1.if语句

如果empno不为空，则在WHERE参数后加上AND empno = #{empno},这里有1=1所以即使empno为null，WHERE后面也不会报错。

映射文件

         SELECT * FROM emp WHERE 1=1                    AND empno = #{empno}               

EmpMapper接口

public Emp getEmpById2(@Param("empno")Integer empno) throws IOException;

有时候我们并不想应用所有的条件，而只是想从多个选项中选择一个。而使用if标签时，只要test中的表达式为 true，就会执行 if 标签中的条件。MyBatis 提供了 choose 元素。if标签是与(and)的关系，而 choose 是或(or)的关系。

2.where语句和Choose(when,otherwise)

1.Where后面empno和ename为null，那where就不会出现在sql语句中。

1. choose标签是按顺序判断其内部when标签中的test条件出否成立，如果有一个成立，则 choose 结束。当 choose 中所有 when 的条件都不满则时，则执行 otherwise 中的sql。类似于Java 的 switch 语句，choose 为 switch，when 为 case，otherwise 则为 default。

映射文件

        SELECT * FROM EMP                                                         AND empno like #{empno}                                                    AND ename like #{ename}                                                    AND  job = "zz"                                        

EmpMapper接口

public Emp getEmpById3(Emp emp) throws IOException;

3.set语句

set主要也是用来解决更新问题的。

映射文件

    
             UPDATE emp        
                 
      
        ename=#{ename},
                  
      
        job=#{job},
              
             
                 
      
                       empno=#{empno};            
              
         
    

EmpMapper接口

public Integer updateEmprById2(Emp emp) throws IOException;

4.trim

 trim标记是一个格式化的标记，可以完成set或者是where标记的功能。

相关属性：

Prefix：前缀。

prefixOverrides：去掉第一个指定内容。

suffix：后缀。

suffixoverride：去掉最后一个指定内容。

映射文件

                SELECT * FROM emp        
                                         and empno = #{empno}                                        AND ename = #{ename}                        

映射文件

        
    
             update emp        
                 
      
                       ename = #{ename},            
                  
      
                       job = #{job}            
              
             
                 
      
                       and empno = #{empno}            
              
         
    

EmpMapper接口

public Emp getEmpById4(Emp emp) throws IOException;    public Integer updateEmprById3(Emp emp) throws IOException;

5.foreach语句

foreach用来遍历，遍历的对象可以是数组，也可以是集合。

相关属性：

Collection：collection属性的值有三个分别是list、array、map三种。

Open：前缀。

Close：后缀。

Separator：分隔符，表示迭代时每个元素之间以什么分隔。

Item：表示在迭代过程中每一个元素的别名。

Index：用一个变量名表示当前循环的索引位置。

映射文件

    
             insert into emp(ename,job)values        
     
                  (#{emp.ename},#{emp.job})        
         
    

EmpMapper接口

public int addEmp6(@Param("emps")List
    
      emps);
    

6.SQL块

映射文件

        
    
             empno,ename,job    
            
                select                  from emp     

EmpMapper接口

public List
    
      selEmp1() throws IOException;
    

7.bind

映射文件

        
                     select * from emp where empno=${empno}    

EmpMapper接口

public Emp getEmpById6()throws IOException;

全部代码：

EmpMapper接口

package com.zsl.dao;import java.io.IOException;import java.util.List;import org.apache.ibatis.annotations.Param;import com.zsl.pojo.Emp;public interface EmpMapper {    public Integer addEmp(Emp emp) throws IOException;        public Integer deleteEmpById(Integer empno) throws IOException;    public Integer updateEmprById(Emp emp) throws IOException;        public Emp getEmpById(@Param("empno")Integer empno) throws IOException;        public Integer addEmp1(String ename,String job) throws IOException;    public Integer addEmp2(String ename,String job) throws IOException;        public Integer addEmp3(@Param("ename")String ename,@Param("job")String job) throws IOException;        public Integer addEmp4(@Param("ename")String ename,@Param("job")String job) throws IOException;        public List
    
