c# - Bind netcore IConfigurationSection to a dynamic object

Question

In my appSettings.json, I have a configuration section that can contain anything as long as it's json valid. It is usally a set of key/value (string/string)

I would like to get it in my code and return it in a controller call.

I took a look at the source code (https://github.com/aspnet/Configuration/blob/6d9519622b5db2c5ac6bafa8bcdb25fe27914de3/src/Config.Binder/ConfigurationBinder.cs ) and it seems I am doomed with off-the-shelves solutions.

If I limit the use case to key value pairs, I can use the AsEnumerable() in the IConfigSection and that's fine. If I want to allow lists, then I may still be ok parsing the keys to look for :Number but does someone has a way to easily deserialize a random object ? Or even better get the configuration section as is without deserializing it.

For example

{
 "mySettings": 
 {
   "key1": "value1",
   "key2": "value2",
   "list": [ "item1", "item2", "item3" ],
   "complexObject": {
     "key": "value",
     "anything" :  [{"id": "3", "name": "John"}]
   }
 }
}

Answer 1

It's possible if you abuse .NET 4 dynamic objects. As you said, you can enumerate over all keys in the config, and they all follow the same pattern. With your example, all the keys of interest are:

mySettings null 
mySettings:list null 
mySettings:list:2 item3 
mySettings:list:1 item2 
mySettings:list:0 item1 
mySettings:key3 value3 
mySettings:key2 value2 
mySettings:key1 value1 
mySettings:complexObject null 
mySettings:complexObject:key value 
mySettings:complexObject:anything null 
mySettings:complexObject:anything:0 null 
mySettings:complexObject:anything:0:name John 
mySettings:complexObject:anything:0:id 3 

From this, we can build an ExpandoObject, like so:

[HttpGet]
public IActionResult Get([FromServices] IConfiguration config)
{
    var result = new ExpandoObject();

    // retrieve all keys from your settings
    var configs = config.AsEnumerable().Where(_ => _.Key.StartsWith("mySettings"));
    foreach(var kvp in configs) 
    {
        var parent = result as IDictionary<string, object>;
        var path = kvp.Key.Split(':');

        // create or retrieve the hierarchy (keep last path item for later)
        var i = 0;
        for (i = 0; i < path.Length - 1; i++)
        {
            if (!parent.ContainsKey(path[i]))
            {
                parent.Add(path[i], new ExpandoObject());
            }

            parent = parent[path[i]] as IDictionary<string, object>;
        }

        if (kvp.Value == null)
            continue;

        // add the value to the parent
        // note: in case of an array, key will be an integer and will be dealt with later
        var key = path[i];
        parent.Add(key, kvp.Value);
    }

    // at this stage, all arrays are seen as dictionaries with integer keys
    ReplaceWithArray(null, null, result);

    return Ok(result);
}

private void ReplaceWithArray(ExpandoObject parent, string key, ExpandoObject input) 
{
    if (input == null)
        return;

    var dict = input as IDictionary<string, object>;
    var keys = dict.Keys.ToArray();

    // it's an array if all keys are integers
    if (keys.All(k => int.TryParse(k, out var dummy))) {
        var array = new object[keys.Length];
        foreach(var kvp in dict) {
            array[int.Parse(kvp.Key)] = kvp.Value;
            // Edit: If structure is nested deeper we need this next line 
            ReplaceWithArray(input, kvp.Key, kvp.Value as ExpandoObject);
        }

        var parentDict = parent as IDictionary<string, object>;
        parentDict.Remove(key);
        parentDict.Add(key, array);
    }
    else
    {
        foreach (var childKey in dict.Keys.ToList())
        {
            ReplaceWithArray(input, childKey, dict[childKey] as ExpandoObject);
        }
    }
}

Note: since the colon : is used as separator, you can't have a key that contains a colon.

Finally, because you now have a dynamic object, you can directly get its properties:

dynamic asDym = result;
string name = asDym.mySettings.complexObject.anything[0].name;