NHibernate Return collection and single object

return collection

public class ExtendedShopAccountProvider : ShopAccountProvider
   {
       //3.4. LOGIN WITH ERP NUMBER
       /// <summary>
       /// This method will get Shop Accounts by Account Id.
       /// </summary>
       /// <param name="accountId"></param>
       /// <returns></returns>  
       public virtual IShopAccountCollection GetShopAccountsByAccountId(string accountId)
       {
           Guard.ThrowIfEmptyString(accountId, "accountId", "AccountId cannot be empty.");
 
           var result = WrapDataAccessException(() =>
           {
               using (var sm = CreateSessionManager(true))
               {
                   var criteria = sm.Session.CreateCriteria(GetRegisteredType<IShopAccount>());
                   criteria.Add(Expression.Eq("ReferenceId", accountId));
                   criteria.Add(Expression.Eq("Activated", true));
                   criteria.Add(Expression.Eq("ShopAccountType", ShopAccountType.Customer));
                   criteria.Add(Expression.Eq("WebsiteId", Context.WebsiteId));
 
                   var countCriteria = CriteriaTransformer.TransformToRowCount(criteria);
                   int totalCount = countCriteria.UniqueResult<int>();
 
                   var results = criteria.List<IShopAccount>();
                   var collection = ObjectFactory.Create<IShopAccountCollection>();
                   collection.Initialize(results, totalCount);
                   return collection;
               }
           }, "Cannot get the list of shop accounts.");                         
           return result;
 
       }

single

public virtual IShopAccount GetShopAccountByEmail(string email)
        {
            Guard.ThrowIfEmptyString(email, "email", "Email cannot be empty.");

            return WrapDataAccessException(() =>
            {
                using (var sm = CreateSessionManager(true))
                {
                    var criteria = sm.Session.CreateCriteria(GetRegisteredType<IShopAccount>());
                    criteria.Add(Expression.Eq("Email", email));
                    criteria.Add(Expression.Eq("WebsiteId", Context.WebsiteId));
                    return criteria.UniqueResult<IShopAccount>();
                }
            }, "Cannot get shop account by email: Email = {0}, WebsiteId = {1}.",
            email, Context.WebsiteId);
        }

Pass String List and get List Object 

public virtual IList<IProductEnrichment> GetProductEnrichments(IList<string> productIds)
        {
            if (productIds.Count == 0)
                return new List<IProductEnrichment>();

            return WrapDataAccessException(() =>
            {
                using (var sm = CreateSessionManager(true))
                {
                    var criteria = sm.Session.CreateCriteria(GetRegisteredType<IProductEnrichment>())
                        .Add(Restrictions.Eq("WebsiteId", Context.WebsiteId));

                    var collection = GetListByPortions(criteria, "ProductId", productIds);
                    return collection.Cast<IProductEnrichment>().ToList();
                }
            }, "Cannot get products enrichments for products with IDs = {0} and website = {1}.", productIds.JoinWith(", "), Context.WebsiteId);
        }

Get List

/// Ticket 88704: [Kavo] 3.9. PDP – RELATED ITEMS
        /// <summary>
        /// Get related product sets
        /// </summary>
        /// <returns>List of related product items</returns>
        public IList<IRelatedProductSet> GetRelatedProductSets()
        {
            return WrapDataAccessException(() =>
            {
                using (var sm = CreateSessionManager(true))
                {
                    var criteria = sm.Session.CreateCriteria(GetRegisteredType<IRelatedProductSet>());
                    criteria.Add(Expression.Eq("WebsiteId", Context.WebsiteId));
                    return criteria.List<IRelatedProductSet>();
                }
            }, "Cannot get related product sets: WebsiteId = {0}.", Context.WebsiteId);
        }

Update/Save object

/// Ticket 88704: [Kavo] 3.9. PDP – RELATED ITEMS
        /// <summary>
        /// Save/Update related product set
        /// </summary>
        /// <param name="relatedProductSet">related product set object</param>
        public void UpdateRelatedProductSet(IRelatedProductSet relatedProductSet)
        {
            WrapDataAccessException(() =>
            {
                using (var sm = CreateSessionManager(false))
                {
                    sm.Session.Merge(relatedProductSet);
                    sm.Commit();
                }
            }, "Cannot update related product sets: Id = {0}, CategoryId = {1}, WebsiteId = {2}.",
           relatedProductSet.Id, relatedProductSet.CategoryId, relatedProductSet.WebsiteId);
        }

Filter by table element.

/// Ticket 88704: [Kavo] 3.9. PDP – RELATED ITEMS
        /// <summary>
        /// Get related product set
        /// </summary>
        /// <param name="categoryId">category id</param>
        /// <returns>related product set</returns>
        public IRelatedProductSet GetRelatedProductSetByCategoryId(string categoryId)
        {
            return WrapDataAccessException(() =>
            {
                using (var sm = CreateSessionManager(true))
                {
                    var criteria = sm.Session.CreateCriteria(GetRegisteredType<IRelatedProductSet>());
                    criteria.Add(Expression.Eq("WebsiteId", Context.WebsiteId));                   
                    criteria.Add(Expression.Eq("CategoryId", categoryId));                   
 
                    return criteria.UniqueResult<IRelatedProductSet>();
                }
            }, "Cannot get related products set: CategoryId = {0}, WebsiteId = {1}.", categoryId, Context.WebsiteId);
        }

IN operator 

/// Ticket 88704: [Kavo] 3.9. PDP – RELATED ITEMS
/// <summary>
/// Get related product items by category ids.
/// </summary>
 /// <param name="categoryId">category id</param>
 /// <returns>related product item</returns>
 public IList<IRelatedProductSet> GetRelatedProductSetsByCategoryIds(List<string> categoryIds)
  {
      if (categoryIds.Count == 0)
          return new List<IRelatedProductSet>();

         return WrapDataAccessException(() =>
         {
             using (var sm = CreateSessionManager(true))
             {
                    var criteria = sm.Session.CreateCriteria(GetRegisteredType<IRelatedProductSet>())
                       .Add(Restrictions.Eq("WebsiteId", Context.WebsiteId))
                       .Add(Expression.In("CategoryId", categoryIds));   <----------                  
                    return criteria.List<IRelatedProductSet>();                     

             }
         }, "Cannot get related products set for products with Ids = {0} and website = {1}.", categoryIds.JoinWith(", "), Context.WebsiteId);
                       
 }