第一章 mybatis 简介
以下内容是自己在看本书时觉得重要的地方记录下来，一方面自己做个笔记也希望对其他同行有帮助
简介
mybatis: 是一个简化和实现了Java数据持久层的开源框架爱，抽象和大量的jdbc冗余代码，提供简单的API和数据库加护
mybatis优点
消除大量的JDBC冗余代码
低的学习曲线
很好的域传统数据库协作
接收SQL语句
提供Spring框架集成
提供第三方缓存类库集成
引入更好的性能
mybatis简单使用
-
mybatis 配置
<?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> <typeAliases> <typeAlias alias="Student" type="com.mybatis3.domain.Student" /> </typeAliases> <environments default="development"> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver" /> <property name="url" value="jdbc:mysql://localhost:3306/test" /> <property name="username" value="root" /> <property name="password" value="admin" /> </dataSource> </environment> </environments> <mappers> <mapper resource="com/mybatis3/mappers/StudentMapper.xml" /> </mappers> </configuration>
0.1. 创建session Factory 类
package com.mybatis3.util;
import java.io.*;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.*;
public class MyBatisSqlSessionFactory
{
private static SqlSessionFactory sqlSessionFactory;
public static SqlSessionFactory getSqlSessionFactory()
{
if(sqlSessionFactory == null)
{
InputStream inputStream;
try
{
inputStream = Resources.
getResourceAsStream("mybatis-config.xml");
sqlSessionFactory = new
SqlSessionFactoryBuilder().build(inputStream);
}
catch (IOException e)
{
throw new RuntimeException(e.getCause());
}
}
return sqlSessionFactory;
}
public static SqlSession openSession()
{
return getSqlSessionFactory().openSession();
}
}-
创建xml映射
<select id="findStudentById" parameterType="int" resultType="Student"> SELECT STUD_ID AS studId, NAME, EMAIL, DOB FROM STUDENTS WHERE STUD_ID=#{Id} </select> <insert id="insertStudent" parameterType="Student"> INSERT INTO STUDENTS(STUD_ID,NAME,EMAIL,DOB) VALUES(#{studId},#{name},#{email},#{dob}) </insert> -
创建mapper接口
public interface StudentMapper { Student findStudentById(Integer id); void insertStudent(Student student); } -
创建会话使用接口
SqlSession session = getSqlSessionFactory().openSession(); StudentMapper mapper = session.getMapper(StudentMapper.class); // Select Student by Id Student student = mapper.selectStudentById(1); //To insert a Student record mapper.insertStudent(student);
第二章 mybatis 配置
使用XML配置
<?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>
//加载properties文件
<properties resource="application.properties">
<property name="username" value="db_user" />
<property name="password" value="verysecurepwd" />
</properties>
//开启缓存
<settings>
<setting name="cacheEnabled" value="true" />
</settings>
//别名
<typeAliases>
<typeAlias alias="Tutor" type="com.mybatis3.domain.Tutor" />
<package name="com.mybatis3.domain" />
</typeAliases>
//类型处理器，注册自定义类型
<typeHandlers>
<typeHandler handler="com.mybatis3.typehandlers.PhoneTypeHandler" />
<package name="com.mybatis3.typehandlers" />
</typeHandlers>
//支持配置多个数据源,设置默认环境为开发环境
<environments default="development">
<environment id="development">
<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>
<environment id="production">
<transactionManager type="MANAGED" />
<dataSource type="JNDI">
<property name="data_source" value="java:comp/jdbc/MyBatisDemoDS" />
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/mybatis3/mappers/StudentMapper.xml" />
<mapper url="file:///D:/mybatisdemo/mappers/TutorMapper.xml" />
<mapper class="com.mybatis3.mappers.TutorMapper" />
</mappers>
</configuration>以上是一个简单的基于XML的配置
通过以上XML可以到所有的配置：
-
加载properties 文件
-
直接默认值
<properties resource="application.properties"> <property name="jdbc.username" value="db_user" /> <property name="jdbc.password" value="verysecurepwd" /> </properties>如果文件中定义了
jdbc.username，以上配置中的默认值会被覆盖掉 -
通过占位符
