Java Persistence with MyBatis 3讀書筆記

時間 2019-12-06

標籤 java persistence mybatis 讀書筆記欄目 Java 简体版

原文原文鏈接

第一章 mybatis 簡介

如下內容是本身在看本書時以爲重要的地方記錄下來，一方面本身作個筆記也但願對其餘同行有幫助java

簡介

mybatis: 是一個簡化和實現了Java數據持久層的開源框架愛，抽象和大量的jdbc冗餘代碼，提供簡單的API和數據庫加護mysql

mybatis優勢

消除大量的JDBC冗餘代碼算法
低的學習曲線spring
很好的域傳統數據庫協做sql
接收SQL語句數據庫
提供Spring框架集成apache
提供第三方緩存類庫集成緩存
引入更好的性能安全

mybatis簡單使用

mybatis 配置服務器

<?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. 建立session Factory 類

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();
}
}

建立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>

建立mapper接口

public interface StudentMapper
{
    Student findStudentById(Integer id);
    void insertStudent(Student student);
}

建立會話使用接口

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>
    //加載properties文件
  <properties resource="application.properties">
    <property name="username" value="db_user" />
    <property name="password" value="verysecurepwd" />
  </properties>
  //開啓緩存
  <settings>
    <setting name="cacheEnabled" value="true" />
  </settings>
  
  //別名
  <typeAliases>
    <typeAlias alias="Tutor" type="com.mybatis3.domain.Tutor" />
    <package name="com.mybatis3.domain" />
  </typeAliases>  
  
  //類型處理器，註冊自定義類型
  <typeHandlers>
    <typeHandler handler="com.mybatis3.typehandlers.PhoneTypeHandler" />
    <package name="com.mybatis3.typehandlers" />
  </typeHandlers>
  
  //支持配置多個數據源,設置默認環境爲開發環境
  <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>

以上是一個簡單的基於XML的配置
經過以上XML能夠到全部的配置：

加載properties 文件

直接默認值

<properties resource="application.properties">
      <property name="jdbc.username" value="db_user" />
      <property name="jdbc.password" value="verysecurepwd" />
</properties>

若是文件中定義了jdbc.username，以上配置中的默認值會被覆蓋掉

經過佔位符

<property name="driver" value="${jdbc.driverClassName}" />
  <property name="url" value="${jdbc.url}" />

開啓緩存
配置environments default="development" 實現默認環境，能夠配置不一樣環境
配置多數據庫實現

針對不一樣的數據庫建立不一樣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");

若是不指定環境id，則使用默認的環境建立

數據庫類型配置

UNPOOLED

mybatis會爲每一個數據庫建立錯誤一個新的鏈接，並關閉它。__只適用於小閨蜜數據併發__

POOLED

mybatis建立一個數據庫鏈接池，__開發環境常用__  
默認的數據庫鏈接池實現是經過`org.apache.ibatis.datasource.pooled.PooledDataSource`

JNDI

mybatis從應用服務器配置好的JNDI數據源獲取數據庫鏈接

事務管理

JDBC

是由JDBC事務管理器管理事務。 內部將經過JDBCTransactionFactory建立事務管理

MANAGED

應用服務器負責管理數據庫鏈接生命週期使用。內部使用`ManagedTranscationFactory`類來建立事務管理器

設置別名
因爲在* mapper.xml 文件中resultType和parameterType屬性設置要使用全限定名，可使用別名的形式簡化
```
<typeAliases>
      <typeAlias alias="Student" type="com.mybatis3.domain.Student" />
      <typeAlias alias="Tutor" type="com.mybatis3.domain.Tutor" />
      <package name="com.mybatis3.domain" />
</typeAliases>
```
也能夠不用直接設定別名，能夠設定包，而後系統自動掃描設置一個以類首字母小寫的別名
經過實體類添加註解形式實現
```
@Alias("")
public class Student{

}
```

類型處理器
mubatis對一下類型實現內建處理器：

全部基本數據類型
基本類型的包裹類型(裝箱操做對象類型)
byte[]
java.util.Date
java.sql.Date
java.sql.Time
java.sql.Timestamp
java枚舉類型

建立自定義的類型處理器，處理自定義類型

//PhoneNumber 自定義的類
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));
}
}

別忘了註冊

全局參數設定(一下是默認的，)

<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文件路徑
多種配置形式

<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

經過XML配置形式瞭解了mybatis中的各個配置屬性，經過Java API 的配置形式也能夠實現

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);
        //建立
        sqlSessionFactory = new SqlSessionFactoryBuilder().
        build(configuration);
    }
    catch (Exception e)
    {
        throw new RuntimeException(e);
    }
    return sqlSessionFactory;
}
}

