Objective:
Implement Many
to Many Relation in Liferay development using service builder tool.
In our real time development we come across Many to Many relation mapping when we
interact with data base.
Hibernate Object relational mapping support one to many and many to many relations. Coming to liferay we never directly implement
hibernate in liferay development and we just use service builder tool so that we can generate
all data base services with minimal effort.
Liferay service builder support many to many
relation in liferay.
Scenario
A student can have many courses and course can be
taken by many students
Introduction:
Liferay have very good tool called service builder
from which we can build required services for portlet. Services are nothing but
database interaction related java classes, interfaces and its configuration
files. Service builder uses spring and hibernate to build service layer for
portlet.
To build service layer for portlet service builder
need one configuration file called service.xml
by using this it will get information to generate required service classes and
interfaces.
We already aware of spring and hibernate integration
in normal web applications. Same way service builder build model/POJO classes, DAO
classes and service classes.
Along with java classes some spring configuration
files and Hibernate mapping files will be generated.
Spring will be load all required services in
application context so that we can use required methods from some Util classes
The
following are the classes and interface for each entity which we defined in service.xml
XXXModel
XXXModelmpl
XXXPersistence
XXXPersistenceImpl
XXXServiceImpl
XXXLocalServiceImpl
XXXServiceUtil
XXXLocalServiceUtil
XXXUtil
Here XXX is Entity Name
Note:
In
service builder each table will be referred as Entity
In
Development we will use only Util classes to do database interaction
|
Many
to Many Implementation in Liferay
Service builder can support Many to Many Relation so that we can use this functionality in real
time development
In the service builder we will define entities and
its columns in service.xml
file from this information Service Builder
generated the required services to each entity. These services will be
interacted with data base tables.
Liferay providing mapping-table attribute for column from this we can achieve many to
many relation between tables
What are the tables or entities which are participated
in many to many relations, for those tables we have to define column and that
column should have mapping-table
attribute and entity attributes.
What are the column which contains mapping-table those columns are really/physically
not existed in the database tables, the column are virtual columns for entity
which will support many to many relation between table
When we use Many to Many Relation between tables we will
use mapping –table attribute for the
column. Whatever the value we provided to mapping-table
attribute then service builder create another new tables with that value.
The created table will have two columns and those
columns are representing each table primary keys i.e. the tables participated in May
to Many Relation.
Concept
Example:
Assume we have Student
and Course tables. When we implement
Many to Many relation between these
tables we will get new table called Students_Courses
and the table contains two columns and the columns are primary keys of Student and Course
This Student_Courses
is the value of mapping-table attribute
in entity column.
Example
of service.xml
<service-builder package-path="com.meera.db">
<author>E5410</author>
<namespace>meera</namespace>
<entity name="Student" local-service="true" remote-service="true"
cache-enabled="false">
<column name="studentId" type="long" primary="true"
/>
<column name="studentName"
type="String" />
<column name="studentPlace"
type="String" />
<column name="studentCollege"
type="String" />
<column
name="courses" type="Collection" entity="Course"
mapping-table="Students_Courses"/>
</entity>
<entity name="Course" local-service="true" remote-service="true"
cache-enabled="false">
<column name="courseId" type="long" primary="true"
/>
<column name="courseName"
type="String" />
<column name="courseGroup"
type="String" />
<column
name="students" type="Collection" entity="Student"
mapping-table="Students_Courses" />
</entity>
</service-builder>
|
The following table will be created in data base
create table meera_Course (
courseId
LONG not null primary key,
courseName VARCHAR(75) null,
courseGroup VARCHAR(75) null
);
create table meera_Student (
studentId
LONG not null primary key,
studentName VARCHAR(75) null,
studentPlace VARCHAR(75) null,
studentCollege VARCHAR(75) null
);
create table meera_Students_Courses (
courseId
LONG not null,
studentId
LONG not null,
primary key (courseId,
studentId)
);
|
Note:
Liferay service builder created tables and the table
names appended with name space.
Observation:
- The columns which contains mapping-table attribute those column really not presented in table’s SQL as columns.
- In service.xml we have defined only 2 tables but service builder created another tables and the table name i.e. we have provided value for mapping-table attribute in the column.
- The mapping table has two columns these columns represents primary keys of other tables which are participated in many to many relation.
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