1

MDE using Hibernate ORM

Leonardo Passos(lpassos@gsd.uwaterloo.ca)

2

Object Relational Mapping (ORM)

3

ORM library in Java

4

What is a mapping?

● Hibernate's MDE support:● Generation of corresponding DDL scripts● Generation of Java POJOs

<hibernate-mapping> <class name="sample.Person" table="person"> <id name="id"> <generator class="native"/> </id> <property name="name" type="string" not-null="true"/> <property name="phoneNumber" type="string" not-null="true"/> <property name="email" type="string" not-null="true"/> </class></hibernate-mapping>

5

Associations

● One to one

● One to many

● Many to many

● Unidirectional/Bidirectional

6

Some examples...

7

Unidirectional one to one association

<hibernate-mapping> <class name="sample.Person" table="person"> <id name="id"> <generator class="native"/> </id> <property name="name" type="string" not-null="true"/> <property name="phoneNumber" column=”phone_number” type="string" not-null="true"/> <property name="email" type="string" not-null="true"/>

<many-to-one name="address" class="Address" column="address_id" cascade="save-update" unique="true"/> </class></hibernate-mapping>

Needs mapping definition

Solution: foreign key association

8

Unidirectional one to one association

<hibernate-mapping> <class name="sample.Address" table="address"> <id name="id"> <generator class="native"/> </id> <property name="street" type="string" not-null="true"/> <property name="zipcode" type="string" not-null="true"/> <!-- other properties of interest... --> </class></hibernate-mapping>

9

Unidirectional one to one association (stronger)

<hibernate-mapping> <class name="sample.Person" table="person"> <id name="id"> <generator class="native"/> </id> <property name="name" type="string" not-null="true"/> <property name="phoneNumber" column=”phone_number” type="string" not-null="true"/> <property name="email" type="string" not-null="true"/>

<many-to-one name="address" class="Address" column="address_id" cascade="all" unique="true"/> </class></hibernate-mapping>

10

Bidirectional one to one association

● Person defined as before, but Address now contains

<hibernate-mapping> <class name="sample.Address" table="address"> <id name="id"> <generator class="native"/> </id> <property name="street" type="string" not-null="true"/> <property name="zipcode" type="string" not-null="true"/> <!-- other properties of interest... --> <one-to-one name="person" class="sample.Person" property-ref="address"/> </class></hibernate-mapping>

11

Bidirectional one to one association(alternative solution)

<hibernate-mapping> <class name="sample.Person" table="person"> <id name="id"> <generator class="native"/> </id> <!-- properties... --> <one-to-one name="address" class="sample.Address" cascade="all" /> </class></hibernate-mapping>

<hibernate-mapping> <class name="sample.Address" table="address"> <id name="id"> <generator class="foreign"> <param name=”property”> person </param> </id> <!-- properties... --> <one-to-one name=”person” class=”sample.Person” constrained=”true”/> </class></hibernate-mapping>

Solution: primary key association

12

Bidirectional many to many association

● Suppose two classes: Category and Item● A bidirectional association from Category to Item ('*' on both ends)

– In RDB, one needs to use an intermediate table to connect category and item(e.g.: category_item)

<hibernate-mapping> <class name="sample.Category" table="category"> ... <set name="items" table="category_item" lazy="true" cascade="save-update"/> <key column="category_id"/> <many-to-many class="Item" column="item_id"/> </set> </class></hibernate-mapping>

1

13

Bidirectional many to many association

● Suppose two classes: Category and Item● A bidirectional association from Category to Item ('*' on both ends)

– In RDB, one needs to use an intermediate table to connect category and item(e.g.: category_item)

<hibernate-mapping> <class name="sample.Item" table="item"> ... <set name="categories" table="category_item" lazy="true" cascade="save-update inverse=”true”"/> <key column="item_id"/> <many-to-many class="Category" column="category_id"/> </set> </class></hibernate-mapping>

2

14

Conclusions

15

Conclusions

● The semantics of associations are defined as part of the mapping specification● Users give the semantics they need

● Models are written in a declarative-fashion using XML

● MDE Support:● DDL generation

● POJO generation

16

Questions