Deserializing tag with attribute values into Map

[alex-semov]

Assume we have below xml structure:

<container>
  <attr>
    <name>Name</name>
    <desc>Description</desc>
  </attr>
</container>

when <attr> tag doesn't have attribute values, quick-xml parses successfully into Map (HashMap, MultiMap)
Container ( "attr" : { Name(Name), Desc(Description) } )

#[derive(Deserialize, PartialEq)]
pub enum AttrDefChoice {
    Name(String),
    Desc(String),
}

#[derive(Deserialize, PartialEq)]
pub enum ContainerDef {
    Container(MultiMap<String, AttrDefChoice>),
}

but when <attr> have name value I need some wrapper struct with rename = "$value". In that case it works only with attr: Vec<AttrDefChoice>.

<container>
  <attr name="AttrName">
    <name>Name</name>
    <desc>Description</desc>
  </attr>
</container>

...

#[derive(Deserialize, PartialEq)]
pub struct AttrDef {
    name: String,

    #[serde(rename = "$value")]
    attr: MultiMap<String, AttrDefChoice>,
}

invalid type: string "Name", expected internally tagged enum AttrDefChoice

Is there any way to achieve parsing of tags with values into Map?

[Mingun]

Generally, this is the same problem as #241 -- you have a struct with a field, that could get all internal markup of an XML node

<>
  <name>Name</name>
  <desc>Description</desc>
</>

Conceptually, there is no such a defined mapping from XML to Rust in quick-xml for that. You may think, that $value is supposed for that, and I agree with that, but $value semantic also is not defined precisily. To define such semantics, I opened #369.

It is certain that we require two kinds of $value:

• $value which should mean map any (unconsumed?) elements of the field, so that

  <>
  text
  </>

  <>
  <![CDATA[content]]>
  </>

  <>
    <tag attribute="value">content</tag>
    <tag2/>
  </>

  all mapped to a dedicated field
• #text which should mean to map only text/CDATA content and raise an error if markup is encountered.

The current $value does something middle of that two.

[snystrom]

I think I have a related issue, but want to confirm. Say I have the following structure:

<upper>
   <inner name = "a">1</inner>
   <inner name = "b">2</inner>
   <inner name = "c">3</inner>
</upper>

Ideally, I'd like to deserialize into the following:

{upper: {inner: {"a" : 1, "b" : 2, "c" : 3}}}

Do I have to write a custom deserializer impl for this?

[Mingun]

Yes, probably this is somehow related.

Your JSON example can be modelled by the following Rust code:

struct Upper {
  inner: Inner,
}
struct Inner {
  a: usize,
  b: usize,
  c: usize,
}

In XML this struct will be represented as

<any-tag>
  <inner a="1" b="2" c="3"/>
</any-tag>

or

<any-tag>
  <inner>
    <a>1</a>
    <b>1</b>
    <c>1</c>
  </inner>
</any-tag>

I think, that your original XML should be modelled as

struct Upper {
  inner: Vec<Inner>,
}
#[serde(tag = "name", content = "$value")]
enum Inner {
  a(usize),
  b(usize),
  c(usize),
}

(where $value matters, which I described above), but I have feeling that this not work currently (even if you ignore the consequences of the fact that due to serde-rs/serde#1183 it will not work with usize).

So if you want to get the Rust representation closer to your JSON representation, you in any case need the custom (de)serializer.