<property name="driver" value="${jdbc.driverClassName}" /> <property name="url" value="${jdbc.url}" />
-
开启缓存
配置
environments default="development"实现默认环境 ，可以配置不同环境配置多数据库实现
-
针对不同的数据库创建不同sessionFactory
InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml"); SqlSessionFactory defaultSqlSessionFactory = new SqlSessionFactoryBuilder(). build(inputStream); SqlSessionFactory cartSqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStre am, "shoppingcart"); reportSqlSessionFactory = new SqlSessionFactoryBuilder(). build(inputStream, "reports");如果不指定环境id，则使用默认的环境创建
-
数据库类型配置
-
UNPOOLEDmybatis会为每个数据库创建错误一个新的连接，并关闭它。__只适用于小闺蜜数据并发__ -
POOLEDmybatis创建一个数据库连接池，__开发环境经常使用__ 默认的数据库连接池实现是通过`org.apache.ibatis.datasource.pooled.PooledDataSource` -
JNDImybatis从应用服务器配置好的JNDI数据源获取数据库连接
-
-
事务管理
-
JDBC是由JDBC事务管理器管理事务。 内部将通过JDBCTransactionFactory创建事务管理 -
MANAGED应用服务器负责管理数据库连接生命周期使用。内部使用`ManagedTranscationFactory`类来创建事务管理器
-
-
设置别名
由于在* mapper.xml文件中resultType和parameterType属性设置要使用全限定名，可以使用别名的形式简化<typeAliases> <typeAlias alias="Student" type="com.mybatis3.domain.Student" /> <typeAlias alias="Tutor" type="com.mybatis3.domain.Tutor" /> <package name="com.mybatis3.domain" /> </typeAliases>也可以不用直接设定别名，可以设定包，然后系统自动扫描设置一个以类首字母小写的别名
通过实体类添加注解形式实现@Alias("") public class Student{ } -
类型处理器
mubatis对一下类型实现內建处理器 ：所有基本数据类型
基本类型的包裹类型(装箱操作对象类型)
byte[]
java.util.Date
java.sql.Date
java.sql.Time
java.sql.Timestamp
java枚举类型
创建自定义的类型处理器，处理自定义类型
//PhoneNumber 自定义的类 public class PhoneTypeHandler extends BaseTypeHandler<PhoneNumber> { @Override public void setNonNullParameter(PreparedStatement ps, int i, PhoneNumber parameter, JdbcType jdbcType) throws SQLException { ps.setString(i, parameter.getAsString()); } public PhoneNumber getNullableResult(ResultSet rs, String columnName) throws SQLException { return new PhoneNumber(rs.getString(columnName)); } public PhoneNumber getNullableResult(ResultSet rs, int columnIndex) throws SQLException { return new PhoneNumber(rs.getString(columnIndex)); } }别忘了注册
-
全局参数设定(一下是默认的，)
<settings> <setting name="cacheEnabled" value="true" /> <setting name="lazyLoadingEnabled" value="true" /> <setting name="multipleResultSetsEnabled" value="true" /> <setting name="useColumnLabel" value="true" /> <setting name="useGeneratedKeys" value="false" /> <setting name="autoMappingBehavior" value="PARTIAL" /> <setting name="defaultExecutorType" value="SIMPLE" /> <setting name="defaultStatementTimeout" value="25000" /> <setting name="safeRowBoundsEnabled" value="false" /> <setting name="mapUnderscoreToCamelCase" value="false" /> <setting name="localCacheScope" value="SESSION" /> <setting name="jdbcTypeForNull" value="OTHER" /> <setting name="lazyLoadTriggerMethods" value="equals,clone,hashCode ,toString" /> </settings> -
配置mappers映射xml文件路径
多种配置形式<mappers> <mapper resource="com/mybatis3/mappers/StudentMapper.xml" /> <mapper url="file:///D:/mybatisdemo/app/mappers/TutorMapper.xml" /> <mapper class="com.mybatis3.mappers.TutorMapper" /> <package name="com.mybatis3.mappers" /> </mappers>
使用Java 配置
通过XML配置形式了解了mybatis中的各个配置属性， 通过Java API 的配置形式也可以实现
public class MybatisConfig{
public static SqlSessionFactory getSqlSessionFactory()
{
SqlSessionFactory sqlSessionFactory = null;
try
{
DataSource dataSource = DataSourceFactory.getDataSource();
TransactionFactory transactionFactory = new
JdbcTransactionFactory();
Environment environment = new Environment("development",
transactionFactory, dataSource);
Configuration configuration = new Configuration(environment);
configuration.getTypeAliasRegistry().registerAlias("student",
Student.class);
configuration.getTypeHandlerRegistry().register(PhoneNumber.
