Objective:
Implement Many to Many Relation in liferay
development using service builder tool.
Implantation
in Portlet Development
The
following are steps to implement in portlet development
- Create
simple Liferay MVC portlet using Liferay IDE in eclipse
- Create
Service.xml file in Portlet WEB-INF directory
- Define
required entities in service.xml
- Define
mapping-table attribute for required entity columns
- Run
Service builder
- Use
Generated Data base services
Create
simple Liferay MVC portlet using Liferay IDE in Eclipse
Firs we need to create simple Liferay MVC portlet
using Liferay IDE in eclipse. This is very simple to create in eclipse.
The following is tutorial from setting liferay
environment.
Once you set up the development environment then you
can create portlet.
Create
service.xml file in Portlet WEB-INF directory
Now we need to create service.xml file in portlet WEB-INF directory. This is the
configuration file to service builder tool from this it will generate required
service to portlet and these service provide database interaction from portlet.
The following screen shows service.xml
file in portlet WEB-INF directory
Define required entities in service.xml
Now we need to defined required entities in
service.xml file so that service builder will generate services.
service.xml
has defined tags from which we will define entities these tags information available
in service builder DTD file.
The following is service builder DTD we can get more
information about service builder tags for service.xml
Assume we have two entities Student and Course
The
following is service.xml entities configuration
<?xml version="1.0"
encoding="UTF-8"?>
<!DOCTYPE service-builder
PUBLIC "-//Liferay//DTD
Service Builder 6.1.0//EN" "http://www.liferay.com/dtd/liferay-service-builder_6_1_0.dtd">
<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>
|
Define
mapping-table attribute for required entity
columns
We need to identify the tables which required Many to Many Relation and then we need
to define virtual column for each entity and the column should have
mapping-table and entity attributes
The following is example for Student and Course Many to Many Relation
<?xml version="1.0"
encoding="UTF-8"?>
<!DOCTYPE service-builder
PUBLIC "-//Liferay//DTD
Service Builder 6.1.0//EN" "http://www.liferay.com/dtd/liferay-service-builder_6_1_0.dtd">
<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>
|
Note:
We defined
two entities in service.xml but service builder will created 3 tables and the
third one is mapping tables which map the student and course primary keys.
Run
Service builder
Once we complete the configuration now we need run
service builder. We can run service builder in eclipse from ant view. We need
click on build-service target
from ANT view
In normal ant command for run service builder as
follows
The
following is ANT build-service in eclipse ant view
Once we run service builder then service builder
generates all java classes and configuration files along with SQL scripts.
Service builder generate Model/POJO, Service and
Util classes. Mostly we will use Util classes to use service to interact with
data bases
The following screen shows Generated classes
for Portlet
Use
Generated Data base services
Once we generated service builder services then we
can use in development
We already know we have used Student and Course
entities in service.xml so that we will get many service related to these to tables.
We will use Util classes to interact with database.
Add
Student
Student student=
StudentLocalServiceUtil.createStudent(CounterLocalServiceUtil.increment());
student.setStudentName(studentName);
student.setStudentPlace(studentPlace);
student.setStudentCollege(studentCollege);
student=StudentLocalServiceUtil.addStudent(student);
|
Add
Course
Course
course=CourseLocalServiceUtil.createCourse(CounterLocalServiceUtil.increment());
course.setCourseName(courseName);
course.setCourseGroup(courseGroup);
course=CourseLocalServiceUtil.addCourse(course);
|
Map
Multiple course to one student (this is relation mapping)
Long studentId=2000;
long[] courseIds=[100,101,102]
CourseLocalServiceUtil.addStudentCourses(studentId,
courseIds);
|
Map
Multiple Students to one Course (this is relation mapping)
Long coursetId=2000;
long[] studensIds=[100,101,102]
StudentLocalServiceUtil.addCourseStudents(courseId,
studentsIds);
|
Get
Student Courses & Get Course students
Get
Student Courses
List<Course>
studentCourseList= CourseLocalServiceUtil.getStudentCourses(studentId);
for(Student curCourse:studentCourseList){
System.out.println(curCourse.getCourseName());
}
|
Get
Course students
List<Student>
courseStudentList=StudentLocalServiceUtil.getCourseStudents(courseId);
for(Student
curStudent:courseStudentList){
System.out.println(curStudent.getStudentName());
}
|
Note:
When we use above methods I got class cast exception
so i did work around to display student courses and vice versa.
The following is I posted challenge in Liferay forum
The following is work around get each students
courses and each course students
Get
Student Courses
List
studentCoursesList=CourseLocalServiceUtil.getStudentCourses(studentId);
for(int
i=0;i<studentCoursesList.size();i++){
Object curCourse=studentCoursesList.get(i);
JSONObject
jobj=JSONFactoryUtil.createJSONObject(curCourse.toString());
System.out.println(jobj.getString("courseName"));
}
|
Get
Course Students
List courseStudentList
=StudentLocalServiceUtil.getCourseStudents(courseId);
for(int
i=0;i<studentCoursesList.size();i++){
Object curStudent=
courseStudentList.get(i);
JSONObject
jobj=JSONFactoryUtil.createJSONObject(curStudent.toString());
System.out.println(jobj.getString("studentName"));
}
|
Important
Points
- Liferay have service builder tool from which we can
generate service layer for portlet. Service layer is nothing but set of classes
and interfaces.
- Service builder use spring and hibernate to generate
service layer for portlet.
- Service
builder need one configuration file called service.xml file
in this we will defined required entities for portlet.
- Liferay service builder support many to many relation.
Mapping-table is an attribute for column from which we can achieve many to may
relation between tables.
- Generally service builder generate required SQL
scripts for portlet from the entities which are defined in service.xml
- When we use mapping-key for columns those columns
physically not exited in the table but these columns just virtual column to
make Many to Many Relation.
- Service
Builder is create all mapping tables which we used values
for mapping-key attribute.
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