Mapping dilemma

biguniverse · **Joined:** Fri Jul 29, 2005 2:11 pm **Posts:** 21

Hello. I have one parent table, one child table and 3 reference/lookup tables (see diagram below).

What is a good to set the Parent object in Hibernate (i.e. mapping)? I'll be doing basic CRUD operations on the Parent object.

Also, would you use createQuery/HQL at all like it is demonstrated in the Weblog example in the Hibernate 3 reference guide?

pksiv · **Posted:** Tue Aug 09, 2005 4:13 pm

biguniverse wrote:

Hello. I have one parent table, one child table and 3 reference/lookup tables (see diagram below).

What is a good to set the Parent object in Hibernate (i.e. mapping)? I'll be doing basic CRUD operations on the Parent object.

Also, would you use createQuery/HQL at all like it is demonstrated in the Weblog example in the Hibernate 3 reference guide?

I would map the reference objects as <many-to-one>'s and use the Criteria API since this is a very simple/straightforward model.

biguniverse · **Joined:** Fri Jul 29, 2005 2:11 pm **Posts:** 21

Thanks.

How would you map the Parent/Child (1...0.*) relationship?

Perhaps, the parent having a <bag> for it's children and the Child having <many-to-one> mapping back to the parent (i.e. bi-directional)?

pksiv · **Posted:** Tue Aug 09, 2005 4:26 pm

biguniverse wrote:

Thanks.

How would you map the Parent/Child (1...0.*) relationship?

Perhaps, the parent having a <bag> for it's children and the Child having <many-to-one> mapping back to the parent (i.e. bi-directional)?

The documentation indicates that Bags give good performance and do mention it in several examples so I don't think you could go wrong with that choice.

christian · **Posted:** Tue Aug 09, 2005 4:31 pm

Actually, the documentation says that <bag> is a pretty bad choice.

pksiv · **Posted:** Tue Aug 09, 2005 4:35 pm

christian wrote:

Actually, the documentation says that <bag> is a pretty bad choice.

Christian,

I'm certainly not going to disagree with you but I gave that advice based on Section 20.5.3 Bags and Lists are the most efficient inverse collections.

The example provided in this section seems to exactly mimic his example.

biguniverse · **Joined:** Fri Jul 29, 2005 2:11 pm **Posts:** 21

Thanks, Preston.

1. Christian, how would you map this, if <bag> is a bad choice?

I too had the impression that <bag> wasn't a bad choice based on the hibernate reference.

2. Also, is using createQuery with HQL as demonstrated in the Weblog sample application (also, in hibernate 3 reference), a good design? If you just need all rows back, won't the mapping (with lazy=false) automatically load the Child collection in my Parent class?

christian · **Posted:** Tue Aug 09, 2005 5:21 pm

I said <bag>, not Bag. Please read the "Performance" chapter again.

Basilio · **Posted:** Tue Aug 09, 2005 8:13 pm

I would do that with Set it performs pretty well

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
                            "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
                            "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<hibernate-mapping package="model">

    <class name="Parent" table="PARENT">
        <id name="parentId" column="PARENTID" type="java.lang.Integer">
            <generator class="native"/>
        </id>
 
        <property name=".." column="...." type="java.lang.String" />
        
      <set 
         name="children"          cascade="all-delete-orphan" inverse="true" >
          <key column="PARENT_ID"/>
          <one-to-many class="Parent"/>
      </set>  
      
    </class>
    
</hibernate-mapping>

on child maps define many-to-one relationship to parent

biguniverse · **Joined:** Fri Jul 29, 2005 2:11 pm **Posts:** 21

Thanks.

And, for the reference objects, as Preston (above) suggested, would you also go with as <many-to-one>'s with use the Criteria API?

Basilio · **Posted:** Wed Aug 10, 2005 12:42 am

biguniverse wrote:

Thanks.

And, for the reference objects, as Preston (above) suggested, would you also go with as <many-to-one>'s with use the Criteria API?

I will and I do. In our application we have only few places where we are using HQL and probably we will convert them to Criteria later. All of the rest is built with Criteria API. Suggested mapping actually works perfectly for us. Your case is kind of standard in our app. Approx 80 % of our classes have exactly the same model like yours: parent/child plus lots of refereces mapped with many-to-one.

biguniverse · **Joined:** Fri Jul 29, 2005 2:11 pm **Posts:** 21

Thanks. By the way, if you have a sample XML file that shows "parent/child plus lots of refereces mapped with many-to-one", that would be awesome :-)

Thanks again.

Basilio · **Posted:** Wed Aug 10, 2005 2:54 pm

biguniverse wrote:

Thanks. By the way, if you have a sample XML file that shows "parent/child plus lots of refereces mapped with many-to-one", that would be awesome :-)

Thanks again.

You are welcome

It is a simplified mapping:

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
                            "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
                            "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<hibernate-mapping package="model.data">

   <class name="Customer" table="CUSTOMER">
      <id name="customerId" column="CUSTOMER_ID"
         type="java.lang.Integer">
         <generator class="native" />
      </id>

      <property name="firstName" column="FIRST_NAME" type="java.lang.String" />
      <property name="lastName" column="LAST_NAME" type="java.lang.String" />
      <property name="middleName" column="MIDDLE_NAME" type="java.lang.String" />
            
      <many-to-one name="nameSuffix" column="NM_SFX_SCODE_ID" class="model.Systemcode" />
      <many-to-one name="namePrefix" column="NM_PFX_SCODE_ID" class="model.Systemcode" />
      <many-to-one name="maritalStatus" column="MRTL_STS_SCODE_ID" class="model.Systemcode" />
      <many-to-one name="language" column="LANGUAGE_ID" class="model.Language" />
      <many-to-one name="customerStatus" column="STATUS_CODE_ID" class="model.Systemcode" />

      <set name="phones" lazy="true"
         cascade="all-delete-orphan" inverse="true">
         <key column="CUSTOMER_ID" />
         <one-to-many class="Phone" />
      </set>

      <set name="addresses" lazy="true"
         cascade="all-delete-orphan" inverse="true">
         <key column="CUSTOMER_ID" />
         <one-to-many class="Address" />
      </set>

   </class>

</hibernate-mapping>

All many-to-one to referencial classes are unidirectional