Day15 Mybatis关联查询

一对一：返回单条数据

mapper.xml

<resultMap id="Login" type="User">
        <id  column="u_id" property="u_id"></id>
        <result column="u_name" property="u_name"></result>
        <result column="u_password" property="u_password"></result>
        <result column="u_type" property="u_type"></result>
        <result column="u_datatime" property="u_datatime"></result>
        <!-- column :列名   property : 字段名-->
    </resultMap>
    
    <select id="findUser" parameterType="User" resultMap="Login">
        select * from user where u_name=#{u_name} and u_password=#{u_password}
    </select>

dao

public User findUser(User user);

一对一：返回多条数据

userMapper.xml

 <resultMap id="LoginList" type="User">
        <id property="u_id" column="u_id"></id>
        <result column="u_name" property="u_name"></result>
        <result column="u_password" property="u_password"></result>
        <result column="u_type" property="u_type"></result>
        <result column="u_datatime" property="u_datatime"></result>
    </resultMap>

<select id="findUserList" resultMap="LoginList" parameterType="User">
        select * from user where u_name=#{u_name} and u_password=#{u_password}
    </select>

dao

public List<User> findUserList(User user);

一对多

 <resultMap id="LoginMap" type="Order"><!-- type 父实体类-->
        <id  column="u_id" property="u_id"></id>
        <collection property="user" ofType="User"><!--property:  取出来的数据的类型 ofType: 子实体类类型-->
            <id  column="u_id" property="u_id"></id>
            <result column="u_name" property="u_name"></result>
            <result column="u_password" property="u_password"></result>
            <result column="u_type" property="u_type"></result>
            <result column="u_datatime" property="u_datatime"></result>
        </collection>
</resultMap>
<select id="findOrder" resultMap="LoginMap" parameterType="User">
        select * from user,user_type where user.u_type = user_type.u_t_id and user.u_type=#{u_type};
 </select>

dao

public List<Order> findOrder(User user);

pojo实体类

Order

package com.ssm.pojo;

public class Order {
    
    
    private int u_id;
    private User user;

    public int getU_id() {
    
    
        return u_id;
    }

    public void setU_id(int u_id) {
    
    
        this.u_id = u_id;
    }

    public User getUser() {
    
    
        return user;
    }

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

User

package com.ssm.pojo;

public class User {
    
    
    private int u_id;
    private String u_name;
    private String u_password;
    private  int u_type;
    private String u_datatime;

    public int getU_id() {
    
    
        return u_id;
    }

    public void setU_id(int u_id) {
    
    
        this.u_id = u_id;
    }

    public String getU_name() {
    
    
        return u_name;
    }

    public void setU_name(String u_name) {
    
    
        this.u_name = u_name;
    }

    public String getU_password() {
    
    
        return u_password;
    }

    public void setU_password(String u_password) {
    
    
        this.u_password = u_password;
    }

    public int getU_type() {
    
    
        return u_type;
    }

    public void setU_type(int u_type) {
    
    
        this.u_type = u_type;
    }

    public String getU_datatime() {
    
    
        return u_datatime;
    }

    public void setU_datatime(String u_datatime) {
    
    
        this.u_datatime = u_datatime;
    }

    @Override
    public String toString() {
    
    
        return "User{" +
                "u_id=" + u_id +
                ", u_name='" + u_name + '\'' +
                ", u_password='" + u_password + '\'' +
                ", u_type=" + u_type +
                ", u_datatime='" + u_datatime + '\'' +
                '}';
    }
}