一小时迅速入门Mybatis之实体类别名与多参数 动态SQL

时间：2022-09-27 14:56:54

一、说明

前边两篇腿已经迈进门了，这篇开始讲实体类别名、多参数、动态SQL等

二、开搞

数据库表

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DROP TABLE IF EXISTS `test`;
CREATE TABLE `test`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `name` varchar(200) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  `salary` decimal(10, 2) NOT NULL,
  `age` int(11) NULL DEFAULT NULL,
  `city` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `job` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 43 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
 
-- ----------------------------
-- Records of test
-- ----------------------------
INSERT INTO `test` VALUES (1, '小明', 40000.00, 18, '北京', '程序猿');
INSERT INTO `test` VALUES (2, '小强', 50000.00, 19, '南京', '程序汪');
INSERT INTO `test` VALUES (3, '小月月', 50000.00, 20, '天津', '程序狗');
INSERT INTO `test` VALUES (4, '小月鸟', 40000.00, 21, '广州', '程序屌丝');

2.1 实体类别名

2.1.1 第一种方式

1.创建实体类
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package entity;
 
import java.math.BigDecimal;
 
/**
 * 一个生活在互联网底层，做着增删改查的码农,不谙世事的造作
 * @create 2021-08-25 22:05
 */
 
public class TestEntity {
    private  Long id;
    private String name;
    private BigDecimal salary;
    private Integer age;
    private String city;
    private String job;
    // get set方法省略  IntelliJ IDEA  生成快捷键是Alt+Inert 选择Getter and Setter
    // toString 方法省略   IntelliJ IDEA  生成快捷键是Alt+Inert 选择 toString
}
2.创建XML

mybatis-config.xml

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<?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>
    <!--这里一定注意顺序 -->
    <typeAliases>
        <typeAlias type="entity.TestEntity" alias="testEntity"/>
    </typeAliases>
    <!--省略environments 看前2篇 -->
     <!--省略扫描 看前2篇-->
</configuration>

配置文件顺序要这样配置：

<properties>...</properties>
<settings>...</settings>
<typeAliases>...</typeAliases>
<typeHandlers>...</typeHandlers>
<objectFactory>...</objectFactory>
<objectWrapperFactory>...</objectWrapperFactory>
<plugins>...</plugins>
<environments>...</environments>
<databaseIdProvider>...</databaseIdProvider>
<mappers>...</mappers>

3.使用别名
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<!--根据主键查询-->
<select id="get" resultType="testEntity">
    select * from test where id = #{id}
</select>
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public class TestMain {
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        try (SqlSession session = sqlSessionFactory.openSession()) {
            // 通过sesson获取Mapper 这个Mapper会编程Mybatis的代理Mapper
            TestMapper mapper = session.getMapper(TestMapper.class);
            System.out.println(mapper);
            // 查询数据
            TestEntity testEntity = mapper.get(1L);
            System.out.println(testEntity);
        }
    }
}

2.1.2 第二种方式

扫描包路径 mybatis-config.xml

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<?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>
  <!--扫描包路径-->
    <typeAliases>
        <package name="entity"/>
    </typeAliases>
    <!--省略environments 看前2篇 -->
     <!--省略扫描 看前2篇-->
</configuration>

用扫描包路径的方式，实体类别名默认就是java类首字母小写

例如：TestEntity --> testEntity

还可以注解指定：

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@Alias("testEntityxxoo")
public class TestEntity {
    // 其他省略
}

如果写了注解@Alias 别名就不是”testEntity”了 ，就变成”testEntityxxoo“

2.1.3 mybatis默认别名

 

  映射类型
_byte byte
_long long
_short short
_int int
_integer int
_double double
_float float
_boolean boolean
string String
byte Byte
long Long
short Short
int Integer
integer Integer
double Double
float Float
boolean Boolean
date Date
decimal BigDecimal
bigdecimal BigDecimal
object Object
map Map
hashmap HashMap
list List
arraylist ArrayList
collection Collection
iterator Iterator

 

