class SuperA{}

abstract class SubA extends SuperA{}

class SubB extends SubA{
   SubC subC;
}

class SubC extends SubA{
   SubB subB;
}

<hibernate-mapping>
   <class name="SuperA" table="SuperA">
      <id column="ID" name="id" type="java.lang.Long">
         <generator class="increment" />
      </id>
      <discriminator column="DISCRIMINATOR" force="false"
         insert="true" length="30" not-null="true" type="java.lang.String" />
   </class>
</hibernate-mapping>

<hibernate-mapping>
   <subclass abstract="true" discriminator-value="SubA"
      extends="SuperA" name="SubA"
      select-before-update="false">
      <join fetch="select" table="SubA">
         <key on-delete="cascade">
            <column name="ID" />
         </key>
      </join>
   </subclass>
</hibernate-mapping>

<hibernate-mapping>
   <subclass discriminator-value="SubB"
      extends="SubA" name="SubB"
      select-before-update="false">
      <one-to-one class="SubC"
         cascade="all" name="subC" property-ref="subB" />
      <join fetch="select" table="SubB">
         <key on-delete="cascade">
            <column name="ID" />
         </key>
      </join>
   </subclass>
</hibernate-mapping>

<hibernate-mapping>
   <subclass discriminator-value="SubC"
      extends="SubA" name="SubC"
      select-before-update="false">
      <join fetch="select" table="SubC">
         <key on-delete="cascade">
            <column name="ID" />
         </key>
      </join>
      <many-to-one cascade="save-update" class="SubB"
         name="subB" not-null="true">
         <column name="SUB_B_ID" />
      </many-to-one>
   </subclass>
</hibernate-mapping>

<hibernate-mapping>
  <class name="xxx.Client" table="clients">
    <id column="id" name="id" type="int">
      <generator class="increment"/>
    </id>
    <property column="email" name="email" type="java.lang.String"/>
    <property column="name" name="name" type="java.lang.String"/>
    <property column="password" name="password" type="java.lang.String"/>
    <one-to-one cascade="all" class="xxx.ClientMainAccount" property-ref="client" name="mainAccount" />
  </class>
</hibernate-mapping>

<hibernate-mapping>
    <class discriminator-value="0" name="xxx.Account" table="accounts">
        <id column="id" name="id" type="int">
            <generator class="increment"/>
        </id>
        <discriminator column="type_id" type="integer"/>
        <property column="currency_id" name="currencyId" type="int"/>
        <property column="amount" name="amount" type="double"/>
        <subclass discriminator-value="10" name="xxx.ClientMainAccount">
            <join table="client_main_accounts">
                <key column="account_id"/>
                <many-to-one cascade="all" class="xxx.Client" column="client_id" name="client" not-null="true" />
            </join>
        </subclass>
        <subclass discriminator-value="11" name="xxx.ClientAccount">
            <join table="client_accounts">
                <key column="account_id"/>
                <many-to-one cascade="all" class="xxx.Client" column="client_id" name="client" not-null="true" />
            </join>
        </subclass>
    </class>
</hibernate-mapping>

    select
        client0_.id as id4_1_,
        client0_.email as email4_1_,
        client0_.name as name4_1_,
        client0_.password as password4_1_,
        client0_.registration_date as registra5_4_1_,
        t.id as id5_0_,
        t.currency_id as currency3_5_0_,
        t.amount as amount5_0_,
        t.client_id as client2_6_0_
    from
        clients client0_
    left outer join
    (
   select * from
      accounts clientmain1_
   left outer join
      client_main_accounts clientmain1_1_
        on clientmain1_.id=clientmain1_1_.account_id
        where clientmain1_.type_id=10
    ) t
     on client0_.id=t.client_id

    where
        client0_.id=1