MyBatis的基礎(chǔ)知識(shí)本課程將深入淺出地介紹MyBatis框架的基礎(chǔ)知識(shí)，包括其發(fā)展歷程、核心組件、配置、數(shù)據(jù)類型、動(dòng)態(tài)SQL語(yǔ)句、參數(shù)傳遞、結(jié)果集映射、緩存機(jī)制、注解開(kāi)發(fā)以及與Spring框架的整合。MyBatis簡(jiǎn)介定義MyBatis是一個(gè)持久層框架，它提供了將Java對(duì)象映射到數(shù)據(jù)庫(kù)記錄的機(jī)制，簡(jiǎn)化了數(shù)據(jù)庫(kù)操作。優(yōu)勢(shì)MyBatis具有簡(jiǎn)單易用、靈活高效、支持多種數(shù)據(jù)庫(kù)、性能優(yōu)越等特點(diǎn)。MyBatis的發(fā)展歷程12002年iBatis誕生，是一個(gè)基于Java的開(kāi)源持久層框架。22010年iBatis更名為MyBatis，并加入了新的功能和特性。32013年MyBatis3.0發(fā)布，引入了注解開(kāi)發(fā)方式。42016年MyBatis3.4發(fā)布，增加了對(duì)SpringBoot的支持。MyBatis的特點(diǎn)1簡(jiǎn)單易用使用XML或注解配置，語(yǔ)法簡(jiǎn)潔易懂。2靈活高效支持自定義SQL語(yǔ)句，能夠滿足各種復(fù)雜的業(yè)務(wù)需求。3支持多種數(shù)據(jù)庫(kù)可以無(wú)縫地與各種主流數(shù)據(jù)庫(kù)進(jìn)行連接。4性能優(yōu)越通過(guò)緩存機(jī)制和動(dòng)態(tài)SQL語(yǔ)句提高性能。為什么使用MyBatis提高開(kāi)發(fā)效率簡(jiǎn)化了數(shù)據(jù)持久層操作，降低了開(kāi)發(fā)成本。增強(qiáng)代碼可讀性通過(guò)XML或注解配置，使代碼結(jié)構(gòu)清晰易懂。提高代碼可維護(hù)性將SQL語(yǔ)句與Java代碼分離，方便維護(hù)和修改。MyBatis的工作原理1.加載配置文件加載MyBatis配置文件（SqlMapConfig.xml）和映射文件。2.創(chuàng)建SqlSessionFactory根據(jù)配置文件創(chuàng)建SqlSessionFactory對(duì)象。3.獲取SqlSession從SqlSessionFactory獲取SqlSession對(duì)象。4.執(zhí)行SQL語(yǔ)句通過(guò)SqlSession執(zhí)行SQL語(yǔ)句，并將結(jié)果映射到Java對(duì)象。5.關(guān)閉SqlSession完成操作后，關(guān)閉SqlSession對(duì)象。MyBatis的核心組件SqlSessionFactory負(fù)責(zé)創(chuàng)建SqlSession對(duì)象。SqlSession執(zhí)行SQL語(yǔ)句，并將結(jié)果映射到Java對(duì)象。Mapper定義SQL語(yǔ)句和結(jié)果映射規(guī)則。配置數(shù)據(jù)源<environmentid="development"><transactionManagertype="JDBC"></transactionManager><dataSourcetype="POOLED"><propertyname="driver"value="com.mysql.cj.jdbc.Driver"/><propertyname="url"value="jdbc:mysql://localhost:3306/mybatis_db?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai"/><propertyname="username"value="root"/><propertyname="password"value="password"/></dataSource></environment>編寫(xiě)SqlMapConfig.xml<?xmlversion="1.0"encoding="UTF-8"?><!DOCTYPEconfigurationPUBLIC"-////DTDConfig3.0//EN""/dtd/mybatis-3-config.dtd"><configuration><environmentsdefault="development"><!--數(shù)據(jù)源配置--><environmentid="development"><transactionManagertype="JDBC"></transactionManager><dataSourcetype="POOLED"><propertyname="driver"value="com.mysql.cj.jdbc.Driver"/><propertyname="url"value="jdbc:mysql://localhost:3306/mybatis_db?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai"/><propertyname="username"value="root"/><propertyname="password"value="password"/></dataSource></environment></environments><!--映射文件配置--><mappers><mapperresource="mapper/UserMapper.xml"/></mappers></configuration>編寫(xiě)映射文件<?xmlversion="1.0"encoding="UTF-8"?><!DOCTYPEmapperPUBLIC"-////DTDMapper3.0//EN""/dtd/mybatis-3-mapper.dtd"><mappernamespace="com.example.mapper.UserMapper"><selectid="getUserById"resultType="com.example.entity.User">select*fromuserwhereid=#{id}</select></mapper>MyBatis支持的數(shù)據(jù)類型INTEGERIntegerVARCHARStringDATEDateTIMESTAMPDate動(dòng)態(tài)SQL語(yǔ)句動(dòng)態(tài)SQL語(yǔ)句是指根據(jù)條件動(dòng)態(tài)生成SQL語(yǔ)句，可以提高代碼的靈活性和可維護(hù)性。