      selEmp() throws IOException;        public Emp getEmpById2(@Param("empno")Integer empno) throws IOException;        public Emp getEmpById3(Emp emp) throws IOException;    public Integer updateEmprById2(Emp emp) throws IOException;    public Emp getEmpById4(Emp emp) throws IOException;    public Integer updateEmprById3(Emp emp) throws IOException;    // 如果不指定@Param 默认是array    public List
     
       getEmpById5(@Param("empnos")List
      
        empno);    public int addEmp6(@Param("emps")List
       
         emps);    public List
        
          selEmp1() throws IOException;    public Emp getEmpById6()throws IOException;}
        
       
      
     
    

EmpMapper.XML映射文件

    
        
         
     
               delete from emp where empno=#{empno}        
         
     
               update emp set name = #{ename} where empno=#{empno}        
             
              select * from emp where empno=${empno}               
     
              insert into emp(ename,job)values(#{arg0},#{arg1})    
             
     
              insert into emp(ename,job)values(#{param1},#{param2})    
             
     
              insert into emp(ename,job)values(${ename},${job})    
             
     
              insert into emp(ename,job)values(#{ename},#{job})    
             
              select empno empno,ename ename,job job,mgr mgrA from emp            
             
              
              
              
           
              
              select * from emp           
         
     
              insert into emp(ename,job)values(#{ename},#{job})    
              
             
      
                   select            LAST_INSERT_ID()        
              insert into emp(ename,job)values(#{ename},#{job})    
         
              SELECT * FROM emp WHERE 1=1                    AND empno = #{empno}                   
             SELECT * FROM EMP                                                         AND empno like #{empno}                                                    AND ename like #{ename}                                                    AND  job = "zz"                                            
     
              UPDATE emp        
                  
       
         ename=#{ename},
                   
       
         job=#{job},
               
              
                  
       
                        empno=#{empno};            
               
          
             
         
             SELECT * FROM emp        
                                          and empno = #{empno}                                        AND ename = #{ename}                        
         
     
              update emp        
                  
       
                        ename = #{ename},            
                   
       
                        job = #{job}            
               
              
                  
       
                        and empno = #{empno}            
               
          
         
             select * from emp where empno in                    #{empno}                
     
              insert into emp(ename,job)values        
      
                   (#{emp.ename},#{emp.job})        
          
             
         
     
              empno,ename,job    
             
         
             select                  from emp         
             
                      select * from emp where empno=${empno}    
    

全局配置文件

mybatis-cfg.xml

Pojo

package com.zsl.pojo;import java.util.List;public class Emp {    private Integer empno;    private String ename;    private String job;    private Integer mgrA;//这里与数据库字段名称不同，数据库字段为mgr    public Integer getEmpno() {        return empno;    }    public void setEmpno(Integer empno) {        this.empno = empno;    }    public String getEname() {        return ename;    }    public void setEname(String ename) {        this.ename = ename;    }    public String getJob() {        return job;    }    public void setJob(String job) {        this.job = job;    }    public Emp() {        super();        // TODO Auto-generated constructor stub    }    public Integer getMgrA() {        return mgrA;    }    public void setMgrA(Integer mgrA) {        this.mgrA = mgrA;    }    public Emp(Integer empno, String ename, String job, Integer mgrA) {        super();        this.empno = empno;        this.ename = ename;        this.job = job;//      this.mgrA = mgrA;    }    @Override    public String toString() {        return "Emp [empno=" + empno + ", ename=" + ename + ", job=" + job  + "]";        //+ ", mgrA=" + mgrA    }}

DBUtils

package com.zsl.utils;import java.io.IOException;import java.io.InputStream;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;public class DbUtils {    public static SqlSession getSession() throws IOException {        // TODO Auto-generated method stub        // 1.通过Resources对象加载配置文件        InputStream inputStream = Resources.getResourceAsStream("mybatis-cfg.xml");        // 2.获取SqlSessionFactory对象        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);        // 3.通过SqlSessionFactory对象获取SQLSession对象        SqlSession session = factory.openSession();        return session;    }        public static void commit(SqlSession session) {        // TODO Auto-generated method stub        session.commit();    }        public static void close(SqlSession session) {        // TODO Auto-generated method stub        session.close();    }}