class, PhoneTypeHandler.class);
configuration.addMapper(StudentMapper.class);
//创建
sqlSessionFactory = new SqlSessionFactoryBuilder().
build(configuration);
}
catch (Exception e)
{
throw new RuntimeException(e);
}
return sqlSessionFactory;
}
}创建datasource
public class DataSourceFactory
{
public static DataSource getDataSource(){
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/mybatisdemo";
String username = "root";
String password = "admin";
PooledDataSource dataSource = new PooledDataSource(driver, url,
username, password);
return dataSource;
}
//通过JNDI创建
public static DataSource getDataSource(){
String jndiName = "java:comp/env/jdbc/MyBatisDemoDS";
try{
InitialContext ctx = new InitialContext();
DataSource dataSource = (DataSource) ctx.lookup(jndiName);
return dataSource;
}catch(NamingException e){
throw new RuntimeException(e);
}
}
}自定义mybatis日志
mybatis 日志支持
mybatis中针对日志支持的优先级：
SLF4J
Apache Commons Logging
Log4j 2
Log4j
JDK logging
mybatis 设置日志
调用一下方式实现
org.apache.ibatis.logging.LogFactory.useSlf4jLogging();
org.apache.ibatis.logging.LogFactory.useLog4JLogging();
org.apache.ibatis.logging.LogFactory.useLog4J2Logging();
org.apache.ibatis.logging.LogFactory.useJdkLogging();
org.apache.ibatis.logging.LogFactory.useCommonsLogging();
org.apache.ibatis.logging.LogFactory.useStdOutLogging();第三章 XML配置SQL映射器
通过xml的形式映射有两种形式：
-
只有XML映射
定义xml映射文件
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis3.mappers.StudentMapper">
<select id="findStudentById" parameterType="int" resultType="Student"> select stud_id as studId, name, email, dob
from Students where stud_id=#{studId}
</select>
</mapper>-
调用
public Student = findStudentById(Integer id){ SqlSession session = MybatisUtil.geSqlSession(); try{ //通过字符串的形式调用 Student student = sqlSession.selectOne("com.mybatis3.mappers.StudentMapper.findStudentById",id); } } -
带有mapper接口类形式
需要注意的点： __其名空间namespace 应该跟StudentMapper接口的完全限定名保持一至__, __ id,parameterType,returnType 应该分别和 StudentMapper 接口中的方法名, 参数类型,返回值相对应__
mybatis 提供的的映射语句
mybatis 提供多种不同的映射语句:
-
INSERT
useGeneratedKeys: 设置自增长keyProperty: 主键属性
SELECT
UPDATE
DELETE
mybatis 不同映射语句实例：
-
INSERT
-
通过自增长设置主键
<insert id="insertStudent" parameterType="Student" useGeneratedKeys="true" keyProperty="studId"> INSERT INTO STUDENTS(NAME, EMAIL, PHONE) VALUES(#{name},#{email},#{phone}) </insert> -
针对支持序列生成主键值
<insert id="insertStudent" parameterType="Student"> <selectKey keyProperty="studId" resultType="int" order="BEFORE"> SELECT ELEARNING.STUD_ID_SEQ.NEXTVAL FROM DUAL </selectKey> INSERT INTO STUDENTS(STUD_ID,NAME,EMAIL, PHONE) VALUES(#{studId},#{name},#{email},#{phone}) </insert> //使用触发器 <insert id="insertStudent" parameterType="Student"> INSERT INTO STUDENTS(NAME,EMAIL, PHONE) VALUES(#{name},#{email},#{phone}) <selectKey keyProperty="studId" resultType="int" order="AFTER"> SELECT ELEARNING.STUD_ID_SEQ.CURRVAL FROM DUAL </selectKey> </insert>
-
mybatis结果集映射规则：
对于 List, Collection, Iterable类型，返回 java.util.ArrayList
对于Map 类型，返回 java.util.HashMap
对于Set 类型： 返回 java.util.HashSet
