Mybatis之延遲加載機制

時間  2020-05-15
標籤 mybatis 延遲 加載 機制 欄目 MyBatis 简体版
原文   原文鏈接

1.  延遲加載的含義： 用到的時候纔會去進行相關操做java

2.  延遲加載的例子：mysql

    2.1 spring的BeanFactory，在getBean（）的時候才建立Beanspring

    2.2 物理分頁查詢，只有點擊某一頁時採起數據庫查詢該頁的數據sql

3. Mybatis啓用延遲加載機制數據庫

<setting name="lazyLoadingEnabled" value="true"/>

4. Mybatis延遲加載的策略：apache

　　侵入式延遲加載機制【若是隻查詢主表數據而不進行使用，級聯表的數據不會被查詢；若是使用了主表數據，即便級聯表的數據沒有使用，也會查詢】服務器

    4.1 實例一：只查詢主表數據而不進行使用session

package com.blueStarWei.test;

import java.util.List;

import org.apache.ibatis.session.SqlSession;

import com.blueStarWei.entity.TPersonInfo;
import com.blueStarWei.mappers.PersonAddressMapper;
import com.blueStarWei.utils.SqlSessionFactoryUtil;

public class TestPersonAddress {

    public static void main(String[] args) {
        SqlSession session = SqlSessionFactoryUtil.openSession();
        PersonAddressMapper mapper = session.getMapper(PersonAddressMapper.class);
        
        List<TPersonInfo> info = mapper.findAllWithAddress();
        
    }
}

        4.1.1 日誌mybatis

[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Opening JDBC Connection
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Created connection 836514715.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@31dc339b]
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-==>  Preparing: select * from t_person_info 
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-==> Parameters: 
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-<==      Total: 1

    4.2 實例二：查詢並使用主表數據app

package com.blueStarWei.test;

import java.util.List;

import org.apache.ibatis.session.SqlSession;

import com.blueStarWei.entity.TPersonInfo;
import com.blueStarWei.mappers.PersonAddressMapper;
import com.blueStarWei.utils.SqlSessionFactoryUtil;

public class TestPersonAddress {

    public static void main(String[] args) {
        SqlSession session = SqlSessionFactoryUtil.openSession();
        PersonAddressMapper mapper = session.getMapper(PersonAddressMapper.class);
        
        List<TPersonInfo> info = mapper.findAllWithAddress();
        
        for (TPersonInfo tPersonInfo : info) {
            System.out.println(tPersonInfo.getName());
        }
    }
}

        4.2.2 日誌

[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Opening JDBC Connection
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Created connection 836514715.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@31dc339b]
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-==>  Preparing: select * from t_person_info [com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-==> Parameters: 
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-<==      Total: 1
[com.blueStarWei.mappers.AddressMapper.findById]-==>  Preparing: SELECT * FROM t_address t where t.id = ? 
[com.blueStarWei.mappers.AddressMapper.findById]-==> Parameters: 1(Integer)
[com.blueStarWei.mappers.AddressMapper.findById]-<==      Total: 1

5. Mybatis禁用侵入式延遲加載【使用到數據纔會去查找相關表】

<setting name="aggressiveLazyLoading" value="false"/>

    5.1 實例一：只使用主表數據

package com.blueStarWei.test;

import java.util.List;

import org.apache.ibatis.session.SqlSession;

import com.blueStarWei.entity.TPersonInfo;
import com.blueStarWei.mappers.PersonAddressMapper;
import com.blueStarWei.utils.SqlSessionFactoryUtil;

public class TestPersonAddress {

    public static void main(String[] args) {
        SqlSession session = SqlSessionFactoryUtil.openSession();
        PersonAddressMapper mapper = session.getMapper(PersonAddressMapper.class);
        
        List<TPersonInfo> info = mapper.findAllWithAddress();
        
        for (TPersonInfo tPersonInfo : info) {
            System.out.println(tPersonInfo.getName());
        }
    }
}

        5.1.1 日誌

[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Opening JDBC Connection
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Created connection 836514715.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@31dc339b]
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-==>  Preparing: select * from t_person_info [com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-==> Parameters: 
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-<==      Total: 1

