# XML Format

> Working with XML data in Orbital

Source: https://orbitalhq.com/docs/data-formats/xml

To declare that a type should be read/written as Xml, add the `com.orbitalhq.formats.Xml` annotation to a model:

```taxi
import com.orbitalhq.formats.Xml

@Xml
model Person {
  firstName : FirstName inherits String
}
```

## Declaring Attributes
By default, scalar items within a model are expected to be an Xml Element.

To declare something should be read / written as an attribute, use the `@lang.taxi.xml.XmlAttribute` annotation.

For example:

```taxi
  import com.orbitalhq.formats.Xml
> import lang.taxi.xml.XmlAttribute
  
  @Xml
  model Actor inherits Person {
>     @XmlAttribute
      id : ActorId 
      
      fullName : FullName
  }
```

Would read/write the following xml: 

```xml
<?xml version='1.0' encoding='UTF-8'?>
<Actor id="3">
    <fullName>Jimmy Smith</fullName>
</Actor>
```

## Collections
Collections are indicated by a repeating group with the attribute name.

For example:

```taxi
  @Xml
  model Movie {
>   actors : Actor[]
  }
```

would expect a repeated `actors` element:

```xml
<?xml version='1.0' encoding='UTF-8'?>
<Movie>
    <actors id="1">
        <firstName>Mel</firstName>
        <lastName>Gibson</lastName>
    </actors>
    <actors id="2">
        <firstName>Jack</firstName>
        <lastName>Spratt</lastName>
    </actors>
</Movie>
```

## Expressions
Expressions can be decalred on a model.

### Serializing
Expression values are written out as normal elements

### Deserializing
If an element or attribute is present for the field where the expression is declared,
the expression is ignored, and the value from the source is taken.

If there's no value present, then the expression is evaluated.

```taxi
import com.orbitalhq.formats.Xml
import lang.taxi.xml.XmlAttribute

@Xml
model Actor {
    firstName : FirstName inherits String
    lastName : LastName inherits String
    fullName : FullName inherits String = FirstName + ' ' + LastName
}
```

Given the following XML:

```xml
<?xml version='1.0' encoding='UTF-8'?>
<Actor id="3">
    <firstName>Jimmy</firstName>
    <lastName>Smith</lastName>
</Actor>
```

Then the value is read as: 

```json
{
  "firstName" : "Jimmy",
  "lastName" : "Smith",
  "fullName" : "Jimmy Smith"
}
```

## Using xpath() references

**Warning: Deprecated**
Using the `by xpath` tag is deprecated.

  Field names in the model are now used to match elements and attributes
 

It's possible (but discouraged) to use `by xpath("")` references to declare a column:

```taxi
model Person {
  firstName : FirstName by xpath("//fName")
}
```