A set of extentsion methods to get field names of indexes

LuceneIndexerExtensions.cs

using System.Collections.Generic;
using System.Linq;
using Examine.LuceneEngine.Providers;
using Lucene.Net.Index;
using Examine;

namespace UmbracoExamineApi
{
    public static class LuceneIndexerExtensions
    {
        /// <summary>
        /// Shortcut for getting field names of an index
        /// </summary>
        /// <param name="indexer"></param>
        /// <returns></returns>
        public static IEnumerable<string> GetFieldNames(this LuceneIndexer indexer) =>
            indexer.GetIndexWriter().GetReader().GetFieldNames(IndexReader.FieldOption.ALL);

        /// <summary>
        /// Shortcut for getting field names of an index by name
        /// </summary>
        /// <param name="indexerName"></param>
        /// <returns></returns>
        public static IEnumerable<string> GetFieldNames(this string indexerName) =>
            ((LuceneIndexer)ExamineManager.Instance.IndexProviderCollection[indexerName]).GetFieldNames();

        /// <summary>
        /// Shortcut for getting field names of multiple indexes
        /// </summary>
        /// <param name="indexers"></param>
        /// <returns></returns>
        public static IEnumerable<string> GetFieldNames(this IEnumerable<LuceneIndexer> indexers)
        {
            var names = new List<string>();
            foreach (var indexer in indexers)
                names.AddRange(indexer.GetFieldNames());
            return names.Distinct();
        }

        /// <summary>
        /// Shortcut for getting field names of multiple indexes by names
        /// </summary>
        /// <param name="indexerNames"></param>
        /// <returns></returns>
        public static IEnumerable<string> GetFieldNames(this IEnumerable<string> indexerNames)
        {
            var indexers = new List<LuceneIndexer>();
            foreach (var indexerName in indexerNames)
                indexers.Add((LuceneIndexer)ExamineManager.Instance.IndexProviderCollection[indexerName]);
            return indexers.GetFieldNames();
        }

    }

}