一. MyBatis 多表操作

  • 创建之后用到的表 
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    create database db4;
    use db4;

    create table card(
                            id int primary key auto_increment,
                            number varchar(20),
                            pid int,

                            constraint cp_fk foreign key (pid) references person(id)

    );
    insert into card values (null,'12345',1);
    insert into card values (null,'23456',2);
    insert into card values (null,'34567',3);
    ==============================================================
    create table person(
                         id int primary key auto_increment,
                         name varchar(20),
                         age int
    );
    insert into person values (null,'张三',23);
    insert into person values (null,'李四',24);
    insert into person values (null,'王五',25);
    ==============================================================
    create table classes(
        id int primary key auto_increment,
        name varchar(20)
    );
    insert into classes values (null,'黑马一班');
    insert into classes values (null,'黑马二班');
    ==============================================================
    create table student(
                            id int primary key auto_increment,
                            name varchar(30),
                            age int,
                            cid int,
                            constraint cs_fk foreign key (cid) references classes(id)
    );
    insert into student values (null,'张三',23,1);
    insert into student values (null,'李四',24,1);
    insert into student values (null,'王五',25,2);
    insert into student values (null,'马六',26,2);
    ==============================================================
    create table course(
                            id int primary key auto_increment,
                            name varchar(30)
    );
    insert into course values (null,'语文');
    insert into course values (null,'数学');
    ==============================================================
    create table stu_cr(
                           id int primary key auto_increment,
                           sid int,
                           cid int,
                           constraint sc_fk1 foreign key (sid) references student(id),
                           constraint sc_fk2 foreign key (cid) references course(id)
    );
    insert into stu_cr values (null,1,1),(null,1,2),(null,2,1),(null,2,2);

获取sqlsession会话对象工具类

  • SqlsessionUtils 
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    public classSessionUtils {
    public staticSqlSession getSqlsession(){
            SqlSession sqlSession =null;
    try{
                InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
                SqlSessionFactory factory =newSqlSessionFactoryBuilder().build(is);
                is.close();
                sqlSession = factory.openSession(true);
            }catch(IOException e) {
                e.printStackTrace();
            }finally{
    returnsqlSession;
            }
        }
    }

1.一对一

1to1.jpg

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create table card(
                        idint primary key auto_increment,
numbervarchar(20),
                        pidint,

constraintcp_fkforeign key(pid)referencesperson(id)

);
insert intocardvalues(null,'12345',1);
insert intocardvalues(null,'23456',2);
insert intocardvalues(null,'34567',3);

create table person(
                     id int primary key auto_increment,
                     name varchar(20),
                     age int
);
insert into person values (null,'张三',23);
insert into person values (null,'李四',24);
insert into person values (null,'王五',25);

pojo类

  • Person 
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    privateInteger id;
    privateString name;
    privateInteger age;
  • Card 
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    privateInteger id;
    privateString number;

    privatePerson p;

interface接口:

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public interface OtoMapper {
//一对一
List<Card> selectAll();
}

mapper映射:

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<mapper namespace="com.itheima.mapper.OtoMapper">

    <resultMap id="OneToOne" type="card">
        <id column="cid" property="id"/>
        <result column="number" property="number"/>

<!--        association：配置被包含对象的映射关系-->
<!--        property：被包含对象变量名-->
<!--        javaType：被包含对象数据类型-->
<association property="p" javaType="person">
            <id column="pid" property="id"/>
            <result column="name" property="name"/>
            <result column="age" property="age"/>
        </association>
    </resultMap>

<!--    List<Card> selectAll();一对一-->
<select id="selectAll" resultMap="OneToOne">
        select c.id cid,number,pid,name,age from card c,person p where c.pid=p.id;
    </select>
</mapper>

Test类：

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//一对一
@Test
public voidselectAll(){
        SqlSession sqlSession = SessionUtils.getSqlsession();

        OtoMapper mapper = sqlSession.getMapper(OtoMapper.class);
        List<Card> cards = mapper.selectAll();

for(Card c : cards) {
            System.out.println(c);
        }

        sqlSession.close();
}

查询结果：
Card{id=1, number=’123456’, p=Person{id=1, name=’张三’, age=23}}
Card{id=2, number=’234567’, p=Person{id=2, name=’李四’, age=24}}
Card{id=3, number=’345678 ‘, p=Person{id=3, name=’王五 ‘, age=25}}

