📄 index.xtp
字号:
<document> <header> <product>resin-ee</product> <title>Many-to-Many CMP</title> <description> <p>Illustrates using many-to-many relations of EJB 3.0.</p> </description> <type>tutorial</type> <tutorial-startpage>many2many</tutorial-startpage> </header> <body> <summary/><s1 title="Files in this tutorial"><deftable><tr><td><viewfile-link file="WEB-INF/resin-web.xml"/> </td><td>resin-web.xml configuration</td></tr><tr><td><viewfile-link file="WEB-INF/classes/META-INF/persistence.xml"/> </td><td>persistence.xml configuration</td></tr><tr><td><viewfile-link file="WEB-INF/classes/example/Student.java"/> </td><td>The student bean</td></tr><tr><td><viewfile-link file="WEB-INF/classes/example/Course.java"/> </td><td>The course bean</td></tr><tr><td><viewfile-link file="WEB-INF/classes/example/Grade.java"/> </td><td>The grade bean</td></tr><tr><td><viewfile-link file="WEB-INF/classes/example/ManyToManyServlet.java"/> </td><td>The course servlet</td></tr></deftable></s1><s1 title="Entity Beans"><p>The many-to-many relation connects two tables with an association table.In the example, each Student takes several Courses. A grade_map tableconnects the two. Using the many-to-many relation, the applicationcan return the student's courses or the students in a course.</p><example title="SQL Schema">CREATE TABLE Course ( course_id BIGINT PRIMARY KEY, name VARCHAR(255))CREATE TABLE Student ( student_id BIGINT PRIMARY KEY, name VARCHAR(255))CREATE TABLE grade_map ( id BIGINT PRIMARY KEY auto_increment, student_id BIGINT REFERENCES Student(student_id), course_id BIGINT REFERENCES Course(course_id))</example><p>The Course has an @Id and a data column for the name.</p><example title="Course.java"><a href="doc|amber-table.xtp#@Entity">@Entity</a>public class Course { <a href="doc|amber-table.xtp#@Id">@Id</a> <a href="doc|amber-table.xtp#@Column">@Column</a>(name="course_id") public long getId() <a href="doc|amber-table.xtp#@Basic">@Basic</a> public String getName()}</example><p>The Student includes the many-to-many relation in its definition.</p><example title="Student.java"><a href="doc|amber-table.xtp#@Entity">@Entity</a>public class Student { <a href="doc|amber-table.xtp#@Id">@Id</a> <a href="doc|amber-table.xtp#@Column">@Column</a>(name="student_id") public long getId() <a href="doc|amber-table.xtp#@Basic">@Basic</a> public String getName() <a href="doc|amber-table.xtp#@ManyToMany">@ManyToMany(targetEntity="Course")</a> <a href="doc|amber-table.xtp#@JoinTable">@JoinTable</a>( table=<a href="doc|amber-table.xtp#@Table">@Table</a>(name="student_course_map"), joinColumns=<a href="doc|amber-table.xtp#@JoinColumn">@JoinColumn</a>(name="student_id")", inverseJoinColumns=<a href="doc|amber-table.xtp#@JoinColumn">@JoinColumn</a>(name="course_id")") public Collection getCourses()}</example></s1><s1 title="@ManyToMany"><p>The <a href="doc|amber-table.xtp#@ManyToMany">@ManyToMany</a>annotation marks a collection-valued field as a many-to-many relation.The <code>targetEntity</code> value specifies the target of therelation.</p><p>Since the many-to-many relation is a three-table relation, it needsto specify the association table as well as the columns.</p></s1><s1 title="Client"><example title="ManyToManyServlet.java"> private void doService(PrintWriter out) throws java.io.IOException { PrintWriter out = res.getWriter(); res.setContentType("text/html"); Query allStudent = _entityManager.createQuery("SELECT o FROM Student o"); List students = allStudent.listResults(); for (int i = 0; i < students.size(); i++) { Student student = (Student) students.get(i); out.println("<h3>" + student.getName() + "</h3>"); Collection courses = student.getCourses(); out.println("<ul>"); Iterator iter = courses.iterator(); while (iter.hasNext()) { Course course = (Course) iter.next(); out.println("<li>" + course.getName()); } out.println("</ul>"); } }}</example></s1> </body></document>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -