Question

I have a user and a message table. User to Message are one-to-many relationships and Message to User are many-to-one relationships. I’ve marked one of the many-to-one as fetch join. When I ‘get’ a single Message, Hibernate runs a join query, but when I fetch all the messages, Hibernate runs select queries instead of a join. What could be the reason? Following are the details:

Relationship between them:

User

<set name="messagesForFromUserUid" lazy="true" table="message" inverse="true" cascade="save-update">
        <key>
            <column name="from_user_uid" not-null="true" />
        </key>
        <one-to-many class="repository.Message" />
    </set>
    <set name="messagesForToUserUid" lazy="true" table="message" fetch="select">
        <key>
            <column name="to_user_uid" not-null="true" />
        </key>
        <one-to-many class="repository.Message" />
    </set>

Message

<many-to-one name="userByFromUserUid" class="repository.User" fetch="join" lazy="false">
        <column name="from_user_uid" not-null="true" />
    </many-to-one>
    <many-to-one name="userByToUserUid" class="repository.User" fetch="select" lazy="proxy">
        <column name="to_user_uid" not-null="true" />
    </many-to-one>

When I fetch a single message object, Hibernate runs one join query as expected:

Message m = (Message) s.get(Message.class, 2);

Hibernate: 
select
    message0_.message_uid as message1_1_1_,
    message0_.from_user_uid as from2_1_1_,
    message0_.to_user_uid as to3_1_1_,
    message0_.message_text as message4_1_1_,
    message0_.created_dt as created5_1_1_,
    user1_.user_uid as user1_0_0_,
    user1_.user_name as user2_0_0_,
    user1_.user_password as user3_0_0_,
    user1_.email as email0_0_,
    user1_.first_name as first5_0_0_,
    user1_.last_name as last6_0_0_,
    user1_.created_dt as created7_0_0_ 
from
    hello.message message0_ 
inner join
    hello.user user1_ 
        on message0_.from_user_uid=user1_.user_uid 
where
    message0_.message_uid=?

But when I fetch all the messages in one go, Hibernate runs select queries instead:

List<Message> l = s.createQuery("from Message").list();

Hibernate: 
select
    message0_.message_uid as message1_1_,
    message0_.from_user_uid as from2_1_,
    message0_.to_user_uid as to3_1_,
    message0_.message_text as message4_1_,
    message0_.created_dt as created5_1_ 
from
    hello.message message0_
Hibernate: 
select
    user0_.user_uid as user1_0_0_,
    user0_.user_name as user2_0_0_,
    user0_.user_password as user3_0_0_,
    user0_.email as email0_0_,
    user0_.first_name as first5_0_0_,
    user0_.last_name as last6_0_0_,
    user0_.created_dt as created7_0_0_ 
from
    hello.user user0_ 
where
    user0_.user_uid=?

Hibernate: 
select
    user0_.user_uid as user1_0_0_,
    user0_.user_name as user2_0_0_,
    user0_.user_password as user3_0_0_,
    user0_.email as email0_0_,
    user0_.first_name as first5_0_0_,
    user0_.last_name as last6_0_0_,
    user0_.created_dt as created7_0_0_ 
from
    hello.user user0_ 
where
    user0_.user_uid=?

Answer 1

Looks like Hibernate does not always use fetch strategies defined in the mapping, for HQL or Criteria queries. They are typically used for get/load. Found a reference here: https://forum.hibernate.org/viewtopic.php?f=1&t=957561