internal class DocumentPermissionsHelper
{
    private readonly CustomerModelContext dc;
    public GroupPermissionsHelper(CustomerModelContext dc) { this.dc = dc; }

    public IQueryable<Document> SelectDocumentsAccessibleToUser(IQueryable<Document> query, Guid userId)
    {
        var permissionsQuery = dc. ... // really big query with multiple JOIN's to determine which user has access to which documents
        IQueriable<Guid> docIdsAccessibleToUserQuery =
            from permissions in permissionsQuery.Where(_ => _.UserId == userId && _.AccessLevel == "Read")
            select permissions.DocumentId;

        return from accessibleDocId in docIdsAccessibleToUserQuery.Distinct()
                from accessibleDoc in query.Where(g => g.Id == accessibleDocId)
                select accessibleDoc;
    }
}

public void GetLatestDocsCount(Guid currentUserId)
{
    using (var dc = new MyDbContext(_environment))
    {
        var helper = new DocumentPermissionsHelper(dc);
        var docQuery = dc.Docs.Where(d => d.CreatedDate > DateTime.Now.AddDays(-1));
        docQuery = helper.SelectDocumentsAccessibleToUser(docQuery, userId);
        int latestDocsCount = docQuery.Count();
        return latestDocsCount;
    }
}