How to combine query_string and terms query about elasticsearch-net HOT 5 CLOSED

public class SearchQueryDescriptor
{
  public string Query { get; set; }
  public string Sort { get; set; }
  //selected facets
  public Dictionary<string, List<string>> Facets { get; set; }
  public int Page { get; set; }
  public bool UseFacetting { get; set; }

  //some global boolean filters
  public bool OnlyWithImage { get; set; }
  public bool OnlyHighlighted { get; set; }

  public int PageSize { get; set; }

  public SearchQueryDescriptor()
  {
    this.Facets = new Dictionary<string, List<string>>();
    this.Page = 1;
    this.PAgeSize = 10;
  } 
}

var d = searchDescriptor;
var result = this._elasticClient.Search<SomeObject>(s =>
{
  s
   .From(d.Page * d.PageSize)
   .Take(d.PageSize)
   .Highlight(h => h
     .PreTags("<mark>")
     .PostTags("</mark>")
     .OnFields(
       f => f.OnField(a => a.Title).NumberOfFragments(0),
       f => f.OnField(a => a.Description).FragmentSize(450).BoundaryMaxSize(40)
     )
     .Encoder("html")
   );
  if (p.UseFacetting)
  {
    this.SetFacets(d, s);
    this.SetFilterFacets(d, s);
  }
  this.SetSortForSearch(d, s);
  this.CreateQuery(d, s);
  return s;
});

//normal key value facets
private void SetFacets(SearchQueryDescriptor searchDescriptor, SearchDescriptor<SomeObject> s)
{
  s.FacetTerm(t => t.OnField(f => f.CategoryId).Size(20));
  ...
}

//facet filter/query counts
private void SetFilterFacets(SearchQueryDescriptor searchDescriptor, SearchDescriptor<SomeObject> s)
{
  s.FacetFilter("hasimage", ff => ff.Term(f => f.HasImage, "true"));
 ..
}

private void CreateQuery(SearchQueryDescriptor searchDescriptor, SearchDescriptor<SomeObject> s)
{
  s.Query(q => q
    .Bool(mq => mq
      .Must(this.GenerateMustQueries(searchDescriptor, s).ToArray())
    )
  );
}

private IEnumerable<Action<QueryDescriptor<SomeObject>>> GenerateMustQueries(
  SearchQueryDescriptor searchDescriptor, SearchDescriptor<SomeObject> s
)
{
  Action<QueryDescriptor<SomeObject>> a = null;
  var query = searchDescriptor.Query;

  if (!string.IsNullOrWhiteSpace(query))
  {
    a = (q) => q
      .QueryString(qs => qs
        .OnFields(new[] { "title^3" })
        .Operator(Operator.and)
        .Query(query)
      );
    yield return a;
  }
  if (searchDescriptor.OnlyWithImage)
  {
    a = (q) => q.Term(f => f.HasImage, "true");
    yield return a;
  }
  if (searchDescriptor.OnlyHighlighted)
  {
    a = (q) => q.Term(f => f.OnlyHighlighted, "true");
    yield return a;
  }
  //selected facets
  if (searchDescriptor.Facets != null)
  {
    foreach (var f in searchDescriptor.Facets)
    {
      foreach (var v in f.Value)
      {
        var key = f.Key;
        var value = v; //C#5.0 anyone ?? 

        a = (q) => q.Term(key, value);
        yield return a;
      }
    }
  }
}

 public IEnumerable<Func<QueryDescriptor<SomeObject>, BaseQuery>> GenerateMustQueries(
        SearchQueryDescriptor searchDescriptor, 
        SearchDescriptor<SomeObject> s)
    {
        Func<QueryDescriptor<SomeObject>, BaseQuery> a = null;
    ...
    }