how to auto. create association tables

oftsky · **Joined:** Fri May 25, 2007 4:42 am **Posts:** 13

hi, just try hibernate annotation,
have two classes, Project *-* employees
want to auto create a new association-table to DB, can hibernate annotation do that? or i must manuelly create a such kind of table to DB?

like toturial:
@Entity
public class Store {
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
public Set<Customer> getCustomers() {
...
}
}

@Entity
public class Customer {
@ManyToMany(mappedBy="customers")
public Set<Store> getStores() {
...
}
}

these two classes can created both tables store and customer, and can auto create a asso. table Store_Customer?

have tryed my classes, can not do that, why?
@Entity
@Table(catalog="vipinfo", name="project")

public class Project implements java.io.Serializable {
......
@ManyToMany(
targetEntity=Employee.class,
cascade={CascadeType.PERSIST, CascadeType.MERGE}
)
@JoinTable(
name="PROJECT_EMPLOYEE_REL",
joinColumns={@JoinColumn(name="PROJECT")},
inverseJoinColumns={@JoinColumn(name="EMPLOYEE")}
)

private Collection<Employee> involvedEmployees = new HashSet<Employee>(0);
......}

@Entity
@Table(catalog="vipinfo", name="employee")

public class Employee implements java.io.Serializable {
......
@ManyToMany(
cascade={CascadeType.PERSIST, CascadeType.MERGE},
mappedBy="involvedEmployees",
targetEntity=Project.class)

private Collection<Project> associatedProjects = new HashSet<Project>(0);
......}

andydale · **Posted:** Fri May 25, 2007 7:08 am

Hi,

Hibernate can definitely create the association table automatically, as i have done this many times. First thing to check is you hbm2ddl task settings (should be "create" or "update").

Antoher thing worth trying would be, to alter the @JoinColumn annotations in the @JoinTable, so they look something like so

Code:

@JoinTable( 
name="PROJECT_EMPLOYEE_REL", 
joinColumns={@JoinColumn(name="PROJECT", referencedColumnName="<name of id column>")}, 
inverseJoinColumns={@JoinColumn(name="EMPLOYEE", referencedColumnName="<name of id column>)} 
)

If that does not work, you can try defining your JoinTable on the other side of the relationship (in Employee).

Thanks,

Andy

oftsky · **Joined:** Fri May 25, 2007 4:42 am **Posts:** 13

Caused by: org.hibernate.HibernateException: Missing table: PROJECT_EMPLOYEE_REL

thanx, but does not work,
can u give a example of urs?

oftsky · **Joined:** Fri May 25, 2007 4:42 am **Posts:** 13

solved , danke andydale

andydale · **Posted:** Fri May 25, 2007 7:52 am

No problem. I have a many to many between student and course like so:

In Course.java

Code:

@Entity
@Table(name = "Course")
@SequenceGenerator(name = "Course_Sequence", allocationSize=1, sequenceName = "course_seq")
public final class Course implements Serializable {
   /**
     * The list of student's enrolled on the course.
     */ 
    private Set<Student> mEnrolledStudents = new HashSet<Student>();

...........

 /**
     * Return the students enrolled on the course.
     * @return mEnrolledStudents student's
     */    
    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(name = "course_student",
                joinColumns = @JoinColumn(name = "course_id", referencedColumnName = "course_id"),
                inverseJoinColumns = @JoinColumn(name = "student_id", referencedColumnName = "student_id"))   
    public Set<Student> getStudents() {        
        return mEnrolledStudents;
    }


    /**
     * Set the students enrolled on this course.
     * @param pEnrolledStudents students
     */
    public void setStudents(final Set<Student> pEnrolledStudents) {
        this.mEnrolledStudents = pEnrolledStudents;
    }

...........
}

And in Student

Code:

@Entity
@Table(name = "Student")
@SequenceGenerator(name = "Student_Sequence", allocationSize=1, sequenceName = "student_seq")
public final class Student implements Serializable {

    /**
     * Course student is enrolled on
     */
    private Collection<Course> mCourses = new ArrayList<Course>();

.........

   /**
     * Return the courses the student is enrolled on.
     * @return mCourses courses
     */
    @ManyToMany(mappedBy = "students", cascade ={CascadeType.PERSIST, CascadeType.MERGE})
    public Collection<Course> getCourses() {
        return mCourses;
    }
    
    /**
     * See the course the student is enrolled on
     * @param pCoursesEnrolledOn courses
     */
    public void setCourses(final Collection<Course> pCourses) {
        this.mCourses = pCourses;
    }

...........
}

Let me know how you get on

Cheers,

Andy

oftsky · **Joined:** Fri May 25, 2007 4:42 am **Posts:** 13

1. create and update are both ok for create associated-table
2. referencedColumnName="<name of id column>" is optional, if not write this , use the default primary key (see "is ok")
3. my problem is, in my database i have used many catalog(schema)

for entity entity class, i have written:
@Entity
@Table(catalog="vipinfo", name="project") ///*****
public class Project implements java.io.Serializable {

but i forget it for join-table

public class Project implements java.io.Serializable {

@JoinTable(
catalog="vipinfo", //*** if not write, the talbe will be under default catalog
name="PROJECT_EMPLOYEE_REL",
joinColumns={@JoinColumn(name="PROJECT")}, //is ok
inverseJoinColumns = {@JoinColumn( name="EMPLOYEE")} //is ok
//joinColumns={@JoinColumn(name="PROJECT", referencedColumnName="PRO_ID")},
//inverseJoinColumns = {@JoinColumn( name="EMPLOYEE", referencedColumnName="EMP_ID")}
)

ur tipp encourage me to find my mistake , thanx