建立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;
    }
    
    //經過JNDI建立  
    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);
        }
    }
    
     
}

自定義mybatis日誌

mybatis 日誌支持

mybatis中針對日誌支持的優先級：

SLF4J
Apache Commons Logging
Log4j 2
Log4j
JDK logging

mybatis 設置日誌

調用一下方式實現

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

經過xml的形式映射有兩種形式：

只有XML映射
- 定義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>

調用

public Student = findStudentById(Integer id){
    SqlSession session = MybatisUtil.geSqlSession();
    try{
        //經過字符串的形式調用
        Student student = sqlSession.selectOne("com.mybatis3.mappers.StudentMapper.findStudentById",id);
    }
}

帶有mapper接口類形式

須要注意的點： __其名空間namespace 應該跟StudentMapper接口的徹底限定名保持一至__, __ id,parameterType,returnType 應該分別和 StudentMapper 接口中的方法名, 參數類型,返回值相對應__

mybatis 提供的的映射語句

mybatis 提供多種不一樣的映射語句:

INSERT
- useGeneratedKeys: 設置自增加
- keyProperty: 主鍵屬性
SELECT
UPDATE
DELETE

mybatis 不一樣映射語句實例：

INSERT

經過自增加設置主鍵

<insert id="insertStudent" parameterType="Student" useGeneratedKeys="true" keyProperty="studId">
    INSERT INTO STUDENTS(NAME, EMAIL, PHONE)
    VALUES(#{name},#{email},#{phone})
</insert>

針對支持序列生成主鍵值

<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>

//使用觸發器  
<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結果集映射規則：

對於 List, Collection, Iterable類型，返回 java.util.ArrayList
對於Map 類型，返回 java.util.HashMap
對於Set 類型：返回 java.util.HashSet
對於SortedSet類型：返回java.util.TreeSet

mybatis 映射關係

一對一映射

方式1：使用點語法進行映射

public class Student
{
   private Integer studId;
   private String name;
   private String email;
   private Address address;        //一個地址對象， 每一個學生對應一個地址  
}

<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>
//使用了左外鏈接來查詢

方式2：使用嵌套結果 ResultMap進行映射

引入其餘文件定義的ResultMap

__使用標籤`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>

查詢語句

<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>

自己內部嵌套

<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查詢語句
每個對應的對象實現本身的查詢語句

<resultMap type="Address" id="AddressResult">
     <id property="addrId" column="addr_id" />
     <result property="street" column="street" />
</resultMap>

//查詢語句
<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>

注意嵌套查詢:經過association 將另外一個對象的查詢語句嵌套進入, 而且此標籤好像只能用於查詢

一對一查詢中內部的對象在數據庫中對應的都是一個Id或者惟一標識值，因此此處底部的嵌套xml中的值都是id屬性的

一對多映射

使用<collection>元素將一對多類型的結果映射到一個對象集合上

使用嵌套對象形式顯示

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>

使用嵌套語句實現

<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 語句查詢會致使 N+1 選擇問. 首先,主查詢將會執行(1 次),對於主查詢返回的每一行,另一個查詢將會被執行(主查詢 N 行,則此查詢 N 次)。對於大型數據庫而言,這會致使不好的性能問題。

動態SQL

mybatis 提供: <if>,<choose>,<where>,<foreach>,<trim> 進行構造動態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>

當if中test條件成立時，纔會添加if中的內容到SQL語句中

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計算<choose> 測試條件的值，且使用第一個值爲true的子句，若是沒有條件爲true，則使用<otherwise> 內的子句。

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

處理枚舉

存儲枚舉名

默認狀況下mybatis支持開箱方式持久化枚舉類型屬性， 其經過`EnumTypeHandler`來處理枚舉類型與Java類型對應  
默認是使用字符串進行存儲的，數據表中對應的是枚舉對應的字符串

存儲枚舉對應的int類型值

須要將枚舉對應的handler修改成如下類

<typeHandler
handler="org.apache.ibatis.type.EnumOrdinalTypeHandler"
javaType="com.mybatis3.domain.Gender"/>

__仍是建議使用默認的形式的，使用順序的若是改變了枚舉對應的順序，數據庫中值就沒法對應上了__

處理 blob類型

默認狀況下，mybatis將CLOB類型的列映射到 java.lang.String類型上，
將BLOB 映射到byte[]類型上

多個參數

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>

使用參數替代

<select id="findAllStudentsByNameEmail" resultMap="StudentResult">
select stud_id, name,email, phone from Students
    where name=#{param1} and email=#{param2}
</select>

