MyBatis的数据库操作。
在初识MyBatis这篇文章中已经讲述了关于MyBatis的搭建、简单的增删改查及获取参数值等内容,这篇文章继续讲诉MyBatis的数据库操作。
{password=123456, sex=男, id=1, age=23, username=admin}
/**
* 根据用户id查询用户信息
* @param id
* @return
*/
User getUserById(@Param("id") int id);
<select id="getUserById" resultType="User">
select * from t_user where id = #{id}
select>
/**
* 查询所有用户信息
* @return
*/
List<User> getUserList();
<select id="getUserList" resultType="User">
select * from t_user
select>
/**
* 查询用户的总记录数
* @return
* 在MyBatis中,对于Java中常用的类型都设置了类型别名
* 例如:java.lang.Integer-->int|integer
* 例如:int-->_int|_integer
* 例如:Map-->map,List-->list
*/
int getCount();
<select id="getCount" resultType="_integer">
select count(id) from t_user
select>
/**
* 根据用户id查询用户信息为map集合
* @param id
* @return
*/
Map<String, Object> getUserToMap(@Param("id") int id);
<select id="getUserToMap" resultType="map">
select * from t_user where id = #{id}
select>
/**
* 查询所有用户信息为map集合
* @return
* 将表中的数据以map集合的方式查询,一条数据对应一个map;若有多条数据,就会产生多个map集合,此时可以将这些map放在一个list集合中获取
*/
List<Map<String, Object>> getAllUserToMap1();
<select id="getAllUserToMap" resultType="map">
select * from t_user
select>
/**
* 查询所有用户信息为map集合
* @return
* 将表中的数据以map集合的方式查询,一条数据对应一个map;若有多条数据,就会产生多个map集合,并且最终要以一个map的方式返回数据,此时需要通过@MapKey注解设置map集合的键,值是每条数据所对应的map集合
*/
@MapKey("id")
Map<String, Object> getAllUserToMap2();
<select id="getAllUserToMap" resultType="map">
select * from t_user
select>
package com.dragon.mybatis.test;
import com.dragon.mybatis.mapper.SelectMapper;
import com.dragon.mybatis.pojo.User;
import com.dragon.mybatis.utils.SqlSessionUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class SelectMapperTest {
@Test
public void testGetUserById(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getUserById(3));
}
@Test
public void testGetAllUser(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
List<User> users=mapper.getAllUser();
users.forEach(user -> System.out.println(user));
}
@Test
public void testGetCount(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getCount());
}
@Test
public void testGetUserToMap(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getUserToMap(3));
}
@Test
public void testAllUserToMap1(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getAllUserToMap1());
}
@Test
public void testAllUserToMap2(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getAllUserToMap2());
}
}
/**
* 根据用户名进行模糊查询
* @param username
* @return java.util.List
* @date 2023/8/26 21:56
*/
List<User> getUserByLike(@Param("username") String username);
<select id="getUserByLike" resultType="User">
select * from t_user where username like "%"#{username}"%"
select>
select * from t_user where username like "%"#{username}"%"
是最常用的delete from t_user where id in ('1,2,3')
,这样是将1,2,3
看做是一个整体,只有id为1,2,3
的数据会被删除。正确的语句应该是delete from t_user where id in (1,2,3)
,或者delete from t_user where id in ('1','2','3')
/**
* 根据id批量删除
* @param ids
* @return int
* @date 2023/8/26 22:06
*/
int deleteMore(@Param("ids") String ids);
<delete id="deleteMore">
delete from t_user where id in (${ids})
delete>
//测试类
@Test
public void deleteMore() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
int result = mapper.deleteMore("1,2,3,8");
System.out.println(result);
}
/**
* 查询指定表中的数据
* @param tableName
* @return java.util.List
* @date 2023/8/27 14:41
*/
List<User> getUserByTable(@Param("tableName") String tableName);
<select id="getUserByTable" resultType="User">
select * from ${tableName}
select>
/**
* 添加用户信息
* @param user
* @date 2023/8/27 15:04
*/
void insertUser(User user);
<insert id="insertUser" useGeneratedKeys="true" keyProperty="id">
insert into t_user values (null,#{username},#{password},#{age},#{sex},#{email})
insert>
package com.dragon.mybatis.test;
import com.dragon.mybatis.mapper.SQLMapper;
import com.dragon.mybatis.pojo.User;
import com.dragon.mybatis.utils.SqlSessionUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class SQLMapperTest {
@Test
public void testUserByLike(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
