failed to lazily initialize a collection of role 異常

　　最近在通過配置實體類的方式，正向自動掃描注解方式配置的hibernate類文件來生成數據庫的方法搭建環境，遇到了許多問題。

　　通過數據庫配置hibernate的時候，大家都知道是在實體類對應生成的.hbm.xml文件中查看一對多和多對多的關系。

　　當報failed to lazily initialize a collection of role異常的時候，往往是因為懶加載的問題導致的。

　　可以在.hbm.xml文件中，將lazy="false"，這樣就不會報這個異常了。

　　但是在自動掃描注解方式配置的hibernate類文件時，如何將懶加載改為false呢？

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

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

 

　　舉個栗子：

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;
    }
    
    
}

這個實體類里，對應有四個一對多的外鍵關系，每一個一對多的關系查詢的時候都涉及到一個懶加載，所以說，每一個OneToMany上都要添加fetch=FetchType.EAGER