TermsFacetFor<> - properties of objects in IEnumerables

TermsFacetExtensions.cs

public static class TermsFacetExtensions
{
    public static ITypeSearch<TSource> TermsFacetFor<TSource, TListItem>(this ITypeSearch<TSource> search, Expression<Func<TSource, IEnumerable<TListItem>>> fieldListSelector, Expression<Func<TListItem, object>> fieldListItemSelector)
    {
        fieldListSelector.ValidateNotNullArgument("fieldListSelector");
        fieldListItemSelector.ValidateNotNullArgument("fieldListItemSelector");

        var facetName = fieldListSelector.GetFieldPath() + "." + fieldListItemSelector.GetFieldPath();
        var fieldName = search.Client.Conventions.FieldNameConvention.GetFieldName(fieldListSelector) + "." + search.Client.Conventions.FieldNameConvention.GetFieldName(fieldListItemSelector);
        
        return new Search<TSource, IQuery>(search, context =>
        {
            var facetRequest = new TermsFacetRequest(facetName);
            facetRequest.Field = fieldName;
            context.RequestBody.Facets.Add(facetRequest);
        });
    }

    public static TermsFacet TermsFacetFor<TResult, TListItem>(this IHasFacetResults<TResult> facetsResultsContainer, Expression<Func<TResult, IEnumerable<TListItem>>> fieldListSelector, Expression<Func<TListItem, object>> fieldListItemSelector)
    {
        fieldListSelector.ValidateNotNullArgument("fieldListSelector");
        fieldListItemSelector.ValidateNotNullArgument("fieldListItemSelector");

        var facetName = fieldListSelector.GetFieldPath() + "." + fieldListItemSelector.GetFieldPath();

        var facet = facetsResultsContainer.Facets[facetName];
        if (facet.IsNull())
        {
            return null;
        }

        return facet as TermsFacet;
    }
}

TermsFacetForExample.cs

// Document
public class DocumentListObject
{
    public string Name { get; set; }
}

public class Document
{
    public Document()
    {
        DocumentListObjects = new List<DocumentListObject>();
    }

    public string Name { get; set; }

    public List<DocumentListObject> DocumentListObjects { get; set; }
}

// query
var result = client.Search<Document>()
                        .TermsFacetFor(x => x.DocumentListObjects, x => x.Name)
                        .GetResult();

var facet = result.TermsFacetFor(x => x.DocumentListObjects, x => x.Name);