WiX XmlConfig: Purpose for nesting XmlConfig in XmlConfig

wix, wix-extension, wix3.6, xml

Solution

The short answer: the only purpose of the option to have nested `<util:XmlConfig>` elements is to be able to add/remove attributes to/from the newly created elements in a more readable way. So, this is basically what you assumed.

Consider the following initial XML file:

<?xml version="1.0" encoding="utf-8"?>
<cars>
  <car name="ford" type="minivan"/>
  <car name="toyota" type="sedan"/>
  <motos>
    <moto name="honda" model="shadow" type="cruiser" />
  </motos>
</cars>

In order to add another `<moto>` to it, the following WiX snippet can be used:

<util:XmlConfig Id="elem1" Action="create" ElementPath="cars/motos" File="$(var.XmlFilePath)" Node="element" On="install" Name="moto">
  <util:XmlConfig Id="elem11" ElementId="elem1" Name="name" Value="yamaha" File="$(var.XmlFilePath)" />
  <util:XmlConfig Id="elem12" ElementId="elem1" Name="type" Value="chopper" File="$(var.XmlFilePath)" />
</util:XmlConfig>

As a result, the XML file ends up as follows:

<?xml version="1.0" encoding="utf-8"?>
<cars>
  <car name="ford" type="minivan"/>
  <car name="toyota" type="sedan"/>
  <motos>
    <moto name="honda" model="shadow" type="cruiser" />
    <moto name="yamaha" type="chopper" />
  </motos>
</cars>

Couple of things to note here:

- the `Action` attribute can't be defined in inner `XmlConfig` elements, and that's logical - it is the same as the one of the parent element

- the `Node` attribute can't be defined as well, because only attributes are allowed

- the weird thing is that you have to specify `File` attribute each time - seems to be a design issue here

- the `ElementId` attribute should point to the parent element you are adding the attributes to, and that's also strange as it could also be "guessed" from the nested code

Anyway, if you do want to create an XML subtree structure, the elements which end up as nested elements in resulting XML are made by `XmlConfig` elements placed on a same level. So, the following snippet:

<util:XmlConfig Id="elem1" Action="create" ElementPath="cars/motos" File="$(var.XmlFilePath)" Node="element" On="install" Name="moto" Sequence="1">
  <util:XmlConfig Id="elem11" ElementId="elem1" Name="name" Value="yamaha" File="$(var.XmlFilePath)" />
  <util:XmlConfig Id="elem12" ElementId="elem1" Name="type" Value="chopper" File="$(var.XmlFilePath)" />
</util:XmlConfig>
<util:XmlConfig Id="elem2" Action="create" ElementPath="cars/motos/moto[\[]@name='yamaha'[\]]" File="$(var.XmlFilePath)" Node="element" On="install" Name="extra" Sequence="2">
  <util:XmlConfig Id="elem21" ElementId="elem2" File="$(var.XmlFilePath)" Name="bags" Value="leather" />
</util:XmlConfig>

will transform the XML as follows:

<?xml version="1.0" encoding="utf-8"?>
<cars>
  <car name="ford" type="minivan"/>
  <car name="toyota" type="sedan"/>
  <motos>
    <moto name="honda" model="shadow" type="cruiser"/>
    <moto name="yamaha" type="chopper">
      <extra bags="leather"/>
    </moto>
  </motos>
</cars>

Pay attention to the following:

- the `XmlConfig` elements are placed on the same level, although they result in a nested elements in the resulting XML

- the `Sequence` attribute is important, in case you add an attribute or a child to the element, which is also being created

Hope this makes more sense now. Sorry for the wrong answer given initially.

Problem

What is the purpose and/or gain (other than increased readability for creating/deleting attributes) to nesting an `XmlConfig` element in another `XmlConfig` element? Example of what I'm referring to (I'm using WiX 3.6): ``` <util:XmlConfig ...> <util:XmlConfig ... /> </util:XmlConfig> ```

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