I would like to map empty value from tag to nill value in my object e.g. I have this xml

<Address>
   <city>city</city>
   <streetNumber></streetNumber>
</Address>

a my type is

type Address struct{
   city string `xml:"city"`
   streetNumber *int `xml:"streetNumber"`
}

and in this case streetNumber is 0 but when I delete tag streetNumber from xml value is nil Is it possible to map streetNumber tag to nil when it is empty?

CodePudding user response：

You may want to look at making streetNumber its own type with custom marshaling like what they're doing here with time format: https://www.programming-books.io/essential/go/custom-xml-marshaling-aa8105fe264b4b198647cbc718480ba1

I'd lean towards the int Valid bool combo but you could do an int pointer.

Edit: updated to include a potential implementation of marshal/unmarshal.

type Address struct {
    City         string       `xml:"city"`
    StreetNumber StreetNumber `xml:"streetNumber"`
}

type StreetNumber struct {
    Value int
    Valid bool
}

func (s StreetNumber) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
    // If the address is null/unset/invalid, we serialize an empty string as the value.
    v := ""
    if s.Valid {
        // The address has a value so we convert the integer to string.
        v = strconv.Itoa(s.Value)
    }

    // Encode the string `v` to the XML element.
    return e.EncodeElement(v, start)
}

func (s *StreetNumber) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
    // Assume the value is invalid so we can just shortcut out.
    s.Valid = false
    s.Value = 0;
    
    var v string
    if err := d.DecodeElement(&v, &start); err != nil {
        // Forward the error if it failed to decode the raw XML
        return err
    }

    if v == "" {
        // The value was empty, but this is just the 3rd null state, not an error.
        return nil
    }

    i, err := strconv.Atoi(v)
    if err != nil {
        // The element value was not an integer so this is an invalid state -- forward the error.
        return err
    }

    // The street number was a valid integer.
    s.Valid = true
    s.Value = i

    return nil
}