2.一对多

onetomany.jpg

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create table classes(
    id int primary key auto_increment,
    name varchar(20)
);
insert into classes values (null,'黑马一班');
insert into classes values (null,'黑马二班');

create table student(
                        id int primary key auto_increment,
                        name varchar(30),
                        age int,
                        cid int,
                        constraint cs_fk foreign key (cid) references classes(id)
);
insert into student values (null,'张三',23,1);
insert into student values (null,'李四',24,1);
insert into student values (null,'王五',25,2);
insert into student values (null,'马六',26,2);

pojo类:

  • Classes 
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    privateInteger id;
    privateString  name;

    privateList<Student> students;
  • Student 
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    privateInteger id;
    privateString name;
    privateInteger age;

    privateList<Course> courses;//多对多时增加一个属性

interface接口:

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public interfaceOtmMapper {
//一对多
List<Classes> OtmSelectAll();
}

mapper映射:

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<mapper namespace="com.itheima.mapper.OtmMapper">
    <resultMap id="OneToMany" type="classes">
        <id column="cid" property="id"/>
        <result column="cname" property="name"/>
<!--        collection配置被包含的集合对象的映射关系
            property被包含对象的变量名
            ofType被包含对象的实际数据类型-->
<collection property="students" ofType="student">
            <id column="sid" property="id"/>
            <result column="sname" property="name"/>
            <result column="sage" property="age"/>
        </collection>
    </resultMap>
    <select id="OtmSelectAll" resultMap="OneToMany">
        select c.id cid,c.name cname,s.id sid,s.name sname,s.age sage
        from classes c,student s where s.cid=c.id;
    </select>

</mapper>

Test类：

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//一对多
@Test
public voidOtmSelectAll(){
        SqlSession sqlSession = SessionUtils.getSqlsession();

        OtmMapper mapper = sqlSession.getMapper(OtmMapper.class);
        List<Classes> classes = mapper.OtmSelectAll();

for(Classes c : classes) {
            System.out.println(c.getId()+"--"+c.getName());
            List<Student> students = c.getStudents();
for(Student s : students) {
                System.out.println(s);
            }
            System.out.println("================");
        }

        sqlSession.close();
}

执行结果:
1–黑马一班
Student{id=1, name=’张三’, age=23}
Student{id=2, name=’李四’, age=24}
================
2–黑马二班
Student{id=3, name=’王五’, age=25}
Student{id=4, name=’马六’, age=26}
================

3.多对多

mtm.jpg

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create table student(
                        id int primary key auto_increment,
                        name varchar(30),
                        age int,
                        cid int,
                        constraint cs_fk foreign key (cid) references classes(id)
);
insert into student values (null,'张三',23,1);
insert into student values (null,'李四',24,1);
insert into student values (null,'王五',25,2);
insert into student values (null,'马六',26,2);

create table course(
                        id int primary key auto_increment,
                        name varchar(30)
);
insert into course values (null,'语文');
insert into course values (null,'数学');

create table stu_cr(
                       id int primary key auto_increment,
                       sid int,
                       cid int,
                       constraint sc_fk1 foreign key (sid) references student(id),
                       constraint sc_fk2 foreign key (cid) references course(id)
);
insert into stu_cr values (null,1,1),(null,1,2),(null,2,1),(null,2,2);

pojo类：

  • Student 
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    privateInteger id;
    privateString name;
    privateInteger age;

    privateList<Course> courses;//多对多时增加一个属性
  • Course 
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    privateInteger id;
    privateString name;

interface接口:

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public interfaceMtmMapper {
    List<Student> mtmSelectAll();
}

mapper映射:

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<mapper namespace="com.itheima.mapper.MtmMapper">
    <resultMap id="manyToMany" type="student">
        <id column="sid" property="id"/>
        <result column="sname" property="name"/>
        <result column="sage" property="age"/>

        <collection property="courses" ofType="course">
            <id column="cid" property="id"/>
            <result column="cname" property="name"/>
        </collection>
    </resultMap>

    <select id="mtmSelectAll" resultMap="manyToMany">
        select sc.sid,s.name sname,s.age sage,sc.cid,c.name cname
        from student s,course c,stu_cr sc where sc.cid=c.id and sc.sid=s.id;
    </select>
</mapper>

Test类：

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//多对多
@Test
public voidmtmSelectAll(){
        SqlSession sqlSession = SessionUtils.getSqlsession();

