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Flexible Hibernate Named Query Mapping

I'm using multiple hibernate named queries that maps to the same hibernate class.
The problem is because the different named queries return different attributes, and not all the attributes I'm getting an "invalid column" error. The way to resolve it is to make sure the queries map all the attributes defined by the hibernate class. (Hibernate native query : Invalid Column Name Error SQL-17006)
Here's an sample of what I have:
<hibernate-mapping>
<class name="com.company.ObjectA" mutable="false" >
<id name="id" type="string"/>
<property name="prop1" type="string"/>
<property name="prop2" type="string"/>
</class>
<sql-query name="get1">
<return alias="a" class="com.company.ObjectA"/>
<![CDATA[
select
id as {a.id},
prop1 as {a.prop1}
from TABLE_A
]]>
</sql-query>
<sql-query name="get2">
<return alias="a" class="com.company.ObjectA"/>
<![CDATA[
select
id as {a.id},
prop2 as {a.prop2}
from TABLE_A
]]>
</sql-query>
</hibernate-mapping>
I have defined a temporary fix where the queries return empty values to make sure all hibernate class attributes are mapped:
<sql-query name="get2">
<return alias="a" class="com.company.ObjectA"/>
<![CDATA[
select
id as {a.id},
'' as {a.prop1},
prop2 as {a.prop2}
from TABLE_A
]]>
</sql-query>
But that is not ideal, because for my real case, I have quite a few of these unmapped attributes, and more named queries that use a different combination of attributes in the hibernate class.
Is there another way to resolve it? Also I need it to return data to the same object 'ObjectA', because of it's integration with the rest of the code.

How do I avoid the query calling associated objects

I am sure there is a hibernate term for this but I am not sure what it is (and I could therefore probably look up the answer) but here goes.
I have a Product Pojo where one of the fields is a Set of Suppliers (also a Pojo). When I call to get a list of Products, by default it queries to get the list of Suppliers- which is what I would expect.
However, sometimes I do not require the data in the Set and the querying it is taking too long to just bear it. Is there a way to sometimes avoid querying the data for the Set?
Or is my design incorrect?
My Product.hbm.xml mapping file has:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping default-access="field" default-lazy="false" package="model">
<class name="model.Product" table="PRODUCT">
<id column="PRODUCT_ID" name="id" type="long">
<generator class="native" />
</id>
...
<set name="suppliers" sort="unsorted" table="SUPPLIERS">
<key column="PRODUCT_ID" />
<one-to-many class="model.Suppliers" />
</set>
...
</class>
</hibernate-mapping>

The default behavior of Hibernate is what you are expecting: All collections mapped for an entity, and all associated entities, be it through to-many or to-one associations, are not loaded by default.
But if you have defined the lazy="false" for the Set of Suppliers, Hibernate will fetch the associated collection eagerly along with the Product.
Change the suppliers mapping as below, so that Hibernate will not fetch it eagerly:
<set name="suppliers" sort="unsorted" table="SUPPLIERS" lazy="true">
<key column="PRODUCT_ID" />
<one-to-many class="model.Suppliers" />
</set>
EDIT:
The above mapping is the default fetching strategy for suppliers. Now if you want to load suppliers along with the Product, you can override this default strategy at runtime in code:
String productSelect = "select p from Product "
+ "p left join fetch p.suppliers "
+ "where p.productName=:pname";
Query query = session.createQuery(productSelect);
query.setParameter("pname", productname);
Product result = (Product) query.uniqueResult();
The above query will fetch the Product along with the set of suppliers. So, wherever needed, you can override the default strategy by using above query to get suppliers along with Product.

Set the fetchtype to LAZY (instead of EAGER) for the supplier Set.

Not null key while doing insert using hibernate

I am new to Hibernate and was writing some test program.
I am wondering if its a must to have a table , one column of which will be updated using some kind of sequence.
For ex. I created a table
create table course(course_name varchar2(20));
and when I am defining Course.hbm.xml in the following way
<class name="Course" table="COURSE" >
<property name="course">
<column name="course"/>
</property>
</class>
I am getting an error in the XML file saying a declaration of "id" or something similar is expected. I can give the whole error message if required.

You need an ID column so hibernate can identify that row in the table. I'm not fluent in that oldschool hibernate xml mapping but it should look roughly like that:
create table course(id integer primary key, course_name varchar2(20));
<class name="Course" table="COURSE" >
<id name="id">
<!-- uses sequence, auto increment or whatever your DBMS uses for id generation -->
<generator class="native"/>
</id>
<property name="course">
<column name="course"/>
</property>
</class>
As a side note: mapping your entities with annotations is a bit more common nowadays. Makes it easier, especially for starters.

Map query results to property

Is there way to set results of a query to java DTO property using hibernate ?
Something like,
<hibernate-mapping>
<class name="myDTO" table="my_table">
<property name="myProperty" query="what_i_need" />
</class>
<query name="what_i_need">
<![CDATA[
from .....
]]>
</query>
</hibernate-mapping>
I'm using spring, hibernate, java.

If I understand you correctly #josef-prochazka 's suggestion of using a formula would be what you need.
See also:
http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/mapping.html#mapping-column
http://www.onjava.com/pub/a/onjava/2005/08/03/hibernate.html?page=2
http://www.java2s.com/Code/Java/Hibernate/ColumnFormulaStringConcatenate.htm

How do you pass parameters to Hibernate's subselect tag?

The example at the end of hibernate section 5.1.3 does not show an example on passing parameters.
There is no difference between a view
and a base table for a Hibernate
mapping. This is transparent at the
database level, although some DBMS do
not support views properly, especially
with updates. Sometimes you want to
use a view, but you cannot create one
in the database (i.e. with a legacy
schema). In this case, you can map an
immutable and read-only entity to a
given SQL subselect expression:
<class name="Summary">
<subselect>
select item.name, max(bid.amount), count(*)
from item
join bid on bid.item_id = item.id
group by item.name
</subselect>
<synchronize table="item"/>
<synchronize table="bid"/>
<id name="name"/>
...
</class>
Is it possible? And if so, how?
Thanks,
Franz

I don't think that it is possible, because the mapping file is like a static description.

Since Hibernate 3 you can use formulas to map this types of readonly calculated fields. Example:
#Formula("(SELECT b.BANK_NAME FROM " +
" BANK_INFORMATION b, BILLING_AGENT_BANK ba " +
" WHERE ba.CNPJ = COMPANY_CNPJ " +
" AND b.BANK_ID = ba.BANK_ID)")
public String getBankName() {
return bankName;
}
This example is with a Annotated property, but you can do the same in the mapping file.

In NHibernate:
<class name="Blog" mutable="false">
<subselect>
SELECT Blog.Id, Blog.Author, Blog.Title, Comment.Comment
FROM Blog INNER JOIN Comment ON Blog.Id = Comment.Blog_id
WHERE Comment.LanguageId = :blogcomment.languageId
</subselect>
<id name="Id">
<generator class="assigned" />
</id>
<property name="Author" />
<property name="Title" />
<property name="Comment" />