对于SortedSet类型： 返回java.util.TreeSet
mybatis 映射关系
一对一映射
方式1： 使用点语法进行映射
public class Student
{
private Integer studId;
private String name;
private String email;
private Address address; //一个地址对象， 每个学生对应一个地址
}
<resultMap type="Student" id="StudentWithAddressResult">
<id property="studId" column="stud_id" />
<result property="name" column="name" />
<result property="email" column="email" />
<result property="phone" column="phone" />
<result property="address.addrId" column="addr_id" />
<result property="address.street" column="street" />
<result property="address.city" column="city" />
<result property="address.state" column="state" />
<result property="address.zip" column="zip" />
<result property="address.country" column="country" />
</resultMap>
<select id="selectStudentWithAddress" parameterType="int"
resultMap="StudentWithAddressResult">
SELECT STUD_ID, NAME, EMAIL, A.ADDR_ID, STREET, CITY, STATE,
ZIP, COUNTRY
FROM STUDENTS S LEFT OUTER JOIN ADDRESSES A ON S.ADDR_ID=A.ADDR_ID
WHERE STUD_ID=#{studId}
</select>
//使用了左外连接来查询-
方式2： 使用嵌套结果
ResultMap进行映射-
引入其他文件定义的
ResultMap__使用标签`association` 引入__<resultMap type="Address" id="AddressResult"> <id property="addrId" column="addr_id" /> <result property="street" column="street" /> <result property="city" column="city" /> </resultMap> <resultMap type="Student" id="StudentWithAddressResult"> <id property="studId" column="stud_id" /> <result property="name" column="name" /> <result property="email" column="email" /> <association property="address" resultMap="AddressResult" /> </resultMap>查询语句<select id="findStudentWithAddress" parameterType="int" resultMap="StudentWithAddressResult"> SELECT STUD_ID, NAME, EMAIL, A.ADDR_ID, STREET, CITY, STATE, ZIP, COUNTRY FROM STUDENTS S LEFT OUTER JOIN ADDRESSES A ON S.ADDR_ID=A.ADDR_ID WHERE STUD_ID=#{studId} </select> -
本身内部嵌套
<resultMap type="Student" id="StudentWithAddressResult"> <id property="studId" column="stud_id" /> <result property="name" column="name" /> <result property="email" column="email" /> <association property="address" javaType="Address"> <id property="addrId" column="addr_id" /> <result property="street" column="street" /> <result property="city" column="city" /> <result property="state" column="state" /> <result property="zip" column="zip" /> <result property="country" column="country" /> </association> </resultMap>
-
-
方式3： 使用其那套select查询语句
每一个对应的对象实现自己的查询语句<resultMap type="Address" id="AddressResult"> <id property="addrId" column="addr_id" /> <result property="street" column="street" /> </resultMap> //查询语句 <select id="findAddressById" parameterType="int" resultMap="AddressResult"> SELECT * FROM ADDRESSES WHERE ADDR_ID=#{id} </select> <resultMap type="Student" id="StudentWithAddressResult"> <id property="studId" column="stud_id" /> <association property="address" column="addr_id" select="findAddressById" /> </resultMap> <select id="findStudentWithAddress" parameterType="int" resultMap="StudentWithAddressResult"> SELECT * FROM STUDENTS WHERE STUD_ID=#{Id} </select>注意嵌套查询:通过
