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understanding hibernate mapping tutorial

Here i have attached a hibernate Event.hbm.xml file.

I have a query here .

note , we have an entry
<id name="id" column="uid" type="long" unsaved-value="null">

and also we have entry...

<set name="speakers" cascade="all">
<key column="event_id"/>
<one-to-many class="Speaker"/>
</set>

does that mean hibernate will automatically understand "id" column in Event table is a foreign key "event_id" column in Speaker table ?

How hibernate will understand that ?i don't see any foreign key tag in the mapping file ....so i am bit confused at this part.

I am not sure , how hibernate will relate these two column . because i think whenever a value say "1" is saved in "id" field , there will also "1" be saved in event_id column because of this mapping file....right ?

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
 
<hibernate-mapping>
    <class name="Event" table="events">
        <id name="id" column="uid" type="long" unsaved-value="null">
            <generator class="increment"/>
        </id>
        <property name="name" type="string" length="100"/>
        <property name="startDate" column="start_date"
                  type="date"/>
        <property name="duration" type="integer"/>
        <many-to-one name="location" column="location_id" class="Location"/>
        <set name="speakers" cascade="all">
            <key column="event_id"/>
            <one-to-many class="Speaker"/>
        </set>
        <set name="attendees" cascade="all">
            <key column="event_id"/>
            <one-to-many class="Attendee"/>
        </set>
    </class>
</hibernate-mapping>

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Mick Barry

>

that specifies which column is the foreign key for a Speaker
And as it is specified in the Event mapping then it relates to the Event class

cofactor

ASKER

the DDL has been given as below in the tutorial

create table events (uid int ,
name varchar,
start_date date,
duration integer,
location_id int)

create table speakers (uid int,
firstName varchar,
lastName varchar,
event_id int)

but there is no FK constraint put in this DDL .....shall we need to put constraints here ?

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Mick Barry

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