List<User> list = mapper.getUserByLike("a");
System.out.println(list);
}
@Test
public void testDeleteMore(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
int result = mapper.deleteMore("1,2,3");
System.out.println(result);
}
@Test
public void testGetUserByTable(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
List<User> list= mapper.getUserByTable("t_user");
System.out.println(list);
}
@Test
public void insertUser() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
User user = new User(null, "ton", "123", 23, "男", "[email protected]");
mapper.insertUser(user);
System.out.println(user);
//输出:user{id=10, username='ton', password='123', age=23, sex='男', email='[email protected]'},自增主键存放到了user的id属性中
}
}
<resultMap id="empResultMap" type="Emp">
<id property="eid" column="eid">id>
<result property="empName" column="emp_name">result>
<result property="age" column="age">result>
<result property="sex" column="sex">result>
<result property="email" column="email">result>
resultMap>
<select id="getAllEmp" resultMap="empResultMap">
select * from t_emp
select>
<select id="getAllEmp" resultType="Emp">
select eid,emp_name empName,age,sex,email from t_emp
select>
setting
标签中,设置一个全局配置信息mapUnderscoreToCamelCase,可以在查询表中数据时,自动将_类型的字段名转换为驼峰,例如:字段名user_name,设置了mapUnderscoreToCamelCase,此时字段名就会转换为userName。 <settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
settings>
查询员工信息以及员工所对应的部门信息
public class Emp {
private Integer eid;
private String empName;
private Integer age;
private String sex;
private String email;
private Dept dept;
//...构造器、get、set方法等
}
<resultMap id="empAndDeptResultMapOne" type="Emp">
<id property="eid" column="eid">id>
<result property="empName" column="emp_name">result>
<result property="age" column="age">result>
<result property="sex" column="sex">result>
<result property="email" column="email">result>
<result property="dept.did" column="did">result>
<result property="dept.deptName" column="dept_name">result>
resultMap>
<select id="getEmpAndDept" resultMap="empAndDeptResultMapOne">
select * from t_emp left join t_dept on t_emp.eid = t_dept.did where t_emp.eid = #{eid}
select>
<resultMap id="empAndDeptResultMapTwo" type="Emp">
<id property="eid" column="eid">id>
<result property="empName" column="emp_name">result>
<result property="age" column="age">result>
<result property="sex" column="sex">result>
<result property="email" column="email">result>
<association property="dept" javaType="Dept">
<id property="did" column="did">id>
<result property="deptName" column="dept_name">result>
association>
resultMap>
<select id="getEmpAndDept" resultMap="empAndDeptResultMapTwo">
select * from t_emp left join t_dept on t_emp.eid = t_dept.did where t_emp.eid = #{eid}
select>
//EmpMapper里的方法
/**
* 通过分步查询,员工及所对应的部门信息
* 分步查询第一步:查询员工信息
* @param
* @return com.dragon.mybatis.pojo.Emp
* @date 2022/2/27 20:17
*/
Emp getEmpAndDeptByStepOne(@Param("eid") Integer eid);
<resultMap id="empAndDeptByStepResultMap" type="Emp">
<id property="eid" column="eid">id>
<result property="empName" column="emp_name">result>
<result property="age" column="age">result>
<result property="sex" column="sex">result>
<result property="email" column="email">result>
<association property="dept"
select="com.dragon.mybatis.mapper.DeptMapper.getEmpAndDeptByStepTwo"
column="did">association>
resultMap>
<select id="getEmpAndDeptByStepOne" resultMap="empAndDeptByStepResultMap">
select * from t_emp where eid = #{eid}
select>
//DeptMapper里的方法
/**
* 通过分步查询,员工及所对应的部门信息
* 分步查询第二步:通过did查询员工对应的部门信息
* @param
* @return com.dragon.mybatis.pojo.Emp
* @date 2022/2/27 20:23
*/
Dept getEmpAndDeptByStepTwo(@Param("did") Integer did);
<resultMap id="EmpAndDeptByStepTwoResultMap" type="Dept">
<id property="did" column="did">id>
<result property="deptName" column="dept_name">result>
resultMap>
<select id="getEmpAndDeptByStepTwo" resultMap="EmpAndDeptByStepTwoResultMap">
select * from t_dept where did = #{did}
select>
public class Dept {