association将另一个对象的查询语句嵌套进入, 并且此标签好像只能用于查询
一对一查询中内部的对象在数据库中对应的都是一个Id或者唯一标识值，所以此处底部的嵌套xml中的值都是id属性的
一对多映射
使用<collection>元素将 一对多类型的结果 映射到 一个对象集合上
使用嵌套对象形式显示
public class Tutor
{
private Integer tutorId;
private String name;
private String email;
private Address address;
private List<Course> courses;
/ setters & getters
}
<resultMap type="Tutor" id="TutorResult">
<id column="tutor_id" property="tutorId" />
<result column="tutor_name" property="name" />
<result column="email" property="email" />
<collection property="courses" resultMap="CourseResult" />
</resultMap>
<select id="findTutorById" parameterType="int"
resultMap="TutorResult">
SELECT T.TUTOR_ID, T.NAME AS TUTOR_NAME, EMAIL, C.COURSE_ID,
C.NAME, DESCRIPTION, START_DATE, END_DATE
FROM TUTORS T LEFT OUTER JOIN ADDRESSES A ON T.ADDR_ID=A.ADDR_ID
LEFT OUTER JOIN COURSES C ON T.TUTOR_ID=C.TUTOR_ID
WHERE T.TUTOR_ID=#{tutorId}
</select>
使用嵌套语句实现
<resultMap type="Tutor" id="TutorResult">
<id column="tutor_id" property="tutorId" />
<result column="tutor_name" property="name" />
<result column="email" property="email" />
<association property="address" resultMap="AddressResult" />
<collection property="courses" column="tutor_id" select="findCoursesByTutor" />
</resultMap>
<select id="findTutorById" parameterType="int" resultMap="TutorResult">
SELECT T.TUTOR_ID, T.NAME AS TUTOR_NAME, EMAIL
FROM TUTORS T WHERE T.TUTOR_ID=#{tutorId}
</select>
<select id="findCoursesByTutor" parameterType="int" resultMap="CourseResult">
SELECT * FROM COURSES WHERE TUTOR_ID=#{tutorId}
</select>
注意: 嵌套 Select 语句查询会导致 N+1 选择问. 首先,主查询将会执行(1 次),对于主 查询返回的每一行,另外一个查询将会被执行(主查询 N 行,则此查询 N 次)。对于 大型数据库而言,这会导致很差的性能问题。
动态SQL
mybatis 提供: <if>,<choose>,<where>,<foreach>,<trim> 进行构造动态SQL
1. if
<select id="searchCourses" parameterType="hashmap" resultMap="CourseResult"></select>
SELECT * FROM COURSES
WHERE TUTOR_ID= #{tutorId}
<if test="courseName != null">
AND NAME LIKE #{courseName}
</if>
</select>当if中test条件成立时， 才会添加if中的内容到SQL语句中
choose, when, otherwise
<select id="searchCourses" parameterType="hashmap" resultMap="CourseResult">
SELECT * FROM COURSES
<choose>
<when test="searchBy == 'Tutor'">
WHERE TUTOR_ID= #{tutorId}
</when>
<when test="searchBy == 'CourseName'">
WHERE name like #{courseName}
</when>
<otherwise>
WHERE TUTOR start_date >= now()
</otherwise>
</choose>
</select>__mybatis计算<choose> 测试条件的值，且使用第一个值为true的子句， 如果没有条件为true，则使用<otherwise> 内的子句。
where
<select id="searchCourses" parameterType="hashmap"
resultMap="CourseResult">
SELECT * FROM COURSES
<where>
<if test=" tutorId != null ">
TUTOR_ID= #{tutorId}
</if>
<if test="courseName != null">
AND name like #{courseName}
</if>
<if test="startDate != null">
AND start_date >= #{startDate}
</if>
<if test="endDate != null">
AND end_date <= #{endDate}
</if>
</where>
</select>trim
<select id="searchCourses" parameterType="hashmap" resultMap="CourseResult">
SELECT * FROM COURSES
<trim prefix="WHERE" prefixOverrides="AND | OR">
<if test=" tutorId != null ">
TUTOR_ID= #{tutorId}
</if>
<if test="courseName != null">
AND name like #{courseName}
