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这篇文章主要介绍了Mybatis中实体类别名、多参数、动态SQL的示例分析，具有一定借鉴价值，感兴趣的朋友可以参考下，希望大家阅读完这篇文章之后大有收获，下面让小编带着大家一起了解一下。
开始讲实体类别名、多参数、动态SQL等
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');
package entity;
import java.math.BigDecimal;
/**
* @author 发现更多精彩 关注公众号：木子的昼夜编程
* 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
}mybatis-config.xml
<?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>
<!--根据主键查询-->
<select id="get" resultType="testEntity">
select * from test where id = #{id}
</select>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);
}
}
}扫描包路径 mybatis-config.xml
<?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：
@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“
| 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 |
<!--增加-->
<insert id="save" useGeneratedKeys="true" keyProperty="id">
INSERT INTO `test`( `name`, `salary`) VALUE (#{name}, #{salary});
</insert>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：
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
<!--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>// 根据主键查询 TestEntity get(Long id);
<!--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
// 新增 void save(TestEntity testEntity);
<!--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
// 根据名称模糊查询
List<TestEntity> listByNameAndAge(@Param("name") String name,@Param("age") Integer age);<!--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>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);
}
}
}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
// 多参数Map 方式传递 List<TestEntity> listByNameAndAgeMap(Map<String, Object> param);
<!--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>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);
}
}
}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
// 什么都不用 List<TestEntity> listByNameAndAgeNone(String name, int age);
<!--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><!--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>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);
}
}
}注意传递数组的话，默认参数名称为arry
// 根据年龄集合查询 List<TestEntity> listByAges(int[] ages);
<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>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);
}
}
}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
// 根据多组参数查询 List<TestEntity> listByNameAndAges(TestEntity[] params);
<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>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)
)
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
<if test="list != null and list.size() >0"></if>
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。
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