mybatis 延迟加载

短命女 2024-02-19 17:47 66阅读 0赞

**第一步：在mybatis-config.xml中配置延迟加载。**

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
            PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
            "http://mybatis.org/dtd/mybatis-3-config.dtd">
    
    <configuration>
            
        <settings>
            
            <setting name="lazyLoadingEnabled" value="true"/>
            
            <setting name="aggressiveLazyLoading" value="false"/>
        </settings>
        
        <typeAliases>
            <package name="com.maven.pojo"/>
        </typeAliases>
    </configuration>

**第二步：在maven的pom文件中配置CGLIB**

<dependency>
        <groupId>cglib</groupId>
        <artifactId>cglib</artifactId>
        <version>3.2.5</version>
    </dependency>

否则会报错：（错误可能有点长抱歉，为了让大家看的更详细一写）

java.lang.IllegalStateException: Failed to load ApplicationContext

at org.springframework.test.context.CacheAwareContextLoaderDelegate.loadContext(CacheAwareContextLoaderDelegate.java:99)  
at org.springframework.test.context.DefaultTestContext.getApplicationContext(DefaultTestContext.java:101)  
at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:109)  
at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:75)  
at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:331)  
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:213)  
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:290)  
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)  
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:292)  
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:233)  
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:87)  
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)  
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)  
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)  
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)  
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)  
at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)  
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)  
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)  
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:176)  
at org.junit.runner.JUnitCore.run(JUnitCore.java:160)  
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)  
at com.intellij.rt.execution.junit.IdeaTestRunner$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)  
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sqlSessionFactory' defined in class path resource \[applicationContext.xml\]: Invocation of init method failed; nested exception is org.springframework.core.NestedIOException: Failed to parse config resource: class path resource \[mybatis-config.xml\]; nested exception is org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.lang.IllegalStateException: Cannot enable lazy loading because CGLIB is not available. Add CGLIB to your classpath.  
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1553)  
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)  
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)  
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:304)  
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)  
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:300)  
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)  
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:684)  
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:760)  
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)  
at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:125)  
at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:60)  
at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.delegateLoading(AbstractDelegatingSmartContextLoader.java:100)  
at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.loadContext(AbstractDelegatingSmartContextLoader.java:250)  
at org.springframework.test.context.CacheAwareContextLoaderDelegate.loadContextInternal(CacheAwareContextLoaderDelegate.java:64)  
at org.springframework.test.context.CacheAwareContextLoaderDelegate.loadContext(CacheAwareContextLoaderDelegate.java:91)  
... 24 more  
Caused by: org.springframework.core.NestedIOException: Failed to parse config resource: class path resource \[mybatis-config.xml\]; nested exception is org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.lang.IllegalStateException: Cannot enable lazy loading because CGLIB is not available. Add CGLIB to your classpath.  
at org.mybatis.spring.SqlSessionFactoryBean.buildSqlSessionFactory(SqlSessionFactoryBean.java:430)  
at org.mybatis.spring.SqlSessionFactoryBean.afterPropertiesSet(SqlSessionFactoryBean.java:336)  
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1612)  
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1549)  
... 39 more  
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.lang.IllegalStateException: Cannot enable lazy loading because CGLIB is not available. Add CGLIB to your classpath.  
at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:106)  
at org.apache.ibatis.builder.xml.XMLConfigBuilder.parse(XMLConfigBuilder.java:89)  
at org.mybatis.spring.SqlSessionFactoryBean.buildSqlSessionFactory(SqlSessionFactoryBean.java:424)  
... 42 more  
Caused by: java.lang.IllegalStateException: Cannot enable lazy loading because CGLIB is not available. Add CGLIB to your classpath.  
at org.apache.ibatis.executor.loader.CglibProxyFactory.<init>(CglibProxyFactory.java:50)  
at org.apache.ibatis.session.Configuration.setLazyLoadingEnabled(Configuration.java:277)  
at org.apache.ibatis.builder.xml.XMLConfigBuilder.settingsElement(XMLConfigBuilder.java:199)  
at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:100)  
... 44 more  
Caused by: java.lang.ClassNotFoundException: Cannot find class: net.sf.cglib.proxy.Enhancer  
at org.apache.ibatis.io.ClassLoaderWrapper.classForName(ClassLoaderWrapper.java:188)  
at org.apache.ibatis.io.ClassLoaderWrapper.classForName(ClassLoaderWrapper.java:87)  
at org.apache.ibatis.io.Resources.classForName(Resources.java:254)  
at org.apache.ibatis.executor.loader.CglibProxyFactory.<init>(CglibProxyFactory.java:48)  
... 47 more

**第三步：mapper.xml映射文件**

**我用的是一对多查询延迟加载 一对一查询的延迟加载和一对多的差不多一样**

延迟加载只支持**resultMap这个标签**

**主要通过：**<collection property="rows" **select="findRow" column="id"**>

**select 和column这两个标签属性**

**select ：是要查询多的一方是SQL语句，column:是两张表关联的外键属性**

（下面标记颜色的是我个人理解的他们之间的关系）

## **最主要的一句：当调用getRows()方法时后面id="findRow"那个Sql语句才执行** ##

<resultMap id="findUrow" type="com.maven.pojo.User">
        <id property="Uid" column="id"/>
        <result property="name" column="name"/>
        <result property="password" column="password"/>
        <collection property="rows" select="findRow" column="id">
        </collection>
    </resultMap>
    
    <select id="findYC" resultType="java.lang.String" resultMap="findUrow">
        SELECT * FROM USER where name=#{name};
    </select>
    <select id="findRow" resultType="int" parameterType="com.maven.pojo.Rows">
        select * from rows where u_id=#{id};
    </select>

为了更清楚一些我把自己写的pojo类粘贴上 最主要的是大家还是动手试一下才更清除。

public class User {
    
        private Integer Uid;
        private String name;
        private String password;
    
        private List<Rows> rows;
    
    }

public class Rows {
    
        private String id;
    
        private String jueSe;

｝

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