TomasEdision 2009-12-14
在一对多的问题中遇到Exception如下:
org.hibernate.exception.SQLGrammarException: could not initialize a collection
Department如下:
package com.domain; import java.util.Set; public class Department { private int id; private String deptname ; private Set<Employee> emps; public Set<Employee> getEmps() { return emps; } public void setEmps(Set<Employee> emps) { this.emps = emps; } public Department() { } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getDeptname() { return deptname; } public void setDeptname(String deptname) { this.deptname = deptname; } }
测试如下:
public class ManyToOneTest { public static void main(String[] args) { Set<Employee> emps = queryEmpByDeptID(1); for (Employee emp : emps) { System.out.println(emp.getId() + " " + emp.getName()); } System.out.println("----end----"); } static Set<Employee> queryEmpByDeptID(int deptid) { Session session = null; Transaction tx = null; Department dept = new Department(); [b]Set[/b]<Employee> emps; try { session = HibernateUtil.getSession(); dept = (Department) session.get(Department.class, deptid); Hibernate.initialize(dept.getEmps()); System.out.println(dept.getEmps().size()); emps = [b](Set)[/b] dept.getEmps(); return emps; } catch (HibernateException e) { throw e; } finally { if (session != null) { session.close(); } } } }
开始测试的时候,没有注意类型要一致,用了List类型,结果就出现了
org.hibernate.exception.SQLGrammarException: could not initialize a collection
在Department中尽量不用List作为集合的类型,原因如下:
listsareindexedcollectionsandthereforneedaindexcolumn