2023-01-12

一、Mybatis动态SQL

即将SQL动态化

同时Mybatis的动态SQL支持OFNL表达式，OGNL（Object Graph Navigation Language）对象图导航语言。

1、先搭建环境

（1）创建一个“maven”模块，命名为“day04_mybatis”

（2）在“day04_mybatis”中的“pom.xml”中的<project>标签内部添加依赖，即添加jar包

<dependencies>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.26</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>

        <!-- https://mvnrepository.com/artifact/log4j/log4j -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>


    </dependencies>

（3）在"day04_mybatis.src.main.resources"中添加"db.properties（连接数据库，里面的形式是：key=value）,需要设置4个值（driver、url、username、password）"和“log4j.xml”

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
        <param name="Encoding" value="UTF-8" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n" />
        </layout>
    </appender>

    <logger name="java.sql">
        <level value="debug"/>
    </logger>

    <logger name="org.apache.ibatis">
        <level value="info"/>
    </logger>

    <root>
        <level value="debug" />
        <appender-ref ref="STDOUT" />
    </root>

</log4j:configuration>

（4）在“day04_mybatis.src.resources”中添加“mybatis-config.xml”

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!--    设置属性-->
    <properties resource="db.properties"></properties>

    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true"/>
        <!--        延迟加载-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <!--        延迟加载的属性-->
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>

    <typeAliases>
        <package name="com.hh.mybatis.poj