</if>
</trim>
</select>
foreach
<select id="searchCoursesByTutors" parameterType="map"
resultMap="CourseResult">
SELECT * FROM COURSES
<if test="tutorIds != null">
<where>
<foreach item="tutorId" collection="tutorIds">
OR tutor_id=#{tutorId}
</foreach>
</where>
</if>
</select>mybatis Other
处理枚举
-
存储枚举名
默认情况下mybatis支持开箱方式持久化枚举类型属性， 其通过`EnumTypeHandler`来处理枚举类型与Java类型对应 默认是使用字符串进行存储的，数据表中对应的是枚举对应的字符串 -
存储枚举对应的int类型值
需要将枚举对应的handler修改为以下类<typeHandler handler="org.apache.ibatis.type.EnumOrdinalTypeHandler" javaType="com.mybatis3.domain.Gender"/>__还是建议使用默认的形式的，使用顺序的如果改变了枚举对应的顺序，数据库中值就无法对应上了__
处理 blob类型
默认情况下，mybatis将CLOB类型的列映射到 java.lang.String类型上，
将BLOB 映射到byte[]类型上
多个参数
-
使用map形式引入
<select id="findAllStudentsByNameEmail" resultMap="StudentResult" parameterType="map"> select stud_id, name,email, phone from Students where name=#{name} and email=#{email} </select> -
使用参数替代
<select id="findAllStudentsByNameEmail" resultMap="StudentResult"> select stud_id, name,email, phone from Students where name=#{param1} and email=#{param2} </select>
缓存
默认情况下，mybatis开启一级缓存，对select进行缓存支持。 可以通过<cache>开启二级缓存
开启耳机缓存的同时引发的问题：
所有在映射语句文件定义的<select>语句的查询结果都会被缓存
所有的在映射语句文件定义的<insert>,<update> 和<delete>语句将会刷新缓存
缓存根据最近最少被使用(Least Recently Used,LRU)算法管理
缓存不会被任何形式的基于时间表的刷新(没有刷新时间间隔),即不支持定时刷新机制
缓存将存储1024个 查询方法返回的列表或者对象的引用
缓存会被当作一个读/写缓存。这是指检索出的对象不会被共享,并且可以被调用者安全地修改,不会其他潜 在的调用者或者线程的潜在修改干扰。(即,缓存是线程安全的)
<cache eviction="FIFO" flushInterval="60000" size="512"
readOnly="true"/>说明:
-
eviction
LRU : 最近很少使用
FIFO : 先进先出
SOFT : 软引用
WEAK : 若引用
flushInterval(定义刷新时间)
size 大小
readOnly 只读
第四章 注解配置SQL映射器
-
基于注解的一些内容：
INSERTUPDATESELECTDELETE
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基本使用
@Insert("INSERT INTO STUDENTS(NAME,EMAIL,ADDR_ID, PHONE) VALUES(#{name},#{email},#{address.addrId},#{phone})") //通过以下注解实现主键 @Options(useGeneratedKeys = true, keyProperty = "studId") //通过此注解为任意SQL语句指定主键值(使用此注解生成主键) @SelectKey(statement="SELECT STUD_ID_SEQ.NEXTVAL FROM DUAL", keyProperty="studId", resultType=int.class, before=true) //使用触发器生成 @SelectKey(statement="SELECT STUD_ID_SEQ.CURRVAL FROM DUAL", keyProperty="studId", resultType=int.class, before=false) //结果集映射 @Results( { @Result(id = true, column = "stud_id", property = "studId"), @Result(column = "name", property = "name"), @Result(column = "email", property = "email"), @Result(column = "addr_id", property = "address.addrId") })-
一对一映射
嵌套sql语句形式
//使用嵌套select 语句实现 @Results( { @Result(id = true, column = "stud_id", property = "studId"), @Result(column = "name", property = "name"), @Result(column = "email", property = "email"), @Result(property = "address", column = "addr_id", one = @One(select = "com.mybatis3.mappers.StudentMapper. findAddressById")) })-
嵌套对象
此种方式并没有注解形式的实现 ，可以通过在XML中定义映射`resultMap`集，然后通过`@ResultMap`进行映射@ResultMap("com.mybatis3.mappers.StudentMapper. StudentWithAddressResult")
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一对多映射
同样的只有嵌套SQL的形式@Result(property = "courses", column = "tutor_id", many = @Many(select = "com.mybatis3.mappers.TutorMapper. findCoursesByTutorId"))