        MtmMapper mapper = sqlSession.getMapper(MtmMapper.class);
        List<Student> stu = mapper.mtmSelectAll();

for(Student s : stu) {
            System.out.println(s.getId()+"--"+s.getName()+"--"+s.getAge());
            List<Course> cos = s.getCourses();
for(Course c : cos) {
                System.out.println(c);
            }
            System.out.println("================");
        }

        sqlSession.close();
}

运行结果:
1–张三–23
Course{id=1, name=’语文’}
Course{id=2, name=’数学’}
================
2–李四–24
Course{id=1, name=’语文’}
Course{id=2, name=’数学’}

4.小结

Untitled

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注意：本多表操作以查询作为演示，表中的外键字段并没有在实体类中体现。

二. MyBatis 注解实现多表操作

1.一对一

Untitled

  • pojo类 Card 
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    public classCard {
    privateInteger id;
    privateString number;

    privatePerson p;

    publicCard() {
        }

    publicCard(Integer id, String number, Person p) {
    this.id = id;
    this.number = number;
    this.p = p;
        }

    publicInteger getId() {
    returnid;
        }

    public voidsetId(Integer id) {
    this.id = id;
        }

    publicString getNumber() {
    returnnumber;
        }

    public voidsetNumber(String number) {
    this.number = number;
        }

    publicPerson getP() {
    returnp;
        }

    public voidsetP(Person p) {
    this.p = p;
        }

    @Override
    publicString toString() {
    return"Card{" +
                    "id=" + id +
                    ", number='" + number + '\'' +
                    ", p=" + p +
                    '}';
        }
    }

    Person 
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    public classPerson {
    privateInteger id;
    privateString name;
    privateInteger age;

    publicPerson() {
        }

    publicPerson(Integer id, String name, Integer age) {
    this.id = id;
    this.name = name;
    this.age = age;
        }

    publicInteger getId() {
    returnid;
        }

    public voidsetId(Integer id) {
    this.id = id;
        }

    publicString getName() {
    returnname;
        }

    public voidsetName(String name) {
    this.name = name;
        }

    publicInteger getAge() {
    returnage;
        }

    public voidsetAge(Integer age) {
    this.age = age;
        }

    @Override
    publicString toString() {
    return"Person{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

interface接口：

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public interface CardMapper {
    @Select("select * from card")
    @Results({
            @Result(column = "id",property = "id"),
            @Result(column = "number",property = "number"),
            @Result(
                    property = "p",   //被包含对象的变量名
                    javaType = Person.class,   //被包含对象的实际数据类型
                    column = "pid",   //根据查询出的card表中的pid字段来查询person表
                    /**
                     * one、@One 一对一固定写法
                     * select属性 指定调用哪个接口中的哪个方法
                    */
                      one=@One(select = "com.itheima.mapper.PersonMapper.selectById")
            )
    })
    List<Card> selectAll();
}

public interfacePersonMapper {
@Select("select * from person where id=#{id}")
    Person selectById(Integer id);
}

mapper映射文件（省略）

Test类：

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//注解一对一查询所有
@Test
public voidselectAll(){
    SqlSession sqlSession = SessionUtils.getSqlsession();

    CardMapper mapper = sqlSession.getMapper(CardMapper.class);
    List<Card> cards = mapper.selectAll();

for(Card c : cards) {
        System.out.println(c);
    }

    sqlSession.close();
}

查询结果：

Card{id=1, number=’12345’, p=Person{id=1, name=’张三’, age=23}}
Card{id=2, number=’23456’, p=Person{id=2, name=’李四’, age=24}}
Card{id=3, number=’34567’, p=Person{id=3, name=’王五’, age=25}}

2.一对多

Untitled

  • pojo类 Classes 
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    public classClasses {
    privateInteger id;
    privateString  name;

    privateList<Student> students;

    publicClasses() {
        }

    publicClasses(Integer id, String name, List<Student> students) {
    this.id = id;
    this.name = name;
    this.students = students;
        }

    publicInteger getId() {
    returnid;
        }

    public voidsetId(Integer id) {
    this.id = id;
        }

    publicString getName() {
    returnname;
        }

    public voidsetName(String name) {
    this.name = name;
        }

    publicList<Student> getStudents() {
    returnstudents;
        }

    public voidsetStudents(List<Student> students) {
    this.students = students;
        }

