Master One-to-One and One-to-Many MyBatis Mappings with Real-World Examples

1. One-to-One

Scenario: In everyday life each person has an ID card, representing the simplest one-to-one relationship.

(1) User table

(2) ID card table

(3) User entity class,

com.xuliugen.mybatis.demo.bean.User

(4) ID card entity class,

com.xuliugen.mybatis.demo.bean.Card

(5) User table XML mapping file

<code><!-- One-to-one relationship mapping --> <association column="card_id" property="card" select="com.xuliugen.mybatis.demo.dao.CardMapper.selectByPrimaryKey" javaType="com.xuliugen.mybatis.demo.bean.Card"/> </code>

Key points (highlighted in red):

1. column indicates the card_id field in the user table; 2. property indicates the card attribute in the User entity; 3. select uses the column value as the parameter for the method; 4. javaType specifies the returned object type.

(6) ID card table XML mapping file

(7) Test Controller

(8) Test result

2. One-to-Many

Scenario: In everyday life each class has multiple students, representing the simplest one-to-many relationship.

(1) Student table

Here, clazz_id represents the class ID.

(2) Class table

(3) Class entity class

(4) Student entity class

(5) Class table XML mapping file

Key points (highlighted in red):

1. fetchType indicates lazy loading; choose eager or lazy . Typically one-to-many associations are set to lazy loading; 2. property indicates the attribute in the parent entity that holds the collection; 3. select uses the column value as the method parameter; 4. javaType specifies the returned object type.

(6) Student table XML mapping file

(7) Test Controller

(8) Test result

Conclusion

If you need the code, download it from Baidu Cloud:

http://pan.baidu.com/s/1jItB8HK password: slti