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遇到的问题
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结果集不能重用，因为无法赋予id， 所以无法重用，哪怕相同都必须重写写
可以通过一个xml进行映射<mapper namespace="com.mybatis3.mappers.StudentMapper"> <resultMap type="Student" id="StudentResult"> <id property="studId" column="stud_id" /> <result property="name" column="name" /> <result property="email" column="email" /> <result property="phone" column="phone" /> </resultMap> </mapper> //通过此种方式解决无法重用的问题 @Select("SELECT * FROM STUDENTS WHERE STUD_ID=#{studId}") @ResultMap("com.mybatis3.mappers.StudentMapper.StudentResult") -
针对动态SQL通过工具类的方式生成SQL语句
return new SQL() { { SELECT("tutor_id as tutorId, name, email"); FROM("tutors"); WHERE("tutor_id=" + tutorId); } } .toString(); }
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动态SQL映射
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创建动态SQL映射类
public class TutorDynaSqlProvider { public String findTutorByIdSql(int tutorId) { return "SELECT TUTOR_ID AS tutorId, NAME, EMAIL FROM TUTORS WHERE TUTOR_ID=" + tutorId; } }public String findTutorByNameAndEmailSql(Map<String, Object> map) { String name = (String) map.get("param1"); String email = (String) map.get("param2"); //you can also get those values using 0,1 keys //String name = (String) map.get("0"); //String email = (String) map.get("1"); return new SQL() { { SELECT("tutor_id as tutorId, name, email"); FROM("tutors"); WHERE("name=#{name} AND email=#{email}"); } } .toString(); } -
添加动态SQL注解到方法上
@SelectProvider(type=TutorDynaSqlProvider.class, method="findTutorByIdSql") Tutor findTutorById(int tutorId);
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第五章 spring 集成
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配置mybatis beans
`applicationContext.xml` 中添加
<beans>
<bean id="dataSource" class="org.springframework.jdbc.datasource. DriverManagerDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/elearning" />
<property name="username" value="root" />
<property name="password" value="admin" />
</bean>
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="typeAliases" value="com.mybatis3.domain.Student, com.mybatis3.domain.Tutor" /> <property name="typeAliasesPackage" value="com.mybatis3.domain" />
<property name="typeHandlers" value="com.mybatis3.typehandlers.PhoneTypeHandler" />
<property name="typeHandlersPackage" value="com.mybatis3.typehandlers" />
<property name="mapperLocations" value="classpath*:com/mybatis3/**/*.xml" />
<property name="configLocation" value="WEB-INF/mybatisconfig.xml" />
</bean>
</beans>
<bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">
<constructor-arg index="0" ref="sqlSessionFactory" />
</bean>通过此种方式配置就可以引用sqlSession
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.mybatis3.mappers" />
</bean>通过以上的方式扫描包中的映射器Mapper接口， 并自动注册
mybatis关于mapper扫描有两种方式 ：
* 使用XML形式
` <mybatis:scan base-package="com.mybatis3.mappers" />`
* 使用`@MapperScan`注解
非常感谢针对本书翻译的工作者
java
mysql
**粗体** _斜体_ [链接](http://example.com) `代码` - 列表 > 引用。你还可以使用@来通知其他用户。