    @Override
    publicString toString() {
    return"Classes{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", students=" + students +
                    '}';
        }
    }
    Student 
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    public classStudent {
    privateInteger id;
    privateString name;
    privateInteger age;

    //private List<Course> courses;   //多对多时增加一个属性

    publicStudent() {
        }

    publicStudent(Integer id, String name, Integer age) {
    this.id = id;
    this.name = name;
    this.age = age;
        }

    /*public Student(Integer id, String name, Integer age, List<Course> courses) {
            this.id = id;
            this.name = name;
            this.age = age;
            this.courses = courses;
        }*/

        /*public List<Course> getCourses() {
            return courses;
        }

        public void setCourses(List<Course> courses) {
            this.courses = courses;
        }*/

    publicInteger getId() {
    returnid;
        }

    public voidsetId(Integer id) {
    this.id = id;
        }

    publicString getName() {
    returnname;
        }

    public voidsetName(String name) {
    this.name = name;
        }

    publicInteger getAge() {
    returnage;
        }

    public voidsetAge(Integer age) {
    this.age = age;
        }

    @Override
    publicString toString() {
    return"Student{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

interface接口：

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public interfaceClassesMapper {
//查询全部
@Select("select * from classes")
@Results({
@Result(column = "id",property = "id"),
@Result(column = "name",property = "name"),
@Result(
                    property = "students",//被包含对象的变量名
javaType = List.class,//被包含对象的实际数据类型
column = "id",//根据classes查询出的id字段来查询student表
/**
                     * many、@Many一对多固定写法
* select属性 指定调用哪个接口的哪个方法
*/
many =@Many(select = "com.itheima.mapper.StudentMapper.selectByCid")
            )
    })
    List<Classes> otmSelectAll();
}

public interface StudentMapper {
    //根据cid查询student表
    @Select("select * from student where cid = #{cid}")
    List<Student> selectByCid(Integer cid);
}

mapper映射文件（省略）

Test类：

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//注解一对多查询所有
@Test
public voidselectAll2() {
        SqlSession sqlSession = SessionUtils.getSqlsession();

        ClassesMapper mapper = sqlSession.getMapper(ClassesMapper.class);
        List<Classes> classes = mapper.otmSelectAll();

for(Classes c : classes) {
            System.out.println(c.getId()+"--"+c.getName());
            List<Student> students = c.getStudents();
for(Student s : students) {
                System.out.println("\t"+s);
            }
        }

        sqlSession.close();
}

查询结果：
1–黑马一班
Student{id=1, name=’张三’, age=23}
Student{id=2, name=’李四’, age=24}
2–黑马二班
Student{id=3, name=’王五’, age=25}
Student{id=4, name=’马六’, age=26}

3.多对多

Untitled

  • pojo类 Course 
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    public classCourse {
    privateInteger id;
    privateString name;

    publicCourse() {
        }

    publicCourse(Integer id, String name) {
    this.id = id;
    this.name = name;
        }

    publicInteger getId() {
    returnid;
        }

    public voidsetId(Integer id) {
    this.id = id;
        }

    publicString getName() {
    returnname;
        }

    public voidsetName(String name) {
    this.name = name;
        }

    @Override
    publicString toString() {
    return"Course{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    '}';
        }
    }

    Student 
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    public classStudent {
    privateInteger id;
    privateString name;
    privateInteger age;

    privateList<Course> courses;//多对多时增加一个属性

    publicStudent() {
        }

    publicStudent(Integer id, String name, Integer age) {
    this.id = id;
    this.name = name;
    this.age = age;
        }

    /*public Student(Integer id, String name, Integer age, List<Course> courses) {
            this.id = id;
            this.name = name;
            this.age = age;
            this.courses = courses;
        }*/

