NestedTermsFacetExtensions for EPiServer Find

gistfile1.cs

public static class NestedTermsFacetExtensions
{
    public static ITypeSearch<TSource> NestedTermsFacetFor<TSource, TEnumerable>(
        this ITypeSearch<TSource> search,
        Expression<Func<TSource, IEnumerable<TEnumerable>>> enumerableFieldSelector, Expression<Func<TEnumerable, string>> itemFieldSelector)
    {
        return search.AddNestedTermsFacetFor(enumerableFieldSelector, itemFieldSelector, null);
    }

    public static ITypeSearch<TSource> NestedTermsFacetFor<TSource, TEnumerable>(
        this ITypeSearch<TSource> search,
        Expression<Func<TSource, IEnumerable<TEnumerable>>> enumerableFieldSelector, Expression<Func<TEnumerable, string>> itemFieldSelector, Action<TermsFacetRequest> facetRequestAction)
    {
        return search.AddNestedTermsFacetFor(enumerableFieldSelector, itemFieldSelector, facetRequestAction);
    }

    public static ITypeSearch<TSource> AddNestedTermsFacetFor<TSource>(
        this ITypeSearch<TSource> search,
        Expression enumerableFieldSelector, Expression itemFieldSelector, Action<TermsFacetRequest> facetRequestAction)
    {
        enumerableFieldSelector.ValidateNotNullArgument("enumerableFieldSelector");
        itemFieldSelector.ValidateNotNullArgument("itemFieldSelector");

        var facetName = enumerableFieldSelector.GetFieldPath() + "." + itemFieldSelector.GetFieldPath();
        var fieldName = enumerableFieldSelector.GetFieldPath() + "." + search.Client.Conventions.FieldNameConvention.GetFieldName(itemFieldSelector);
        var action = facetRequestAction;
        return search.TermsFacetFor(facetName, x =>
        {
            x.Field = fieldName;
            if (action.IsNotNull())
            {
                action(x);
            }
        });
    }
}

public static class NestedTermsFacetResultExtraction
{
    private static TFacet GetFacetFor<TFacet>(IHasFacetResults facetsResultsContainer, string facetName)
        where TFacet : Facet
    {
        var facet = facetsResultsContainer.Facets[facetName];
        if (facet.IsNull())
        {
            return null;
        }

        return facet as TFacet;
    }

    public static TermsFacet NestedTermsFacetFor<TResult, TEnumerable>(
        this IHasFacetResults<TResult> facetsResultsContainer, Expression<Func<TResult, IEnumerable<TEnumerable>>> enumerableFieldSelector, Expression<Func<TEnumerable, string>> itemFieldSelector)
    {
        return GetFacetFor<TermsFacet>(facetsResultsContainer, enumerableFieldSelector.GetFieldPath() + "." + itemFieldSelector.GetFieldPath());
    }
}

gistfile2.cs

// Usage
// Given:

 public class BlogPost
{
  public int Id { get; set; }

  public string Title { get; set; }

  public string Content { get; set; }

  public IEnumerable<Author> Authors { get; set; }
  
  ...
}

public class Author : User, IHasTitle
{
  public string Name { get; set; }
  
  ...
}

// Request facet:

var searchResult = client.Search<BlogPost>().NestedTermsFacetFor(x => x.Authors, x => x.Name).GetResult();

// Get facet:

var termsFacet = searchResult.NestedTermsFacetFor(x => x.Authors(), x => x.Name);