NHibernate large data retrieval in single query - sql-server-2005

Question

I am currently using NHibernate to read a block of 50k rows. It takes almost 20 minutes.
Data which is to be read is prepared by joining more than 5 tables in SQLSERVER 2005.
My main concern is NHibernate prepares a new query for each row retrieval, which is quite time consuming.
I know it's necessary as NHibernate has to map each row to an object, but this approach is useless where reading is main concern.
I cannot use Stateless sesstion as I am using collections to store data
I also need to apply some filter through parameters. I have also implemented Stored Procedure, but somehow it didn't help.
Is there any other way to handle large collection of data.
------Edit-------
Here are my two config file which I was using to map
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="myNameSpace" assembly="myNameSpace">
<class name="MyClass" table="TableNameFromDb">
<id name="ID" column="ID">
<generator class="native" />
</id>
<property name="prop1"/>
<property name="prop2"/>
<bag name="bag1" cascade="all-delete-orphan" inverse="false" fetch="join" lazy="false">
<key column="prop1"/>
<one-to-many class="MyClass2" />
</bag>
</class>
</hibernate-mapping>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="myNameSpace" assembly="myNameSpace">
<class name="MyClass2" table="TableNameFromDb2">
<id name="prop2" column="ID">
<generator class="native" />
</id>
<property name="prop2"/>
<property name="prop3"/>
</class>
</hibernate-mapping>
Now the main concern here is NHibernate is creating a new query for each row and sending to the database which is an overhead.

Answer 1

First of all, I think you'll have to verify what's causing the performance issue.
As Felice Pollano already mentionned, it could be that you're facing a select n+1 issue. This can possibly be solved by modifying your mapping, or, by specifying the FetchMode that must be used in the Criteria that you're using to retrieve the data.
Another thing that you should contemplate: is it really necessary to retrieve all those rows in one go? What are you trying to do? Do you really need all the data that's represented by your entities, or can you use a projection which only loads those columns that you're interested in?
Can you use Paging?
Perhaps you can use a MultiCriteria...
However, in order to solve this issue, I think more input from you is needed.

Answer 2

The problem could be due to the reason; by default, NHibernate does not fully qualify table names within its queries sent to SQL Server. To leverage sp_execsql to its fullest, requests must include fully qualified table names.
To fully qualify NHibernate queries, in app/web.config file, add the following key in NHibernate settings:
<add value="my_DB_name.dbo" key="hibernate.default_schema" />
(replace dbo as necessary.)
Try it and tell us if it gives you any performance boost?