IF條件判斷<selectid="getUserByNameAndAge"resultType="com.example.entity.User">select*fromuser<where><iftest="name!=nullandname!=''">name=#{name}</if><iftest="age!=null">andage=#{age}</if></where></select>Choose條件判斷<selectid="getUserByStatus"resultType="com.example.entity.User">select*fromuser<where><choose><whentest="status==1">status=1</when><whentest="status==2">status=2</when><otherwise>statusin(1,2)</otherwise></choose></where></select>Where動(dòng)態(tài)SQL<selectid="getUserByConditions"resultType="com.example.entity.User">select*fromuser<where><iftest="name!=nullandname!=''">name=#{name}</if><iftest="age!=null">andage=#{age}</if></where></select>動(dòng)態(tài)SQL之Trim<selectid="getUserByMultipleConditions"resultType="com.example.entity.User">select*fromuser<where><trimprefix="("suffix=")"prefixOverrides="and"><iftest="name!=nullandname!=''">name=#{name}</if><iftest="age!=null">andage=#{age}</if><iftest="email!=nullandemail!=''">andemail=#{email}</if></trim></where></select>動(dòng)態(tài)SQL之Set<updateid="updateUser"parameterType="com.example.entity.User">updateuser<set><iftest="name!=nullandname!=''">name=#{name},</if><iftest="age!=null">age=#{age},</if><iftest="email!=nullandemail!=''">email=#{email},</if></set>whereid=#{id}</update>MyBatis的參數(shù)傳遞MyBatis支持多種參數(shù)傳遞方式，可以根據(jù)實(shí)際情況選擇合適的方案。單個(gè)參數(shù)傳遞<selectid="getUserById"resultType="com.example.entity.User">select*fromuserwhereid=#{id}</select>多個(gè)參數(shù)傳遞<selectid="getUserByNameAndAge"resultType="com.example.entity.User">select*fromuserwherename=#{name}andage=#{age}</select>使用Map傳參<selectid="getUserByConditions"resultType="com.example.entity.User">select*fromuser<where><iftest="name!=nullandname!=''">name=#{name}</if><iftest="age!=null">andage=#{age}</if></where></select>使用JavaBean傳參<selectid="getUserByConditions"resultType="com.example.entity.User">select*fromuser<where><iftest="name!=nullandname!=''">name=#{name}</if><iftest="age!=null">andage=#{age}</if></where></select>結(jié)果集映射結(jié)果集映射是指將數(shù)據(jù)庫(kù)查詢結(jié)果映射到Java對(duì)象的機(jī)制。一對(duì)一關(guān)聯(lián)關(guān)系<resultMapid="userResultMap"type="com.example.entity.User"><idcolumn="id"property="id"/><resultcolumn="name"property="name"/><resultcolumn="age"property="age"/><associationproperty="address"javaType="com.example.entity.Address"column="address_id"><idcolumn="address_id"property="id"/><resultcolumn="street"property="street"/><resultcolumn="city"property="city"/></association></resultMap>一對(duì)多關(guān)聯(lián)關(guān)系<resultMapid="userResultMap"type="com.example.entity.User"><idcolumn="id"property="id"/><resultcolumn="name"property="name"/><resultcolumn="age"property="age"/><collectionproperty="orders"javaType="java.util.List"ofType="com.example.entity.Order"column="id"><idcolumn="order_id"property="id"/><resultcolumn="product_name"property="productName"/><resultcolumn="price"property="price"/></collection></resultMap>多對(duì)多關(guān)聯(lián)關(guān)系<resultMapid="userResultMap"type="com.example.entity.User"><idcolumn="id"property="id"/><resultcolumn="name"property="name"/><resultcolumn="age"property="age"/><collectionproperty="roles"javaType="java.util.List"ofType="com.example.entity.Role"column="id"><idcolumn="role_id"property="id"/><resultcolumn="role_name"property="roleName"/></collection></resultMap>延遲加載延遲加載是指在需要時(shí)才加載關(guān)聯(lián)對(duì)象，可以提高查詢效率。一級(jí)緩存一級(jí)緩存是SqlSession級(jí)別的緩存，默認(rèn)開(kāi)啟，緩存數(shù)據(jù)只在當(dāng)前SqlSession有效。二級(jí)緩存二級(jí)緩存是Mapper級(jí)別的緩存，默認(rèn)關(guān)閉，需要在SqlMapConfig.xml中配置開(kāi)啟。注解開(kāi)發(fā)MyBatis支持使用注解進(jìn)行開(kāi)發(fā)，簡(jiǎn)化了XML配置。注解之@Select@Select("select*fromuserwhereid=#{id}")UsergetUserById(@Param("id")Integerid);注解之@Insert@Insert("insertintouser(name,age)values(#{name},#{age})")intinsertUser(Useruser);注解之@Update@Update("updateusersetname=#{name},age=#{age}whereid=#{id}")intupdateUser(Useruser);注解之@Delete@Delete("deletefromuserwhereid=#{id}")intdeleteUser(Integerid);注解之@Param@Select("select*fromuserwherename=#{userName}andage=#{userAge}")UsergetUserByNameAndAge(@Param("userName")Stringname,@Param("userAge")Integerage);注解之@ResultMap@Select("select*fromuser")@Results(id="userResultMap",value={@Result(column="id",property="id"),@Result(column="name",property="name"),@Result(column="age",property="age")})List<User>getAllUsers();注解之@One@Select("select*fromuser")@Results(id="userResultMap",value={@Result(column="id",property="id"),@Result(column="name",property="name"),@Result(column="age",property="age"),@Result(property="address",column="address_id",javaType=Address.class,one=@One(select="com.example.mapper.AddressMapper.getAddressById"))})List<User>getAllUsers();注解之@Many@Select("select*fromuser")@Results(id="userResultMap",value={@Result(column="id",property="id"),@Result(column="name",property="name"),@Result(column="age",property="age"),@Result(property="orders",column="id",javaType=List.class,many=@Many(select="com.example.mapper.OrderMapper.getOrdersByUserId"))})List<User>getAllUsers();注解之@CacheNamespace@CacheNamespace(flushInterval=60000,readOnly=true)publicinterfaceUserMapper{//...}整合SpringMyBatis可以與Spring框架進(jìn)行整合，方便管理數(shù)據(jù)源、SqlSessionFactory和Mapper。整合Spring之整合數(shù)據(jù)源<beanid="dataSource"class="org.springframework.jdbc.datasource.DriverManagerDataSource"><propertyname="driverClassName"value="com.mysql.cj.jdb