Add feature to bind a single element to an array on ConfigurationBinder. #57325
Description
Background and motivation
Currently with the JSON Configuration Provider you can do:
{
"tvshow": {
"metadata": [
{
"name": "PrisonBreak"
}
]
}
}and then bind to without any problem:
public class TvShow
{
public Metadata[] Metadata { get; set; }
}
public class Metadata
{
public string Name { get; set; }
}However if we want to bind to this from the xml configuration provider using:
<TvShow>
<Metadata>
<Name>Prison Break</Name>
</Metadata>
</TvShow>We don't have a way to know that TvShows can contain multiple Metadata elements and that is bound to an array, so we fail to bind when a single element is provided as the key doesn't contain any index in the target array as the binder expects when binding to an array, and we return a Metadata[] with a null object.
In order to fix this we would need to change the binder to account for a key without the index suffix when the child elements don't contain any index (a single element); but this would be breaking for other providers where this is not expected. Consider changing the original JSON so that tvshows is an object with a single metadata, this would bind even though json is not specifying an array:
{
"tvshow": {
"metadata": {
"name": "PrisonBreak"
}
}We want to introduce a new flag to enable this behavior.
API Proposal
namespace Microsoft.Extensions.Configuration
{
public class BinderOptions
{
public bool BindSingleElementsToArray { get; set; }
}
}API Usage
With the given xml example above.
var configuration = new ConfigurationBuilder().AddXmlFile("MyFile.xml").Build();
var tvShow = new tvShow();
configuration.Bind(tvShow, o => { o.BindSingleElementsToArray = true });Risks
This would be a breaking change and could impact perf a little bit but only if the flag is set to true.