private Integer did;
private String deptName;
private List<Emp> emps;
//...构造器、get、set方法等
}
<resultMap id="DeptAndEmpResultMap" type="Dept">
<id property="did" column="did">id>
<result property="deptName" column="dept_name">result>
<collection property="emps" ofType="Emp">
<id property="eid" column="eid">id>
<result property="empName" column="emp_name">result>
<result property="age" column="age">result>
<result property="sex" column="sex">result>
<result property="email" column="email">result>
collection>
resultMap>
<select id="getDeptAndEmp" resultMap="DeptAndEmpResultMap">
select * from t_dept left join t_emp on t_dept.did = t_emp.did where t_dept.did = #{did}
select>
//DeptMapper
/**
* 通过分步查询,查询部门及对应的所有员工信息
* 分步查询第一步:查询部门信息
* @param did
* @return com.dragon.mybatis.pojo.Dept
* @date 2023/8/27 22:04
*/
Dept getDeptAndEmpByStepOne(@Param("did") Integer did);
<resultMap id="DeptAndEmpByStepOneResultMap" type="Dept">
<id property="did" column="did">id>
<result property="deptName" column="dept_name">result>
<collection property="emps"
select="com.atguigu.mybatis.mapper.EmpMapper.getDeptAndEmpByStepTwo"
column="did">collection>
resultMap>
<select id="getDeptAndEmpByStepOne" resultMap="DeptAndEmpByStepOneResultMap">
select * from t_dept where did = #{did}
select>
//EmpMapper
/**
* 通过分步查询,查询部门及对应的所有员工信息
* 分步查询第二步:根据部门id查询部门中的所有员工
* @param did
* @return java.util.List
* @date 2023/8/27 22:10
*/
List<Emp> getDeptAndEmpByStepTwo(@Param("did") Integer did);
<select id="getDeptAndEmpByStepTwo" resultType="Emp">
select * from t_emp where did = #{did}
select>
<settings>
<setting name="lazyLoadingEnabled" value="true"/>
settings>
@Test
public void getEmpAndDeptByStepOne() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Emp emp = mapper.getEmpAndDeptByStepOne(1);
System.out.println(emp.getEmpName());
}
@Test
public void getEmpAndDeptByStepOne() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Emp emp = mapper.getEmpAndDeptByStepOne(1);
System.out.println(emp.getEmpName());
System.out.println("----------------");
System.out.println(emp.getDept());
}
fetchType:当开启了全局的延迟加载之后,可以通过该属性手动控制延迟加载的效果,fetchType=“lazy(延迟加载)|eager(立即加载)”
<resultMap id="empAndDeptByStepResultMap" type="Emp">
<id property="eid" column="eid">id>
<result property="empName" column="emp_name">result>
<result property="age" column="age">result>
<result property="sex" column="sex">result>
<result property="email" column="email">result>
<association property="dept"
select="com.atguigu.mybatis.mapper.DeptMapper.getEmpAndDeptByStepTwo"
column="did"
fetchType="lazy">association>
resultMap>
import com.dragon.mybatis.mapper.DeptMapper;
import com.dragon.mybatis.mapper.EmpMapper;
import com.dragon.mybatis.pojo.Dept;
import com.dragon.mybatis.pojo.Emp;
import com.dragon.mybatis.utils.SqlSessionUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class ResultMapTest {
@Test
public void testGetAllEmp(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
List<Emp> list = mapper.getAllEmp();
System.out.println(list);
}
@Test
public void testGetAndDept(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Emp emp = mapper.getEmpAndDept(1);
System.out.println(emp);
}
@Test
public void testGetAndDeptByStep(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Emp emp = mapper.getEmpAndDeptByStepOne(1);
System.out.println(emp);
}
@Test
public void testGetDeptAndEmp(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DeptMapper mapper = sqlSession.getMapper(DeptMapper.class);
Dept dept = mapper.getDeptAndEmp(1);
System.out.println(dept);
}
@Test
public void testGetDeptAndEmpByStep(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DeptMapper mapper = sqlSession.getMapper(DeptMapper.class);
Dept dept = mapper.getDeptAndEmpByStepOne(1);
System.out.println(dept);
}
}
1=1
1=1
可以用来拼接and
语句,例如:当empName为null时
select * from t_emp where and age = ? and sex = ? and email = ?
,此时where
会与and
连用,SQL语句会报错select * from t_emp where 1= 1 and age = ? and sex = ? and email = ?
