解决Spring Data JPA延迟加载no session错误

项目采用spring boot构建，提供restful接口给PHP调用，接口类统一使用@RestController注解

实体关系

	@ManyToOne(fetch = FetchType.LAZY)

	@JoinColumn(name = "department_id")
	private Department department;

	@OneToMany(mappedBy = "department", fetch = FetchType.LAZY)
	private Set employees;

单元测试

	@Test
	public void testGet() {
		Department dept = deptService.get(1L);
		Assert.assertEquals("IT", dept.getName());
		Set employees = dept.getEmployees();
		Assert.assertEquals(2, employees.size());
	}

异常信息

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.ai.demo.entity.Department.employees, could not initialize proxy - no Session
	at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:587)
	at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:204)
	at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:148)
	at org.hibernate.collection.internal.PersistentSet.size(PersistentSet.java:143)
	at com.ai.demo.service.DepartmentServiceTests.testGet(DepartmentServiceTests.java:37)
	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.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:252)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
	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:191)
	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

解决LazyInitializationException异常大概有这么几种方式
1.关闭LazyInitialization, 将fetch设成eager

2.在spring boot的配置文件application.properties添加spring.jpa.open-in-view=true

3.用spring 的OpenSessionInViewFilter

第一种方式显然不好，无法使用到延迟加载的特性，会带来性能问题

后面两种方式只能用在Servlet容器下,而当我们在spring boot环境下运行单元测试的时候是无法启用OpenSessionInViewFilter的

其实要解决这种情况下的问题也很简单，只需要在单元测试方法@Transactional注解即可解决

	@Test
	@Transactional
	public void testGet() {
		Department dept = deptService.get(1L);
		Assert.assertEquals("IT", dept.getName());
		Set employees = dept.getEmployees();
		Assert.assertEquals(2, employees.size());
	}