spring - jpa中使用多对多manyToManay，关于懒加载的出错问题

问题描述

问 题

先看看Company实体类：主要代码

@Table(name = "ppp_corp")
@Entity
public class Company {

    private Integer corpId;
    private String corpName;
    private Set<Department> depts = new HashSet<Department>();


    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Id
    public Integer getCorpId() {
        return corpId;
    }


    @JoinTable(name = "company_department", joinColumns = {@JoinColumn(name = "Corp_ID", referencedColumnName = "corpId")}, inverseJoinColumns = {@JoinColumn(name = "Department_ID", referencedColumnName = "deptId")})
    @ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
    public Set<Department> getDepts() {
        return depts;
    }

然后是Department实体类

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

    private Integer deptId;
    private String departName;
    private Set<Company> corps = new HashSet<Company>();


    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Id
    public Integer getDeptId() {
        return deptId;
    }

    @ManyToMany(mappedBy = "depts")
    public Set<Company> getCorps() {
        return corps;
    }

生成后运行，就出现500错误，

com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.domain.Company.depts, could not initialize proxy - no Session

后来，在@ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)改为

@ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.eager)

就会出现内存溢出。提示-1

另外，在web.xml加上过滤器：也会出现内存溢出，提示-1

<filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter<filter-class>  

因为spring用的是jap，所以用OpenEntityManagerInViewFilter。

我也试过用hibernate的rg.springframework.orm.hibernate5.support.OpenSessionInViewFilter

但是，也出错，没有noclass什么的....

貌似网上的答案都不管用了！！

有解决方法吗？

解决方案

首先，加过滤器解决懒加载问题；
内存溢出是因为陷入了死循环，一个department引出多个company属性，company又加载department集合，department又加载集合……

在集合属性前加个@JsonIgnore

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