java - 在 @ManyToMany 映射中，未将数据插入数据库(空指针异常)

Question

我是 Jpa 和 hibernate 的新手。我尝试在 jpa 中使用 @ManytoMany 映射并将该类用作:

用户.java 包 com.jpa.manytomany.manytomany.model;

import javax.persistence.*;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
import java.util.List;

@Entity
public class User {

    @Id
    @GeneratedValue
    private Long id;


    @NotNull
    @Size(max = 100)
    @Column(unique = true)
    private String userName;

    @NotNull
    @Size(max=100)
    @Column(unique = true)
    private String password;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name="user_role",joinColumns=@JoinColumn(name="user_id"),
            inverseJoinColumns = @JoinColumn(name="role_id"))
    private List<Role> roles;


    public User() {
    }

    public User(String userName, String password) {

        this.userName = userName;
        this.password = password;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public List<Role> getRoles() {
        return roles;
    }

    public void setRoles(Role role) {
       this.roles.add(role);
    }
}

角色.java

package com.jpa.manytomany.manytomany.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.validation.constraints.NotNull;
import java.util.ArrayList;
import java.util.List;

@Entity
public class Role {

    @Id
    @GeneratedValue
    private Long id;

    @NotNull
    private String roleName;

    @ManyToMany(mappedBy = "roles")
    private List<User> users=new ArrayList<>();

    public Role() {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getRoleName() {
        return roleName;
    }

    public void setRoleName(String roleName) {
        this.roleName = roleName;
    }

    public Role(String roleName) {
        this.roleName = roleName;
    }

    public List<User> getUsers() {
        return users;
    }

    public void setUsers(User user) {
        this.users.add(user);
    }
}

我使用了 hibernate 的自动表生成器属性，它生成为:

我编写了一个测试用例，将数据插入到这三个表中，如下所示:

package com.jpa.manytomany.manytomany;

import com.jpa.manytomany.manytomany.model.Role;
import com.jpa.manytomany.manytomany.model.User;
import com.jpa.manytomany.manytomany.repository.RoleRepository;
import com.jpa.manytomany.manytomany.repository.UserRepository;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class ManytomanyApplicationTests {

    private Logger logger= LoggerFactory.getLogger(this.getClass());

    @Autowired
    private RoleRepository roleRepository;

    @Autowired
    private UserRepository userRepository;

    @Test
    public void insert_into_three_tables() {
        User user=new User("Ashwin","password1");

        Role role=new Role("ROLE_ADMIN");

        userRepository.insertUserAndRole(user,role);
    }

}

用户存储库是:

package com.jpa.manytomany.manytomany.repository;

import com.jpa.manytomany.manytomany.model.Role;
import com.jpa.manytomany.manytomany.model.User;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

import javax.persistence.EntityManager;
import javax.transaction.Transactional;

@Repository
@Transactional
public class UserRepository {

    private Logger logger= LoggerFactory.getLogger(this.getClass());

    @Autowired
    private EntityManager entityManager;



    public void insertUserAndRole(User user, Role role) {
        user.setRoles(role);
        role.setUsers(user);

        entityManager.persist(user);
        entityManager.persist(role);
    }
}

角色存储库是:

package com.jpa.manytomany.manytomany.repository;

import com.jpa.manytomany.manytomany.model.Role;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

import javax.persistence.EntityManager;
import javax.transaction.Transactional;

@Repository
@Transactional
public class RoleRepository {

    @Autowired
    private EntityManager em;


    public Role insertRole(Role role){
      em.persist(role);
      return  role;
    }
}

我收到的错误是:

java.lang.NullPointerException
    at com.jpa.manytomany.manytomany.model.User.setRoles(User.java:70)
    at com.jpa.manytomany.manytomany.repository.UserRepository.insertUserAndRole(UserRepository.java:29)
    at com.jpa.manytomany.manytomany.repository.UserRepository$$FastClassBySpringCGLIB$$63f7afd9.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:749)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:295)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)
    at com.jpa.manytomany.manytomany.repository.UserRepository$$EnhancerBySpringCGLIB$$2a8fc203.insertUserAndRole(<generated>)
    at com.jpa.manytomany.manytomany.ManytomanyApplicationTests.insert_into_three_tables(ManytomanyApplicationTests.java:33)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

Answer 1

角色需要使用列表进行初始化

private List<Role> roles= new ArrayList<Role>();