Question

I am trying to filter displayed documents in a winforms app using a checked list box, so that when 2 tags are selected only documents containing those tags would show up and be further winnowed down when a third tag was selected. I am using Entity Framework. Here is what I have but I think it might not be efficient. I don’t like that I have to query the db so often. Any thoughts?

List<int> docIds = null;
        if (tags != null)
        {
            docIds.AddRange(from di in frmFocus._context.AllocateDocumentTags
                            where di.tagId == tags[0]
                            select di.documentId);
            for (int i = 1; i < tags.Length; i++)
            {
                List<int> docList = (from dId in frmFocus._context.AllocateDocumentTags
                                     where dId.tagId == tags[i]
                                     select dId.documentId).ToList();
                foreach (int n in docIds)
                {
                    if (!docList.Contains(n))
                    {
                        docIds.Remove(n);
                    }
                }
            }

        }

---

Now I am trying to display the docs based on the ids but… here’s the new code

docIds = (from di in frmFocus._context.AllocateDocumentTags.Distinct()
                                    where tags.Contains(di.tagId)
                                    select di.documentId).ToList();
                tagManagment.fillUsed(docIds);
            }
            ObjectSet<Documents> _docs = (from d in frmFocus._context.Documents
                     where docIds.Contains(d.id)
                     select d);

Answer 1

You can basically just do a contains on tags:

List<int> docIds = (from di in frmFocus._context.AllocateDocumentTags
                    where tags.Contains(di.tagId)
                    select di.documentId);

For the JOIN:

ObjectSet<Documents> _docs = (from doc in docIds
                              join d in frmFocus._context.Documents.ToList()  on doc equals d.id
                              select d);