ids for this class must be manually assigned before calling save()

org.springframework.orm.hibernate4.HibernateSystemException: ids for this class must be manually assigned before calling save(): com.mjlf.spring_data_access.entity.School; nested exception is org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.mjlf.spring_data_access.entity.School

    at org.springframework.orm.hibernate4.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:218)
    at org.springframework.orm.hibernate4.HibernateTemplate.doExecute(HibernateTemplate.java:344)
    at org.springframework.orm.hibernate4.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:309)
    at org.springframework.orm.hibernate4.HibernateTemplate.save(HibernateTemplate.java:618)
    at com.mjlf.spring_data_access.hibernate.HibernateSchoolDao.addSchool(HibernateSchoolDao.java:20)
    at com.mjlf.spring_data_access.HibernateDataAccessTest.testSave(HibernateDataAccessTest.java:24)
    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.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:84)
    at org.testng.internal.MethodInvocationHelper$1.runTestMethod(MethodInvocationHelper.java:200)
    at org.springframework.test.context.testng.AbstractTestNGSpringContextTests.run(AbstractTestNGSpringContextTests.java:175)
    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.testng.internal.MethodInvocationHelper.invokeHookable(MethodInvocationHelper.java:212)
    at org.testng.internal.Invoker.invokeMethod(Invoker.java:707)
    at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:901)
    at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1231)
    at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:127)
    at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:111)
    at org.testng.TestRunner.privateRun(TestRunner.java:767)
    at org.testng.TestRunner.run(TestRunner.java:617)
    at org.testng.SuiteRunner.runTest(SuiteRunner.java:334)
    at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:329)
    at org.testng.SuiteRunner.privateRun(SuiteRunner.java:291)
    at org.testng.SuiteRunner.run(SuiteRunner.java:240)
    at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
    at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
    at org.testng.TestNG.runSuitesSequentially(TestNG.java:1224)
    at org.testng.TestNG.runSuitesLocally(TestNG.java:1149)
    at org.testng.TestNG.run(TestNG.java:1057)
    at org.testng.IDEARemoteTestNG.run(IDEARemoteTestNG.java:72)
    at org.testng.RemoteTestNGStarter.main(RemoteTestNGStarter.java:123)
Caused by: org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.mjlf.spring_data_access.entity.School
    at org.hibernate.id.Assigned.generate(Assigned.java:52)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:117)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:204)
    at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:55)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:189)
    at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:49)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:90)
    at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:763)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:755)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:751)
    at org.springframework.orm.hibernate4.HibernateTemplate$12.doInHibernate(HibernateTemplate.java:622)
    at org.springframework.orm.hibernate4.HibernateTemplate$12.doInHibernate(HibernateTemplate.java:618)
    at org.springframework.orm.hibernate4.HibernateTemplate.doExecute(HibernateTemplate.java:341)
    ... 34 more

解决办法：
xml配置：主键处添加

<hibernate-mapping auto-import="true" default-lazy="false">
    <class name="com.mjlf.spring_data_access.entity.School" table="school_tbl">
        <id name="id" column="id" type="java.lang.Integer">
            <generator class="native" />
        id>
        <property name="name" column="name" type="java.lang.String" />
    class>
hibernate-mapping>

注解类型：主键添加
@GeneratedValue(strategy = GenerationType.IDENTITY)

@Entity
@Table(name = "school_tbl")
public class School implements Serializable {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "name")
    private String name;

    public School() {
    }

    public School(String name) {
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "School{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}