测试类Test

package com.zsl.test;import java.io.IOException;import java.io.InputStream;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.ArrayList;import java.util.List;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import com.zsl.dao.EmpMapper;import com.zsl.pojo.Emp;import com.zsl.utils.DbUtils;public class Test {    public static void main(String[] args) throws IOException {        Test test = new Test();        System.out.println(test.addUser3());    }    public Integer addUser1() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Integer integer = mapper.addEmp1("zsladd1", "程序员1");        session.commit();        session.close();        return integer;    }    public Integer addUser2() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Integer integer = mapper.addEmp2("zsladd2", "程序员2");        session.commit();        session.close();        return integer;    }    public Integer addUser3() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Integer integer = mapper.addEmp3("zsladd3", "程序员3");        session.commit();        session.close();        return integer;    }    public Integer addUser4() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Integer integer = mapper.addEmp4("zsladd4", "程序员4");        session.commit();        session.close();        return integer;    }    public Emp getEmpById() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Emp emp = mapper.getEmpById(7902);        session.close();        return emp;    }    public List
    
      selEmp() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        List
     
       list = mapper.selEmp();        return list;    }    public Integer addUser() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Emp emp = new Emp();        emp.setEname("zsl00");        emp.setJob("程序员00");        Integer integer = mapper.addEmp(emp);        System.out.println("该条记录主键：" + emp.getEmpno());        session.commit();        session.close();        return integer;    }    public Emp getEmpById2() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Emp emp = mapper.getEmpById2(7900);        session.close();        return emp;    }        public Emp getEmpById3() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Emp emp2 = new Emp();        emp2.setEname("JAMES");        Emp emp = mapper.getEmpById3(emp2);        return emp;    }    public Integer updateEmprById2() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Emp emp = new Emp();        emp.setEmpno(7941);        emp.setEname("zsl55");        emp.setJob("程序员55");        Integer integer = mapper.updateEmprById2(emp);        session.commit();        session.close();        return integer;    }        public Integer updateEmprById3() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Emp emp = new Emp();        emp.setEmpno(7941);        emp.setEname("zsl77");        emp.setJob("程序员77");        Integer integer = mapper.updateEmprById2(emp);        session.commit();        session.close();        return integer;    }        public Emp getEmpById4() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        Emp emp2 = new Emp();        emp2.setEname("JAMES");        Emp emp = mapper.getEmpById3(emp2);        session.close();        return emp;    }        public List
      
        getEmpById5() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        List
       
         list = new ArrayList<>();        list.add(7969);        list.add(7970);        list.add(7971);        List
        
          empList = mapper.getEmpById5(list);        session.close();        return empList;    }        public Integer addEmp6() throws IOException {        // TODO Auto-generated method stub        SqlSession session = DbUtils.getSession();        EmpMapper mapper = session.getMapper(EmpMapper.class);        List
         
           emps = new ArrayList<>(); Emp emp = new Emp(); emp.setEname("zsl88"); emp.setJob("程序员88"); emps.add(emp); Emp empA = new Emp(); empA.setEname("zsl99"); empA.setJob("程序员99"); emps.add(empA); int addEmp6 = mapper.addEmp6(emps); session.commit(); session.close(); return addEmp6; } public List
          
            selEmp1() throws IOException { // TODO Auto-generated method stub SqlSession session = DbUtils.getSession(); EmpMapper mapper = session.getMapper(EmpMapper.class); List
           
             list = mapper.selEmp1(); session.close(); return list; } public Emp getEmpById6() throws IOException { // TODO Auto-generated method stub SqlSession session = DbUtils.getSession(); EmpMapper mapper = session.getMapper(EmpMapper.class); Emp emp = mapper.getEmpById6(); session.close(); return emp; }}