2.2 插入数据返回自增主键

2.2.1方式一

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<!--增加-->
<insert id="save" useGeneratedKeys="true" keyProperty="id">
    INSERT INTO `test`( `name`, `salary`) VALUE (#{name}, #{salary});
</insert>
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public class TestMain {
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        try (SqlSession session = sqlSessionFactory.openSession()) {
            // 通过sesson获取Mapper 这个Mapper会编程Mybatis的代理Mapper
            TestMapper mapper = session.getMapper(TestMapper.class);
            // 测试id是否到了实体类里边
            TestEntity testEntity = new TestEntity();
            testEntity.setName("小鸭子");
            testEntity.setSalary(new BigDecimal(100000));
            mapper.save(testEntity);
            System.out.println("主键:"+testEntity.getId());
        }
    }
}

输出结果：

一小时迅速入门Mybatis之实体类别名与多参数 动态SQL

主键不是直接返回的，而是把主键值设置到插入的对象里的

2.2.2 方式二

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<!--增加-->
<insert id="save">
    <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Long">
        SELECT LAST_INSERT_ID()
    </selectKey>
    INSERT INTO `test`(`id`, `name`, `salary`) VALUE (#{id},#{name}, #{salary})
</insert>

2.3 多参数

2.3.1 一个参数

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// 根据主键查询
TestEntity get(Long id);
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<!--根据主键查询-->
<select id="get" resultType="testEntity">
    select * from test where id = #{id}
</select>
<select id="get" resultType="testEntity">
    select * from test where id = #{xx}
</select>
<select id="get" resultType="testEntity">
    select * from test where id = #{oo}
</select>
<select id="get" resultType="testEntity">
    select * from test where id = #{aaabbb}
</select>

如果只有一个参数，并且参数类型是Java基础类型或String类型，那么使用这个参数的时候

#{xxoo} xxoo可以是任意字符 与方法输入参数名称无关

上边例子中：id、xx、oo、aaabbb 都可以使用 ，但是哈，我们一般见名知意，传递的什么参数(id),我们xml就用#{传递的参数} 这不是必须但可以遵循这个规范

2.3.2 多个参数 之实体类

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// 新增
void save(TestEntity testEntity);
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<!--增加-->
<insert id="save">
    INSERT INTO `test`(`name`, `salary`) VALUE (#{name}, #{salary})
</insert>

这个很容易明白，实体类参数叫什么 这里#{}里边就用什么

2.3.3 多个参数之@Param注解

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// 根据名称模糊查询
List<TestEntity> listByNameAndAge(@Param("name") String name,@Param("age") Integer age);
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<!--根据名称和年龄查寻-->
<select id="listByNameAndAge" resultType="testentity">
    select * from test
    where 1=1
    <if test="name != null">
        and name like CONCAT('%',#{name},'%')
    </if>
    <if test="age != null">
        and age = #{age}
    </if>
</select>
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public class TestMain {
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        try (SqlSession session = sqlSessionFactory.openSession()) {
            // 通过sesson获取Mapper 这个Mapper会编程Mybatis的代理Mapper
            TestMapper mapper = session.getMapper(TestMapper.class);
            List<TestEntity> list = mapper.listByNameAndAge("小强", 19);
            System.out.println(list);
        }
    }
}

2.3.4 多个参数之Map

用Map跟用实体类差不多 就key值当做是实体类的字段名称就可以

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// 多参数Map 方式传递
List<TestEntity> listByNameAndAgeMap(Map<String, Object> param);
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<!--param多参数map使用-->
<select id="listByNameAndAgeMap" resultType="testentity">
    select * from test
    where 1=1
    <if test="name != null">
        and name like CONCAT('%',#{name},'%')
    </if>
    <if test="age != null">
        and age = #{age}
    </if>
</select>
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public class TestMain {
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        try (SqlSession session = sqlSessionFactory.openSession()) {
            // 通过sesson获取Mapper 这个Mapper会编程Mybatis的代理Mapper
            TestMapper mapper = session.getMapper(TestMapper.class);
            Map<String,Object> param = new HashMap<>();
            param.put("name", "小强");
            param.put("age", 19);
            List<TestEntity> list = mapper.listByNameAndAgeMap(param);
            System.out.println(list);
        }
    }
}