    5.2 實例二：使用級聯表數據

package com.blueStarWei.test;

import java.util.List;

import org.apache.ibatis.session.SqlSession;

import com.blueStarWei.entity.TPersonInfo;
import com.blueStarWei.mappers.PersonAddressMapper;
import com.blueStarWei.utils.SqlSessionFactoryUtil;

public class TestPersonAddress {

    public static void main(String[] args) {
        SqlSession session = SqlSessionFactoryUtil.openSession();
        PersonAddressMapper mapper = session.getMapper(PersonAddressMapper.class);
        
        List<TPersonInfo> info = mapper.findAllWithAddress();
        
        for (TPersonInfo tPersonInfo : info) {
            System.out.println(tPersonInfo.getAddress());
        }
    }
}

         5.2.1 日誌

[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Opening JDBC Connection
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Created connection 836514715.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@31dc339b]
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-==>  Preparing: select * from t_person_info 
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-==> Parameters: 
[com.blueStarWei.mappers.PersonAddressMapper.findAllWithAddress]-<==      Total: 1
[com.blueStarWei.mappers.AddressMapper.findById]-==>  Preparing: SELECT * FROM t_address t where t.id = ? 
[com.blueStarWei.mappers.AddressMapper.findById]-==> Parameters: 1(Integer)
[com.blueStarWei.mappers.AddressMapper.findById]-<==      Total: 1

6. 補充

    6.1 啓用log4j打印日誌

        導入log4j.jar， 將log4j.properties文件與ybatis-config.xml放到一塊兒【會自動加載，無需配置】

7.附錄：

    7.1 建表語句【Mysql】

CREATE TABLE `t_person_info` (
   `id` int(2) NOT NULL AUTO_INCREMENT,
   `name` varchar(10) DEFAULT NULL,
   `age` int(3) DEFAULT NULL,
   `addressId` int(3) DEFAULT NULL,
   PRIMARY KEY (`id`)
 ) 

CREATE TABLE `t_address` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `country` varchar(10) DEFAULT NULL,
   `city` varchar(10) DEFAULT NULL,
   PRIMARY KEY (`id`)
 )

    7.2 mybatis-config.xml

<?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>
    <properties resource="jdbc.properties"/>
    
    <settings>
        <!-- 延遲加載的全局開關。當開啓時，全部的關聯對象會延遲加載 。默認false-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <!-- 禁用侵入式延遲加載 -->
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>
    
    <!-- 類型別名：給Java類起一個簡單的名字 -->
    <typeAliases>
        <package name="com.blueStarWei.entity"/>
    </typeAliases>
    
    
    <!-- 環境信息 -->
    <environments default="development">
        <environment id="development">
            <!-- myBatis支持兩種事務管理：JDBC和MANAGED(託管) 
                 MANAGED通常商業服務器纔有此功能，例如JBOSS-->
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driverClassName}" />
                <property name="url" value="${jdbc.url}" />
                <property name="username" value="${jdbc.username}" />
                <property name="password" value="${jdbc.password}" />
            </dataSource>
        </environment>
    </environments>
    
    <mappers>
        <package name="com.blueStarWei.mappers"/>
    </mappers>
</configuration>

    7.3 TpersonInfo.java

package com.blueStarWei.entity;

public class TPersonInfo {
    
    private Integer id;
    private String name;
    private Integer age;
    private Address address;
    
    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;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    
    public Address getAddress() {
        return address;
    }
    public void setAddress(Address address) {
        this.address = address;
    }
    
}

    7.4 Addreess.java

package com.blueStarWei.entity;

public class Address {
    
    private int id;
    private String country;
    private String city;
    
    public String getCountry() {
        return country;
    }
    public void setCountry(String country) {
        this.country = country;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    @Override
    public String toString() {
        return "Address [country=" + country + ", city=" + city + "]";
    }
    
}

    7.5 log4j.properties

log4j.rootLogger=debug,console
 
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=[%c]-%m%n

    7.6 mybatis相關架包：

        https://pan.baidu.com/s/1248sNRHReiK8S3pENKfmlA  密碼：xpe7

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