One of the mybatis relational mappings is one of the many-to-many, one-to-one, and multiple-to-many.

One of the mybatis relational mappings is one of the many-to-many, one-to-one, and multiple-to-many.

I. Introduction:

This example describes how to use a customer and an order: a customer can have multiple orders, and an order only corresponds to one customer.

Ii. Example:

1. code structure:

2. Table creation statement:

CREATE DATABASE test;  USE test;CREATE TABLE person(  personId VARCHAR(36) PRIMARY KEY,  personName VARCHAR(64),  personAddress VARCHAR(128),  personTel VARCHAR(11));CREATE TABLE orders(  orderId VARCHAR(36) PRIMARY KEY,  orderNumber VARCHAR(20),  orderPrice INT,  pid VARCHAR(36));INSERT INTO person VALUES('001', 'Jack', 'Wuhan', '1234567');INSERT INTO orders VALUES('O_00001', '00001', 100, '001');INSERT INTO orders VALUES('O_00002', '00002', 200, '001');SELECT p.*, o.*FROM person p   JOIN orders o ON (p.personId=o.pid)WHERE p.personId = '001'

3. Customer entity:

/*** Customer entity */public class Person {private String id; private String name; private String address; private String tel; private List <Order> orders; @ Overridepublic String toString () {return "{id:" + id + ", name:" + name + ", address:" + address + ", tel: "+ tel + "}";}}

4. Order entity:

/*** Order entity */public class Order {private String id; private String number; private int price; private Person person Person; @ Overridepublic String toString () {return "{id: "+ id +", number: "+ number +", price: "+ price + "}";}}

5. One-to-Multiple object configuration: Person. xml

<? Xml version = "1.0" encoding = "UTF-8"?> <! DOCTYPE mapperPUBLIC "-// mybatis.org//DTD Mapper 3.0 //" http://mybatis.org/dtd/mybatis-3-mapper.dtd "> <mapper namespace =" com. zdp. domain. person "> <resultMap type =" Person "id =" personBean "> <id column =" personId "property =" id "/> <result column =" personName "property =" name "/> <result column =" personAddress "property =" address "/> <result column =" personTel "property =" tel "/> <! -- One-to-many relationship --> <! -- Property: the value of the Set property. ofType: indicates the type of elements in the collection --> <collection property = "orders" ofType = "Order"> <id column = "orderId" property = "id"/> <result column = "orderNumber" property = "number"/> <result column = "orderPrice" property = "price"/> </collection> </resultMap> <! -- Query Person by id and query Orders by Association --> <select id = "selectPersonById" parameterType = "string" resultMap = "personBean"> select p. *, o. * from person p, orders o where p. personId = o. pid and p. personId =#{ id} </select> </mapper>

6. Multiple-to-one instance Configuration:

<? Xml version = "1.0" encoding = "UTF-8"?> <! DOCTYPE mapperPUBLIC "-// mybatis.org//DTD Mapper 3.0 //" http://mybatis.org/dtd/mybatis-3-mapper.dtd "> <mapper namespace =" com. zdp. domain. order "> <resultMap type =" Order "id =" orderBean "> <id column =" orderId "property =" id "/> <result column =" orderNumber "property =" number "/> <result column =" orderPrice "property =" price "/> <! -- Multi-to-one relationship --> <! -- Property: indicates the property value. javaType: indicates the property type --> <association property = "person" javaType = "Person"> <id column = "personId" property = "id"/> <result column =" personName "property =" name "/> <result column =" personAddress "property =" address "/> <result column =" personTel "property =" tel "/> </association> </resultMap> <! -- Query Order by id and associate the query by Person --> <select id = "selectOrderById" parameterType = "string" resultMap = "orderBean"> select p. *, o. * from person p, orders o where p. personId = o. pid and o. orderId =#{ id} </select> </mapper>

7. Total configuration: sqlMapConfig. xml

<? Xml version = "1.0" encoding = "UTF-8"?> <! DOCTYPE configurationPUBLIC "-// mybatis.org//DTD Config 3.0 //" http://mybatis.org/dtd/mybatis-3-config.dtd "> <configuration> <typeAliases> <typeAlias type =" com. zdp. domain. person "alias =" Person "/> <typeAlias type =" com. zdp. domain. order "alias =" Order "/> </typeAliases> <environments default =" development "> <environment id =" development "> <transactionManager type =" JDBC "/> <dataSource type = "POOLED"> <property n Ame = "driver" value = "com. mysql. jdbc. driver "/> <property name =" url "value =" jdbc: mysql: // localhost/test "/> <property name =" username "value =" root "/> <property name =" password "value =" root "/> </dataSource> </environment> </environments> <mappers> <! -- Ing file location --> <mapper resource = "com/zdp/domain/Person. xml "/> <mapper resource =" com/zdp/domain/Order. xml "/> </mappers> </configuration>

8. Test file:

/*** Test one-to-many and multiple-to-one */public class MybatisTest {private SqlSessionFactory ssf; @ Beforepublic void initSF () throws Exception {String resource = "sqlMapConfig. xml "; InputStream inputStream = Resources. getResourceAsStream (resource); ssf = new SqlSessionFactoryBuilder (). build (inputStream) ;}@ Test // One-to-multiple association query public void selectPersonById () throws Exception {SqlSession session = ssf. openSession (); Person person = session. selectOne ("com. zdp. domain. person. selectPersonById "," 001 "); System. out. println (person. getOrders () ;}@ Test // public void selectOrderById () throws Exception {SqlSession session = ssf. openSession (); Order order = session. selectOne ("com. zdp. domain. order. selectOrderById "," O_00001 "); System. out. println (order. getPerson (). getName ());}}

Mybatis relational ing in Java, for example: one-to-many

There is no difference between using list and set. In most cases, set is used.
 
Hibernate annotations map the relationship between one-to-many and three tables. The existing three tables A, B, c a and B are one-to-many, and B and C are many-to-many.

Write a temporary Method
Public class {
Private Set <B> B;
Private Set <C> c; // here I want to use A to directly retrieve the Set of C. How should I write the link?
@ Transient
Public Set <C> getC (){
Set <C> cs = new HashSet <C> ();
If (B! = Null ){
For (B o: B ){
Cs. add (B. getC ());
}
}
Return cs;
}
}