mybatis注解实现动态sql

  在整合ssm的时候，遇到一个多表联合(多表，多条件组合，分页)查询的问题，需要自定义mapper.xml,  但本人又比较反感写xml文件，总感觉配置文件没有注解来的简洁，于是用到了 “注解实现动态sql” ,所以总结一下供日后回顾。 //简单的查询

  第一步：定义一个实体类Student用作映射。

public class Student {
    private Integer id;
    private String username;
    private String password;
    private String addr;

	//Generate Getter and Setter 此处省略
}

  第二步：定义mapper， 在对应接口的类上和方法加对应的注解 type指定生成sql的类，method指定用哪个方法。

/**
 * Created with IDEA
 * author:bigStone
 * Date:2019/5/2
 **/
@MapperScan       //把Mapper交给spring管理
public interface StudentMapper {

    @SelectProvider(type = StudentSqlProvider.class, method="select")
    List<Student> findAll(Student student) throws Exception;
    
    @InsertProvider(type = StudentSqlProvider.class , method = "insertStudent" )
    void insert(Student student) throws Exception;
    
    @DeleteProvider(type = StudentSqlProvider.class, method = "delete")
    void delete(Student student) throws Exception;

    @UpdateProvider(type = StudentSqlProvider.class, method = "update")
    void update(Student student) throws Exception;
    
}

  第三步：定义生成sql的类StudentSqlProvider，并定义需要的方法

import org.apache.ibatis.jdbc.SQL;
import yycg.base.domain.test.Student;

/**
 * Created with IDEA
 * author:bigStone
 * Date:2019/5/2
 **/
public class StudentSqlProvider {

    //插入
    public String insertStudent(Student student) {
        SQL sql = new SQL();
        sql.INSERT_INTO("student");
        if (student.getId() != null) {
            sql.VALUES("id", "#{id}");
        }
        if (student.getUsername() != null) {
            sql.VALUES("username", "#{username}");
        }
        if (student.getPassword() != null) {
            sql.VALUES("password", "#{password}");
        }
        if (student.getAddr() != null) {
            sql.VALUES("addr", "#{addr}");
        }
        return sql.toString();
    }

    //查询
    public String select(Student student) {
        return new SQL() {
         
  {
            SELECT("id, username, password, addr");
            FROM("student");
            if (student != null) {
                if (student.getId() != null) {
                    WHERE("id = #{id}");
                }
                if (student.getUsername() != null) {
                    WHERE("username like % #{username} %");
                }
                if (student.getPassword() != null) {
                    WHERE("password = #{password}");
                }
                if (student.getAddr() != null) {
                    WHERE("addr like % #{addr} % ");
                }
            }
        }}.toString();
    }

    //删除
    public String delete(Student student) {
        return new SQL() {
         
  {
            DELETE_FROM("student");
            if (student.getId() != null) {
                WHERE("id = #{id}");
            }
        }}.toString();
    }

    //更新
    public String update(Student student) {
        return new SQL() {
         
  {
            UPDATE("student");
            if (student.getUsername() != null) {
                SET("username = #{username}");
            }
            if (student.getPassword() != null) {
                SET("password = #{password}");
            }
            if (student.getAddr() != null) {
                SET("addr = #{addr}");
            }
            WHERE("id = #{id}");
        }}.toString();
    }
}

然后调用mapper接口的方法即可.