gistfile1.cs

public static IDocumentResult<T> ExtractKeyAndInsert<T>(this IBucket bucket, string json, string fieldNameForId, out string id)
{
    var type = typeof (T);
    var document = type == typeof (object) ?
        GetDocumentForDynamic<T>(json, fieldNameForId, out id) :
        GetDocumentForPOCO<T>(type, json, fieldNameForId, out id);

    return bucket.Insert(document);
}

static IDocument<T> GetDocumentForDynamic<T>(string json, string fieldNameForId, out string id)
{
    var jObject = JsonConvert.DeserializeObject<JObject>(json);
    Document<T> document;

    JToken value = null;
    if (jObject.TryGetValue(fieldNameForId, out value))
    {
        jObject.Remove(fieldNameForId);
        document = new Document<T>
        {
            Id = id = value.ToString(),
            Content = JsonConvert.DeserializeObject<T>(jObject.ToString())
        };
    }
    else
    {
        throw new ArgumentException("Cannot find id field in json.", fieldNameForId);
    }
    return document;
}

private static IDocument<T> GetDocumentForPOCO<T>(Type type, string json, string fieldNameForId, out string id)
{
    var document = new Document<T>
    {
        Content = JsonConvert.DeserializeObject<T>(json)
    };

    var idProperty = type.GetProperty(fieldNameForId);
    if (idProperty == null)
    {
        throw new ArgumentException("Cannot find id field in json.", fieldNameForId);
    }
    id = idProperty.GetValue(document.Content).ToString();
    document.Id = id;
    return document;
}