CODEWITHSUNDEEP
go
Dac0d3r
Dac0d3r

Reputation: 1854

Error when trying to xml.Unmarshal to struct with field of type map[string]interface{}

The problem is that xml.Unmarshal of a struct with a field of type map[string]interface{} will fail with the error:

unknown type map[string]interface {}
{XMLName:{Space: Local:myStruct} Name:test Meta:map[]}

Since the Meta field of type map[string]interface{} is as far as I can define, what's inside has to be dynamically unmarshalled.

package main

import (
    "encoding/xml"
    "fmt"
)

func main() {
    var myStruct MyStruct

    // meta is as far as we know, inside meta, dynamic properties and nesting will happen
    s := `<myStruct>
        <name>test</name>
        <meta>
            <someProp>something</someProp>
            <someOtherDynamic>
                <name>test</name>
                <somethingElse>test2</somethingElse>
                <nested3>
                    <name>nested3</name>
                    <nested3elements>
                        <elem>ele1</elem>
                        <elem>ele2</elem>
                    </nested3elements>
                </nested3>
            </someOtherDynamic>
        </meta>
    </myStruct>`

    err := xml.Unmarshal([]byte(s), &myStruct)
    if err == nil {
        fmt.Printf("%+v\n", myStruct)
    } else {
        fmt.Println(err)
        fmt.Printf("%+v\n", myStruct)
    }
}

type MyStruct struct {
    XMLName xml.Name               `xml:"myStruct"`
    Name    string                 `xml:"name"`
    Meta    map[string]interface{} `xml:"meta,omitempty"`
}

I've made an example here: http://play.golang.org/p/lTDJzXXPwT

How can I achieve this?

My workaround "solution" so far:

http://play.golang.org/p/gQUlvkYl7k

Basically what happens is that:

  1. The Meta field got the xml annotations removed, thus being ignore from the xml.Unmashal
  2. New type, MapContainer, is created with a field: InnerXML []byte xml:",innerxml"
  3. MetaByte field of type MapContainer is added using the xml:"meta,omitempty" annotations

So in the first xml.Unmarshal we save a byte slice of the meta element's XML. Then in our custom xml unmarshal function we take that byteSlice and use the magic function NewMapXml from the mxj package, and set the Meta field of the struct to this newly created map.

This is possible thanks to the genius made this repo, https://github.com/clbanning/mxj , which can unmarshal from XML to maps.

Updated current best solution:

http://play.golang.org/p/_tw06klods

Thanks to Adam Vincze

Upvotes: 1

Views: 2690

Answers (1)

Adam Vincze
Adam Vincze

Reputation: 871

depending what you need to do with meta at the end you might want to take a look at this lib: https://github.com/clbanning/mxj

you could do it just a little nicer if you implement a custom UnmarshalXML function

func (m *MyStruct) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
    var v struct {
        XMLName xml.Name `xml:"myStruct"`
        Name    string   `xml:"name"`
        Meta    struct {
            Inner []byte `xml:",innerxml"`
        } `xml:"meta"`
    }


    err := d.DecodeElement(&v, &start)
    if err != nil {
        return err
    }

    m.Name = v.Name
    myMap := make(map[string]interface{})
    // ... do the mxj magic here ... -
    // fill myMap
    m.Meta = myMap


    return nil
}

type MyStruct struct {
    Name    string
    Meta    map[string]interface{}
}

`

that leaves your MyStruct nice and clean

Upvotes: 3

Related Questions