3rd party solution to handle XML file in Golang. This tutorial uses the standard library.