Using @ManyToOne and @OneToMany causes org.hibernate.exception.GenericJDBCException

Question

I'm learning Hibernate with annotations and I got a weird exception while trying to use @OneToMany and @ManyToOne , the code is below :

Employee.java

@Entity
@Table(name = "EMPLOYEE")
public class Employee {

    @Id
    @GeneratedValue
    @Column(name="employee_id")
    private Long employeeId;

    @Column(name="firstname")
    private String firstname;

    @Column(name="lastname")
    private String lastname;

    @Column(name="birth_date")
    private Date birthDate;

    @Column(name="cell_phone")
    private String cellphone;

    @ManyToOne
    @JoinColumn(name="department_id", insertable=false, updatable=false , nullable=false)
    private Department department;

    public Employee() {

    }

    public Employee(String firstname, String lastname, String phone) {
        this.firstname = firstname;
        this.lastname = lastname;
        this.birthDate = new Date(System.currentTimeMillis());
        this.cellphone = phone;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    public Long getEmployeeId() {
        return employeeId;
    }

    public void setEmployeeId(Long employeeId) {
        this.employeeId = employeeId;
    }

    public String getFirstname() {
        return firstname;
    }

    public String getLastname() {
        return lastname;
    }

    public Date getBirthDate() {
        return birthDate;
    }

    public String getCellphone() {
        return cellphone;
    }

    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }

    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }

    public void setCellphone(String cellphone) {
        this.cellphone = cellphone;
    }

}

Department.java

@Entity
@Table(name = "DEPARTMENT")
public class Department {

    @Id
    @Column(name="DEPARTMENT_ID")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long departmentId;

    @Column(name="DEPT_NAME")
    private String departmentName;

    @OneToMany(cascade={CascadeType.ALL})
    @JoinColumn(name="department_id")
    @IndexColumn(name="idx")
    private List<Employee> employees;

    public Long getDepartmentId() {
        return departmentId;
    }

    public void setDepartmentId(Long departmentId) {
        this.departmentId = departmentId;
    }

    public String getDepartmentName() {
        return departmentName;
    }

    public void setDepartmentName(String departmentName) {
        this.departmentName = departmentName;
    }

    public List<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }
}

hibernate.cfg.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.password">root</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost/DepartmentEmployee</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="connection.pool_size">1</property>
        <property name="show_sql">true</property>
        <property name="hbm2ddl.auto">create</property>
    <mapping class="com.Department"></mapping>
    <mapping class="com.Employee"></mapping>
    </session-factory>
</hibernate-configuration>

When I try to put some records , I get this :

Exception in thread "main" org.hibernate.exception.GenericJDBCException: Field 'department_id' doesn't have a default value
    at org.hibernate.exception.internal.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:148)
    at org.hibernate.exception.internal.SQLStateConverter.convert(SQLStateConverter.java:136)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110)
    at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:129)
    at org.hibernate.engine.jdbc.internal.proxy.AbstractProxyHandler.invoke(AbstractProxyHandler.java:81)
    at com.sun.proxy.$Proxy12.executeUpdate(Unknown Source)
    at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:96)
    at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:55)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2757)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3268)
    at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:78)
    at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:273)

Something is wrong with the department_id , but I don't see the problem with it .

Any idea what causes this ?

Much appreciated

Answer 1

The exception tell you that department_id has not a default value. So change nullable value to true into Employee department field if you want nullable values.

@ManyToOne
@JoinColumn(name="department_id", insertable=false, updatable=false , nullable=true)
private Department department;

Moreover..

Department table doesn't have a column with a foreign key to the Employee table. @JoinColumn indicates that this entity is the owner of the relationship, so remove that annotation from employees field in Department class.

Then change your @OneToMany on employees adding mappedBy attribute

@OneToMany(mappedBy="department", cascade={CascadeType.ALL})
private List<Employee> employees;