I have a class Person, which is associated with Person many-to-many associaton,
<hibernate-mapping>
<class
name="src.model.Person"
table="PERSONS"
>
.
.
.
<set
name="friends"
table="FRIENDS_PERSON"
lazy="true"
cascade="all"
sort="unsorted"
>

<key
column="HAVE_A_FRIEND"
>
</key>

<many-to-many
class="src.model.Person"
column="IS_A_FRIEND"
outer-join="auto"
/>

</set>
</hibernate-mapping>

I need to write a query which will check if given two person are friends. In native SQL this query would be something like this.

SELECT COUNT(*) FROM FRIENDS_PERSON WHERE have_a_friend=:id1 AND is_a_friend=:id2");

How to write it in Hibernate, or how to use this query as a native sql query in hibernate?

the native sql version is only possible in hibernate3 since it supports scalar return values.

examples for this are in the docs.

i have Hibernate3

in docs there are very simple examples. I cant find there how to retrieve values from tables which don't have counterparts in class model (such as in my above problem. I don't have class FriendPerson, and i need to execute some query on this table.

eh ? your native sql does not need to refer to any entity...just map the return value as a <return-scalar> in hbm.xml or addScalar() in API.

its in the docs.