2.3.5 多个参数之默认

默认有两套参数：

arg0、arg1、arg2、argxxx ; arg从0开始按照方法参数顺序

param1、param2、param3、paramxxx ; param从1开始按照方法参数顺序

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// 什么都不用
List<TestEntity> listByNameAndAgeNone(String name, int age);
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<!--用默认顺序-->
<select id="listByNameAndAgeNone" resultType="testentity">
    select * from test
    where 1=1
    <if test="arg0 != null">
        and name like CONCAT('%',#{arg0},'%')
    </if>
    <if test="arg1 != null">
        and age = #{arg1}
    </if>
</select>
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<!--用默认顺序-->
<select id="listByNameAndAgeNone" resultType="testentity">
    select * from test
    where 1=1
    <if test="param1 != null">
        and name like CONCAT('%',#{param1},'%')
    </if>
    <if test="param2 != null">
        and age = #{param2}
    </if>
</select>
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public class TestMain {
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        try (SqlSession session = sqlSessionFactory.openSession()) {
            // 通过sesson获取Mapper 这个Mapper会编程Mybatis的代理Mapper
            TestMapper mapper = session.getMapper(TestMapper.class);
            List<TestEntity> list = mapper.listByNameAndAgeNone("小月", 20);
            System.out.println(list);
        }
    }
}

2.3.6 数组参数之基础值&实体类

注意传递数组的话，默认参数名称为arry

1. 根据多个年龄查询数据：
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// 根据年龄集合查询
List<TestEntity> listByAges(int[] ages);
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<select id="listByAges" resultType="testentity">
    select * from test
    where 1=1
    <if test="array != null and array.length >0">
        and age in
        <foreach collection="array" item="age" open="(" separator="," close=")">
        #{age}
</foreach>
    </if>
        </select>
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public class TestMain {
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        try (SqlSession session = sqlSessionFactory.openSession()) {
            // 通过sesson获取Mapper 这个Mapper会编程Mybatis的代理Mapper
            TestMapper mapper = session.getMapper(TestMapper.class);
            int[] ages = new int[]{19,20};
            List<TestEntity> list = mapper.listByAges(ages);
            System.out.println(list);
        }
    }
}
2. 根据名称和年龄多条件查询

例如：名称是小强并且年龄是19 或者名称是小月月年龄是20 的数据

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// 根据多组参数查询
List<TestEntity> listByNameAndAges(TestEntity[] params);
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<select id="listByNameAndAges" resultType="testentity">
    select * from test
    where 1=1
    <if test="array != null and array.length >0">
        and (
        <foreach collection="array" item="item"  separator="or" >
        (name = #{item.name} and age = #{item.age})
        </foreach>
    )
        </if>
</select>
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public class TestMain {
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        try (SqlSession session = sqlSessionFactory.openSession()) {
            // 通过sesson获取Mapper 这个Mapper会编程Mybatis的代理Mapper
            TestMapper mapper = session.getMapper(TestMapper.class);
            TestEntity[] params = new TestEntity[2];
            TestEntity testEntity01 = new TestEntity();
            testEntity01.setName("小强");
            testEntity01.setAge(19);
            TestEntity testEntity02 = new TestEntity();
            testEntity02.setName("小月月");
            testEntity02.setAge(20);
            params[0] =  testEntity01;
            params[1] =  testEntity02;
            List<TestEntity> list = mapper.listByNameAndAges(params);
            System.out.println(list);
        }
    }
}

最后输出的sql格式是这样的：

select* from test where 1=1 and (
(name = '小强' and age = 19) or
(name = '小月月' and age = 20)
)

2.3.7 集合参数之基础值&实体类

集合与数组差不多，但还是有点儿差别

不同点1： 集合如果不指定参数名称的话默认使用：collection或者list 不是array

不同点2：集合判断大小是这样的 用的size() 不是length

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<if test="list != null and list.size() >0"></if>

2.4 四大标签的说明

select是Mybatis使用最多的标签之一，他与insert update delete不同，他不对数据库值做改变，只是查

insert、 update、 delete 会对数据库的值做变更，这三个标签可以混用，也就是说他们功能一样，出三个的意义就是为了业务上可以区分一下是新增、修改还是删除。一般我们也遵循这个使用。

2.5 唠唠

没写动态Sql相关的东西 后边几篇写吧

下期预告：

# {}${} 这哥俩的区别与使用

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原文链接：https://blog.csdn.net/qq_36291682/article/details/119974538

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