Question

I have two lists comprised of different complex-objects, and each one is from 2 separate data-sources. One list may-or-may-not contain records. When any records exist in the “optional” list I need the “normal” list to be further-filtered.

Unfortunately, I can only find very simple examples here and online, which is why I am asking this question.

The Pseudo-Logic Goes Like This:
When QuickFindMaterial records exist, get all DataSource records where query.Name is in the QuickFindMaterial.Material collection. If no QuickFindMaterial records exist do not affect the final result. Lastly, select all distinct DataSourcerecords.

The Classes Looks Like:

public class QuickFindMaterial
{
    public string SiteId { get; set; }
    public string Material { get; set; }
}

The Code Looks Like:
I have commented-out my failed WHERE logic below

    var dataSource = DocumentCollectionService.ListQuickFind();
    var quickFindMaterial = ListMaterialBySiteID(customerSiteId);

    var distinct = (from query in dataSource
                                    select new
                                               {
                                                   ID = query.DocumentID,
                                                   Library = query.DocumentLibrary,
                                                   ModifiedDate = query.DocumentModifiedDate,
                                                   Name = query.DocumentName,
                                                   Title = query.DocumentTitle,
                                                   Type = query.DocumentType,
                                                   Url = query.DocumentUrl,
                                               })
//.Where(x => x.Name.Contains(quickFindMaterial.SelectMany(q => q.Material)))
//.Where(x => quickFindMaterial.Contains(x.Name))
.Distinct();

Answer 1

I think this is what you want:

.Where(x => !quickFindMaterial.Any() || quickFindMaterial.Any(y => x.Name == y.Material))