緩存

默認狀況下，mybatis開啓一級緩存，對select進行緩存支持。能夠經過<cache>開啓二級緩存
開啓耳機緩存的同時引起的問題：

全部在映射語句文件定義的<select>語句的查詢結果都會被緩存
全部的在映射語句文件定義的<insert>,<update> 和<delete>語句將會刷新緩存
緩存根據最近最少被使用(Least Recently Used,LRU)算法管理
緩存不會被任何形式的基於時間表的刷新(沒有刷新時間間隔),即不支持定時刷新機制
緩存將存儲1024個查詢方法返回的列表或者對象的引用
緩存會被看成一個讀/寫緩存。這是指檢索出的對象不會被共享,而且能夠被調用者安全地修改,不會其餘潛在的調用者或者線程的潛在修改干擾。(即,緩存是線程安全的)

<cache eviction="FIFO" flushInterval="60000" size="512"
readOnly="true"/>

說明:

eviction
- LRU : 最近不多使用
- FIFO : 先進先出
- SOFT : 軟引用
- WEAK : 若引用
flushInterval(定義刷新時間)
size 大小
readOnly 只讀

第四章註解配置SQL映射器

基於註解的一些內容：
- INSERT
- UPDATE
- SELECT
- DELETE

基本使用

@Insert("INSERT INTO STUDENTS(NAME,EMAIL,ADDR_ID, PHONE)
    VALUES(#{name},#{email},#{address.addrId},#{phone})")
  //經過如下註解實現主鍵 
  @Options(useGeneratedKeys = true, keyProperty = "studId")

//經過此註解爲任意SQL語句指定主鍵值(使用此註解生成主鍵)
@SelectKey(statement="SELECT STUD_ID_SEQ.NEXTVAL FROM DUAL",
keyProperty="studId", resultType=int.class, before=true)

//使用觸發器生成
@SelectKey(statement="SELECT STUD_ID_SEQ.CURRVAL FROM DUAL",
keyProperty="studId", resultType=int.class, before=false)


//結果集映射  
@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")
})

一對一映射

嵌套sql語句形式

//使用嵌套select 語句實現
@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"))
})

嵌套對象

此種方式並無註解形式的實現 ，能夠經過在XML中定義映射`resultMap`集，而後經過`@ResultMap`進行映射

@ResultMap("com.mybatis3.mappers.StudentMapper.
               StudentWithAddressResult")

一對多映射
一樣的只有嵌套SQL的形式

@Result(property = "courses", column = "tutor_id",
many = @Many(select = "com.mybatis3.mappers.TutorMapper.
findCoursesByTutorId"))

遇到的問題

結果集不能重用，由於沒法賦予id，因此沒法重用，哪怕相同都必須重寫寫
能夠經過一個xml進行映射

<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>

    //經過此種方式解決沒法重用的問題
 @Select("SELECT * FROM STUDENTS WHERE STUD_ID=#{studId}")
      @ResultMap("com.mybatis3.mappers.StudentMapper.StudentResult")

針對動態SQL經過工具類的方式生成SQL語句

return new SQL()
{
    {
        SELECT("tutor_id as tutorId, name, email");
        FROM("tutors");
         WHERE("tutor_id=" + tutorId);
      }
} .toString();
}

動態SQL映射

建立動態SQL映射類

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();
}

添加動態SQL註解到方法上

@SelectProvider(type=TutorDynaSqlProvider.class, method="findTutorByIdSql")
Tutor findTutorById(int tutorId);

第五章 spring 集成

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>

經過此種方式配置就能夠引用sqlSession

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"> 
    <property name="basePackage" value="com.mybatis3.mappers" />
</bean>

經過以上的方式掃描包中的映射器Mapper接口，並自動註冊

mybatis關於mapper掃描有兩種方式：

* 使用XML形式  
    ` <mybatis:scan base-package="com.mybatis3.mappers" />`
* 使用`@MapperScan`註解

很是感謝針對本書翻譯的工做者

相關標籤/搜索

每日一句

每一个你不满意的现在，都有一个你没有努力的曾经。

Java Persistence with MyBatis 3讀書筆記

第一章 mybatis 簡介

簡介

mybatis優勢

mybatis簡單使用

第二章 mybatis 配置

使用XML配置

使用Java 配置

自定義mybatis日誌

mybatis 日誌支持

mybatis 設置日誌

第三章 XML配置SQL映射器

mybatis 提供的的映射語句

mybatis 不一樣映射語句實例：

mybatis結果集映射規則：

mybatis 映射關係

一對一映射

一對多映射

動態SQL

1. if

choose, when, otherwise

where

trim

foreach

mybatis Other

處理枚舉

處理 blob類型

多個參數

緩存

第四章 註解配置SQL映射器

第五章 spring 集成

第四章註解配置SQL映射器