xml - Parse XML to struct containing slice

Question

Situation:

I have this XML structure:

<group id="26659127">
    <member ref="292403538"/>
    <member ref="298884289"/>
    <member ref="261728686"/>
    <info k="name" v="omega"/>
    <info k="rank" v="16"/>
</group>

I need to convert this XML into this struct:

{
    Id: "26659127",
    Members: ["26659127", "298884289", "261728686"],
    Info: [
        {
            Key: "name",
            Value: "omega"
        },
        {
            Key: "rank",
            Value: "16"
        }
    ]
}

Problem:

I created a struct for parsing XML already:

type Group struct {
    Id      string   `xml:"id,attr"`
    Members []string `xml:" "`
    Info    []Info   `xml:"info"`
}

type Info struct {
    Key     string   `xml:"k,attr"`
    Value   string   `xml:"v,attr"`
}

But, as you can see I haven't defined an expression for Members yet. Actually, I tried putting xml:"member,ref,attr" and xml:"member:ref,attr" in here, but it didn't work.

Question:

Is there a possibility to solve this issue? If yes, what expression I should use?

标签： xmlparsinggostructslice

Answer 1

Unfortunately there is no way to use the default XML unmarshaler to achieve your goal by using only struct field tags so you'll have to either:

1. Extract a struct type for the "Members" field which has a "ref" field (similar to the "Info" type).
2. Use a custom type for "Member" which is a string and implements xml.Unmarshaler by extracting the value of the "ref" attribute from the associated XML element.

Here is an example of how you can implement strategy #2 above (Go Playground):

type Group struct {
  Id      string      `xml:"id,attr"`
  Members []MemberRef `xml:"member"`
  Info    []Info      `xml:"info"`
}

type MemberRef string

func (m *MemberRef) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
  *m = MemberRef(start.Attr[0].Value) // Assume only the "ref" attribute exists.
  _, err := d.Token() // Consume and discard the synthetic xml.EndElement.
  return err
}

// ...
var group Group
err := xml.Unmarshal([]byte(xmlstr), &group)
if err != nil {
    panic(err)
}
fmt.Printf("%#v\n", group)
// main.Group{Id:"26659127", Members:[]main.MemberRef{"292403538", "298884289", "261728686"}, Info:...

Note that you can even marshal this struct directly into the example JSON format you listed:

bs, err := json.MarshalIndent(group, "", "  ")
if err != nil {
    panic(err)
}
fmt.Println(string(bs))
// {
//   "Id": "26659127",
//   "Members": [
//     "292403538",
//     "298884289",
//     "261728686"
//   ],
//   "Info": [
//     ...