fastapi sessionid 会话保持

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mob64ca1418736f 2024-12-30 08:38:12

引言： JPA是一种非常流行和常用的持久化框架标准，其下可以对接若干种不同的实现，在不同的父子表管理中，经常会碰到no Session的问题，该如何解决呢？

1. 问题的引出

在进行基于JPA的单元测试中，我们使用JUnit来进行测试数据库的关联表信息读取，结果得到如下错误信息：

1. org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.rain.wx.meal.model.DishCategory.dishes, could not initialize proxy - no Session  
2.     at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:587)  
3.     at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:204)  
4.     at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:566)  
5.     at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:135)  
6.     at org.hibernate.collection.internal.PersistentBag.get(PersistentBag.java:449)  
7.     at com.rain.wx.meal.service.DishServiceTest.testDishes(DishServiceTest.java:86)  
8.     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)  
9.     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)  
10.     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)  
11.     at java.lang.reflect.Method.invoke(Method.java:497)  
12.     at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)  
13.     at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)  
14.     at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)  
15.     at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)  
16.     at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)  
17.     at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)  
18.     at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)  
19.     at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)  
20.     at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:252)  
21.     at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)  
22.     at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)  
23.     at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)  
24.     at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)  
25.     at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)  
26.     at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)  
27.     at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)  
28.     at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)  
29.     at org.junit.runners.ParentRunner.run(ParentRunner.java:363)  
30.     at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)  
31.     at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)  
32.     at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)  
33.     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)  
34.     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)  
35.     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)  
36.     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

经过分析，其中的关键词是： could not initialize proxy - no Session; 基于JPA的实现来分析，就是在进行数据库访问之时，当前针对数据库的访问与操作session已经关闭且释放了，故提示no Session可用。

2. 代码实现分析

让我们来看看具体的代码吧

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1. @Entity  
2. @Table(name="dish_category")  
3. @Data  
4. @EqualsAndHashCode(callSuper=false)  
5. @JsonRootName(value="category")   
6. public class DishCategory extends BaseEntity {  
7. serialVersionUID = -7189824224534351030L;  
8.   
9.     @Column  
10.     private String name;  
11.       
12.     @Column  
13.     private String description;  
14.       
15.       
16.     @OneToMany  
17. name="category_id",referencedColumnName="id")  
18. <MealDish> dishes;  
19. }

另外一个实体Bean为MealDish, 其代码为：

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1. @Entity  
2. @Table(name = "dish")  
3. @JsonRootName(value="dish")   
4. //@Lazy(value=false)  
5. public class MealDish extends BaseEntity {  
6. serialVersionUID = -3982356728880195795L;  
7.   
8.     @Column  
9.     private String name;  
10.   
11.     @Column  
12.     private float price;  
13.   
14. name = "img_url")  
15.     private String imgUrl;  
16.   
17. name="category_id")  
18.     private long categoryId;  
19.   
20.     @Column  
21.     private boolean active;  
22.   
23.     // 销售数量  
24.     @Column  
25.     private int soldCount;  
26.         .......  
27. }

其中Repository/Service的代码分别如下：

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1. @Service  
2. public class DishServiceImpl implements DishService {   
3.        @Transactional  
4.     @Override  
5. <DishCategory> getDishCategory() {  
6.         return this.dishCategoryRepo.findAll();  
7.     }  
8.    ........  
9.  }

Repository相关的代码都是空代码，无实际的实现，这里再次忽略。

单元测试的代码内容：

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1. @Test  
2.    public void testDishes() throws JsonProcessingException {  
3. mapper = new ObjectMapper();  
4.       
5. <DishCategory> categories = this.dishService.getDishCategory();  
6.       
7.     for (DishCategory category  : categories) {  
8.         // log.debug(String.valueOf(category.getDishes().get(0)));    
9.     }  
10.       
11. jsonStr = mapper.writeValueAsString(categories);  
12.       
13.     log.info(jsonStr);  
14.    }

3. 问题分析

基于对Hibernate和JPA的理解，在ORM中，其为了提升性能使用了Lazy加载，就是在使用的时候，才会加载额外的数据，故导致了在使用之时再加载数据之时， session失效的问题出现。所以问题的目标点实现提前加载数据。

4. 问题的解决

尝试1：在Service方法中新增了@Transactional进行事务添加

结果1：无效

尝试2：在@OneToMany的方法上，使用@Lazy(false)

结果2：无效

尝试3：在@OneToMany的参数中使用fetch=FetchType=Eager

结果3: 问题解决

尝试4：在application.properties的配置文件中新增spring.jpa.open-in-view=true

结果4：问题解决

方法3的正确的代码内容：

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1. @Entity  
2. @Table(name="dish_category")  
3. @Data  
4. @EqualsAndHashCode(callSuper=false)  
5. @JsonRootName(value="category")   
6. public class DishCategory extends BaseEntity {  
7. serialVersionUID = -7189824224534351030L;  
8.   
9.     @Column  
10.     private String name;  
11.       
12.     @Column  
13.     private String description;  
14.       
15.       
16. fetch=FetchType.EAGER)  
17. name="category_id",referencedColumnName="id")  
18. <MealDish> dishes;  
19. }

方法4的解释与说明：

这个设置选项:

spring.jpa.open-in-view=true

其实是之前的 openEntityManagerInViewInterceptor ，解决在Spring MVC与JPA之间Session的声明周期问题

5. 总结

核心问题在于解决延迟加载为及时加载，及时加载会消耗一定的资源，将其程序的性能，请注意这个问题。

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