        /*public List<Course> getCourses() {
            return courses;
        }

        public void setCourses(List<Course> courses) {
            this.courses = courses;
        }*/

    publicInteger getId() {
    returnid;
        }

    public voidsetId(Integer id) {
    this.id = id;
        }

    publicString getName() {
    returnname;
        }

    public voidsetName(String name) {
    this.name = name;
        }

    publicInteger getAge() {
    returnage;
        }

    public voidsetAge(Integer age) {
    this.age = age;
        }

    @Override
    publicString toString() {
    return"Student{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

interface接口：

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public interface MtmStudentMapper {
    //查询student所有
    @Select("select distinct s.id,s.name,s.age from student s,stu_cr sc where sc.sid = s.id")
    @Results({
            @Result(column = "id",property = "id"),
            @Result(column = "name",property = "name"),
            @Result(column = "age",property = "age"),
            @Result(
                    property = "courses",  //被包含对象的变量名
                    javaType = List.class,    //被包含对象的实际数据类型
                    column = "id",    //根据查询出的student的id作为关联条件 ，去查询中间表和课程表
                    /**
                     * many、@Many 一对多固定写法   （中间表一对多）
                     * select属性 指定调用哪个接口中的哪个方法
                    */
                    many=@Many(select = "com.itheima.mapper.CourseMapper.selectById")
            ),
    })
    List<Student> mtmSelectAll();
}

public interface CourseMapper {
    //根据查询出的学生id查询课程信息
    @Select("select c.id,c.name from stu_cr sc,course c where sc.cid = c.id and sc.sid = #{id}")
    List<Course> selectById(Integer id);
}

mapper映射文件（省略）

Test类：

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//注解多对多查询所有
@Test
public voidselectAll3() {
        SqlSession sqlSession = SessionUtils.getSqlsession();

        MtmStudentMapper mapper = sqlSession.getMapper(MtmStudentMapper.class);
        List<Student> stu = mapper.mtmSelectAll();

for(Student s : stu) {
            System.out.println(s.getId()+"--"+s.getName()+"--"+s.getAge());
            List<Course> courses = s.getCourses();
for(Course c: courses) {
                System.out.println("\t"+c);
            }
        }

        sqlSession.close();
}

查询结果：

       1--张三--2
       Course{id=1, name='语文'}
       Course{id=2, name='数学'}
        2--李四--24
       Course{id=1, name='语文'}
       Course{id=2, name='数学'}

4.小结

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注意：本多表操作以查询作为演示，表中的外键字段并没有在实体类中体现。

三. 构建SQL

1.基本介绍

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2.代码示例：

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  • pojo类： 
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    public classStudent {
    privateInteger id;
    privateString name;
    privateInteger age;

    publicStudent() {
        }

    publicStudent(Integer id, String name, Integer age) {
    this.id = id;
    this.name = name;
    this.age = age;
        }

    publicInteger getId() {
    returnid;
        }

    public voidsetId(Integer id) {
    this.id = id;
        }

    publicString getName() {
    returnname;
        }

    public voidsetName(String name) {
    this.name = name;
        }

    publicInteger getAge() {
    returnage;
        }

    public voidsetAge(Integer age) {
    this.age = age;
        }

    @Override
    publicString toString() {
    return"Student{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

SqlReturn类：

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public classSqlReturn {
//返回查询SQL语句
publicString getSelectAll(){
return newSQL(){
            {
                SELECT("*");
                FROM("student");
            }
        }.toString();
    }

//返回插入SQL语句
publicString getInsert(){
return newSQL(){
            {
                INSERT_INTO("student");
                INTO_VALUES("#{id},#{name},#{age}");
            }
        }.toString();
    }

//返回修改SQL语句
//加条件判断  达到动态修改的效果
publicString getUpdate(Student stu){
return newSQL(){
            {
                UPDATE("student");

//加条件判断  达到动态修改的效果
if(stu.getName()!=null){
                    SET("name=#{name}");
                }
if(stu.getAge()!=null){
                    SET("age=#{age}");
                }

                WHERE("id=#{id}");
            }
        }.toString();
    }

//返回删除SQL语句
publicString getDelete(){
return newSQL(){
            {
                DELETE_FROM("student");
                WHERE("id=#{id}");
            }
        }.toString();
    }
}

接口StudentMapper类：

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public interfaceStudentMapper {
//@Select("select * from student")
@SelectProvider(type = SqlReturn.class,method = "getSelectAll")
    List<Student> getSelectAll();

//@Insert("insert into student values(#{id},#{name},#{age})")
@InsertProvider(type = SqlReturn.class,method = "getInsert")
    Integer inster(Student stu);

//@Update("update student set name=#{name},age=#{age} where id=#{id}")
@UpdateProvider(type = SqlReturn.class,method = "getUpdate")
    Integer update(Student stu);

//@Delete("delete from student where id=#{id}")
@DeleteProvider(type = SqlReturn.class,method = "getDelete")
    Integer delete(Integer id);
}

3.小结

2.jpg