private Map<String, FieldMapping> getFieldMappings(final ElasticIndexDoc elasticIndex) {
        Map<String, FieldMapping> result = new TreeMap<>();

        if (elasticIndex.getClusterRef() != null) {
            try {
                final ElasticClusterDoc elasticCluster = elasticClusterStore.readDocument(elasticIndex.getClusterRef());
                result = elasticClientCache.contextResult(elasticCluster.getConnection(), elasticClient ->
                        getFlattenedFieldMappings(elasticIndex, elasticClient));
            } catch (final RuntimeException e) {
                LOGGER.error(e::getMessage, e);
            }
        }
        return result;
    }
Tests whether a field has the mapping property `index` set to `true`.
This determines whether it is searchable.
stroom-search/stroom-search-elastic/src/main/java/stroom/search/elastic/search/ElasticSearchProvider.java