,此时不报错
<select id="getEmpByCondition1" resultType="Emp">
select * from t_emp where 1=1
<if test="empName != null and empName !=''">
and emp_name = #{empName}
if>
<if test="age != null and age !=''">
and age = #{age}
if>
<if test="sex != null and sex !=''">
and sex = #{sex}
if>
<if test="email != null and email !=''">
and email = #{email}
if>
select>
<select id="getEmpByCondition2" resultType="Emp">
select * from t_emp
<where>
<if test="empName != null and empName !=''">
emp_name = #{empName}
if>
<if test="age != null and age !=''">
and age = #{age}
if>
<if test="sex != null and sex !=''">
and sex = #{sex}
if>
<if test="email != null and email !=''">
and email = #{email}
if>
where>
select>
<if test="empName != null and empName !=''">
emp_name = #{empName} and
if>
<if test="age != null and age !=''">
age = #{age}
if>
select * from t_emp
<select id="getEmpByCondition3" resultType="Emp">
select * from t_emp
<trim prefix="where" suffixOverrides="and|or">
<if test="empName != null and empName !=''">
emp_name = #{empName} and
if>
<if test="age != null and age !=''">
age = #{age} and
if>
<if test="sex != null and sex !=''">
sex = #{sex} or
if>
<if test="email != null and email !=''">
email = #{email}
if>
trim>
select>
choose、when、otherwise
相当于if...else if..else
<select id="getEmpByChoose" resultType="Emp">
select * from t_emp
<where>
<choose>
<when test="empName != null and empName != ''">
emp_name = #{empName}
when>
<when test="age != null and age != ''">
age = #{age}
when>
<when test="sex != null and sex != ''">
sex = #{sex}
when>
<when test="email != null and email != ''">
email = #{email}
when>
<otherwise>
did = 1
otherwise>
choose>
where>
select>
@Test
public void getEmpByChoose() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
List<Emp> emps = mapper.getEmpByChoose(new Emp(null, "张三", 23, "男", "[email protected]", null));
System.out.println(emps);
}
if a else if b else if c else d
,只会执行其中一个属性:
,
批量删除
<delete id="deleteMoreByArray">
delete from t_emp where eid in
<foreach collection="eids" item="eid" separator="," open="(" close=")">
#{eid}
foreach>
delete>
@Test
public void deleteMoreByArray() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
int result = mapper.deleteMoreByArray(new Integer[]{6, 7, 8, 9});
System.out.println(result);
}
批量添加
<insert id="insertMoreByList">
insert into t_emp values
<foreach collection="emps" item="emp" separator=",">
(null,#{emp.empName},#{emp.age},#{emp.sex},#{emp.email},null)
foreach>
insert>
@Test
public void insertMoreByList() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
Emp emp1 = new Emp(null,"a",1,"男","[email protected]",null);
Emp emp2 = new Emp(null,"b",1,"男","[email protected]",null);
Emp emp3 = new Emp(null,"c",1,"男","[email protected]",null);
List<Emp> emps = Arrays.asList(emp1, emp2, emp3);
int result = mapper.insertMoreByList(emps);
System.out.println(result);
}
标签<sql id="empColumns">eid,emp_name,age,sex,emailsql>
标签
<select id="getEmpByCondition" resultType="Emp">
select <include refid="empColumns">include> from t_emp
select>
import com.dragon.mybatis.mapper.DynamicSQLMapper;
import com.dragon.mybatis.pojo.Emp;
import com.dragon.mybatis.utils.SqlSessionUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.Arrays;
import java.util.List;
public class DynamicSQLMapperTest {
@Test
public void testGetEmpByCondition1(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
List<Emp> list = mapper.getEmpByCondition1(new Emp(null,"张三",23,"男","[email protected]",null));
System.out.println(list);
}
@Test
public void testGetEmpByCondition2(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
List<Emp> list = mapper.getEmpByCondition2(new Emp(null,"",23,"男","[email protected]",null));
System.out.println(list);
}
@Test
public void testGetEmpByCondition3(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
List<Emp> list = mapper.getEmpByCondition3(new Emp(null,"",null,"","",null));
System.out.println(list);
}
@Test
public void getEmpByChoose() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
List<Emp> emps = mapper.getEmpByChoose(new Emp(null, "张三", 23, "男", "[email protected]", null));
System.out.println(emps);
}
@Test
public void deleteMoreByArray() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
int result = mapper.deleteMoreByArray(new Integer[]{6, 7, 8, 9});
System.out.println(result);
}
@Test
public void insertMoreByList() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
Emp emp1 = new Emp(null,"a",1,"男","[email protected]",null);
Emp emp2 = new Emp(null,"b",1,"男","[email protected]",null);
Emp emp3 = new Emp(null,"c",1,"男","[email protected]",null);
List<Emp> emps = Arrays.asList(emp1, emp2, emp3);
int result = mapper.insertMoreByList(emps);
System.out.println(result);
}
}
以上就是MyBatis的数据库操作。