Write MyBatis Dao layer

 

Preparation of traditional dao layer

Written before dao layer, first create a new package com.chy.dao, write interfaces StudentDao:

public interface StudentDao {
    public void insertStudent(Student student);

    public void updateStudent(Student student, Integer id);

    public Student selectStudent(Integer id);
}

 

Then write implementation class StudentDaoImpl:

public class StudentDaoImpl implements StudentDao {
    @Override
    public void insertStudent(Student student) {

    }

    @Override
    public void updateStudent(Student student, Integer id) {

    }

    @Override
    public Student selectStudent(Integer id) {
        return null;
    }
}

 

 

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Dao layer of the written MyBatis

MyBatis not write this dao. The dao MyBatis consists of two parts: mapping files, map files corresponding interface.

 

Create a new package com.chy.mapper, New Interface StudentMapper the package:

public interface StudentMapper {
    public void insertStudent(Student student);

    public Student selectStudent(Integer id);
}

 

This interface corresponding to the package under the new mapping file StudentMapper.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.chy.mapper.StudentMapper">
    <insert id="insertStudent" parameterType="com.chy.pojo.Student">
        INSERT INTO student_tb(name,age,score)VALUES (#{name},#{age},#{score})
    </insert>

    <select id="queryById" parameterType="Integer" resultType="Student">
        SELECT * FROM student_tb WHERE id=#{id}
    </select>
</mapper>

 

• Filename mapping file, namespace to interface with the same name, interface-oriented programming.
• id to be the same as the name of the method interface
• Parameter types, the return type for a consistent interface
• Interface methods can only have a maximum of parameters, because the parameter type mapping file can only have a

 

 

packet mapper equivalent conventional manner dao package mapping file corresponding to the interface implementation class.

 

 

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Use MyBatis dao layer

The introduction of mapping file in mybatis global configuration file.

　　　　 InputStream = Resources.getResourceAsStream the InputStream ( "MyBatis-the config.xml" ); 
        a SqlSessionFactory SqlSessionFactory = new new the SqlSessionFactoryBuilder () Build (inputStream);. 
        The SqlSession SQLSESSION = sqlSessionFactory.openSession (); 

        // call to the interface method by the mapper, the operation database 
        // parameter class object mapper interface classes 
        StudentMapper = sqlSession.getMapper mapper (StudentMapper.class); 

        // insert 
        Student student1 = new new Student (); 
        student1.setName ( "CHy" );
         mapper.insertStudent (student1);

         // query 
       Student student2 = mapper.queryById (1);
        System.out.println(student2);

        sqlSession.commit();
        sqlSession.close();

 

 

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Incoming package type parameter

Sometimes we need to pass multiple parameters, such as

• Query age> 20, score> 90 students need to pass two parameters of type Integer
• Query a book in sales this week, need to pass a pojo category: Book, also need to pass a parameter representation within this week.
• To query a user purchased a motor vehicle order information, need to pass two pojo categories: User, Car

This situation is more common multiple parameters passed in complex conditional queries, especially multi-table queries.

 

mybatis can pass up to one argument, how do?

Can be put to the parameters passed packaged, placed in a packaging, the packaging can be passed .

 

 

New Package com.chy.vo, under the new package wrapper class UserQueryVO, write parameters to be passed in as a member variable, and provides getter, setter methods:

public class UserQueryVO {
    private User user;
    private Car car;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }
}

vo: value object value object

po: persist object persistent object, corresponding to the data table.

pojo: plain ordinary java object simple Java objects

 

 

New interfaces at com.chy.mapper UserMapper packet, write the corresponding mapping file implement database operations.

public interface UserMapper {
    public Order queryOrder(UserQueryVO vo);
}

<mapper namespace="com.chy.mapper.UserMapper">
    <select id="queryOrder" parameterType="com.chy.vo.UserQueryVO" resultType="com.chy.pojo.Order">
        SELECT * FROM order_tb WHERE order_tb.user_id=#{user.id} AND order_tb.car_name=#{car.name}
    </select>
</mapper>

# {} In the user, CAR is vo property, the two properties are themselves objects, can be accessed by user., CAR properties.

 

 

use:

　　　　 InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession=sqlSessionFactory.openSession();

        Car car = new Car();
        car.setName("宝马X6");

        User user = new User();
        user.setId(1);

        //要传入的包装类
        UserQueryVO vo = new UserQueryVO();
        vo.setCar(car);
        vo.setUser(user);


        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //传入包装类进行查询
        Order order = mapper.queryOrder(vo);
        System.out.println(order);

 

 

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Using a number of parameters passed in Map

In addition to using a wrapper class pass multiple parameters, you can use Map pass multiple parameters.

 

Mapper interfaces:

public interface UserMapper {
    public Order queryOrder(Map<String,Object> map);
}

This is the Mapper interface, the interface parameters usually write, do not write a specific category, so that coupling is the interface level.

Different data types to be passed parameters, written in Object.

 

 

Mapping file:

<mapper namespace="com.chy.mapper.UserMapper">
    <select id="queryOrder" parameterType="HashMap" resultType="com.chy.pojo.Order">
        SELECT * FROM order_tb WHERE order_tb.user_id=#{user.id} AND order_tb.car_name=#{car.name}
    </select>
</mapper>

# {} In the user, car map is the key, obtain a corresponding value (the object), and then through. Getting a property value.

 

 

use:

　　　　 InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession=sqlSessionFactory.openSession();

        Car car = new Car();
        car.setName("宝马X6");

        User user = new User();
        user.setId(1);

        //要传入的包装类
        HashMap<String,Object> map = new HashMap<>();
        map.put("car", car);
        map.put("user", user);

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //传入map进行查询
        Order order = mapper.queryOrder(map);
        System.out.println(order);

 

Compared with the use of packaging a number of parameters passed in class, using the map need to create vo classes easier.