Having WiX upgrade a config file with missing items

Question

I am just starting to use WiX as my installation framework for my existing application. The application has an App.Config file that controls various customer-specific settings. The majority of these settings are modified in-house, and are not user-controllable.

An example of such a config file would be:

[...snip]
<applicationSettings>
    <setting name="DatabaseConnectionString" serializeAs="String">
        <value>Data Source=localhost;Initial Catalog=CustomersDatabase;Persist Security Info=True;Integrated Security=True</value>
    </setting>
</applicationSettings>
[snip...]

When a newer version of the application is delivered, it will have a stock configuation file, which includes any new app settings:

[...snip]
<applicationSettings>
    <setting name="DatabaseConnectionString" serializeAs="String">
        <value>Data Source=localhost;Initial Catalog=NonProductionDatabase;Persist Security Info=True;Integrated Security=True</value>
    </setting>
    <setting name="NewConfigItem" serializeAs="String">
        <value>ConfigDetails</value>
    </setting>
</applicationSettings>
[snip...]

I would like to setup my WiX installer to, during an upgrade, create a merged App.Config, such that the existing settings are untouched, but that new config items are inserted with their default values:

[...snip]
<applicationSettings>
    <setting name="DatabaseConnectionString" serializeAs="String">
        <value>Data Source=localhost;Initial Catalog=CustomersDatabase;Persist Security Info=True;Integrated Security=True</value>
    </setting>
    <setting name="NewConfigItem" serializeAs="String">
        <value>ConfigDetails</value>
    </setting>
</applicationSettings>
[snip...]

However, I do not want the installer to have to know beforehand what the configuration options are; I simply want it to scan the existing file, and add new options from the installer if any are found missing.

Is this possible?

Answer 1

Yes, you'll need to write a custom action to read the existing xml file. I would then recommend adding temporary records to the XmlConfig table as described in this question based on the read data.