failed to lazily initialize a collection of role 异常

　　最近在通过配置实体类的方式，正向自动扫描注解方式配置的hibernate类文件来生成数据库的方法搭建环境，遇到了许多问题。

　　通过数据库配置hibernate的时候，大家都知道是在实体类对应生成的.hbm.xml文件中查看一对多和多对多的关系。

　　当报failed to lazily initialize a collection of role异常的时候，往往是因为懒加载的问题导致的。

　　可以在.hbm.xml文件中，将lazy="false"，这样就不会报这个异常了。

　　但是在自动扫描注解方式配置的hibernate类文件时，如何将懒加载改为false呢？

　　只需要一句话，在注解上添加fetch=FetchType.EAGER便可

@OneToMany(mappedBy="user",fetch=FetchType.EAGER)

　　举个栗子：

package com.maya.entity;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;
import org.springframework.context.annotation.Lazy;

@Entity
@Table(name="t_user")

public class User {

    private Integer id;
    private String password;
    private String ename;
    private String sex;
    //private String dept;
    //private Dept dept;
    private String tel;
    private String description;

    private List<WarehouseMain> warehouseMainList=new ArrayList<WarehouseMain>();
    private List<ReWarehouseMain> reWarehouseMainList=new ArrayList<ReWarehouseMain>();
    private List<SellMain> sellMainList=new ArrayList<SellMain>();
    private List<ReSellMain> reSellMainList=new ArrayList<ReSellMain>();

    @Id
    @GenericGenerator(name = "generator", strategy = "native")
    @GeneratedValue(generator = "generator")
    @Column(name = "id", length=11)
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    @Column(name = "password", length = 20)
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    @Column(name = "ename", length = 20)
    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }
    @Column(name = "sex", length = 10)
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    /*
    @ManyToOne
    @JoinColumn(name="dept_id")
    public Dept getDept() {
        return dept;
    }
    public void setDept(Dept dept) {
        this.dept = dept;
    }*/
    @Column(name = "tel", length = 20)
    public String getTel() {
        return tel;
    }
    public void setTel(String tel) {
        this.tel = tel;
    }
    @Column(name = "description", length = 100)
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    @OneToMany(mappedBy="user",fetch=FetchType.EAGER)
    public List<WarehouseMain> getWarehouseMainList() {
        return warehouseMainList;
    }
    public void setWarehouseMainList(List<WarehouseMain> warehouseMainList) {
        this.warehouseMainList = warehouseMainList;
    }
    @OneToMany(mappedBy="user",fetch=FetchType.EAGER)
    public List<ReWarehouseMain> getReWarehouseMainList() {
        return reWarehouseMainList;
    }
    public void setReWarehouseMainList(List<ReWarehouseMain> reWarehouseMainList) {
        this.reWarehouseMainList = reWarehouseMainList;
    }
    @OneToMany(mappedBy="user",fetch=FetchType.EAGER)
    public List<SellMain> getSellMainList() {
        return sellMainList;
    }
    public void setSellMainList(List<SellMain> sellMainList) {
        this.sellMainList = sellMainList;
    }
    @OneToMany(mappedBy="user",fetch=FetchType.EAGER)
    public List<ReSellMain> getReSellMainList() {
        return reSellMainList;
    }
    public void setReSellMainList(List<ReSellMain> reSellMainList) {
        this.reSellMainList = reSellMainList;
    }

}

这个实体类里，对应有四个一对多的外键关系，每一个一对多的关系查询的时候都涉及到一个懒加载，所以说，每一个OneToMany上都要添加fetch=FetchType.EAGER