mybatis之级联关系（一对一对多）
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0. 表结构
1. 准备工作
1.1 配置文件等信息，请参考 myBatis之入门示例
1.2 entity
1.2.1 TPersonInfo.java
package com.blueStarWei.entity; public class TPersonInfo { private Integer id; private String name; private Integer age; private Address address; //setter & getter @Override public String toString() { return "TPersonInfo [id=" + id + ", name=" + name + ", age=" + age + ", address=" + address + "]"; } }
1.2.2 Address.java
package com.blueStarWei.entity; public class Address { private int id; private String country; private String city; //setter & getter @Override public String toString() { return "Address [country=" + country + ", city=" + city + "]"; } }
2 一对一关系(Maper)
2.1 方法一：
2.1.1 PersonAddressMapper.java
package com.blueStarWei.mappers; import java.util.List; import com.blueStarWei.entity.TPersonInfo; public interface PersonAddressMapper { List<TPersonInfo> findAllWithAddress(); }
2.1.2 PersonAddressMapper.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.blueStarWei.mappers.PersonAddressMapper"> <select id="findAllWithAddress" resultMap="personResult"> SELECT t1.*,t2.* FROM t_person_info t1 JOIN t_address t2 ON t2.id = t1.addressid </select> <resultMap type="TPersonInfo" id="personResult"> <id property="id" column="id"/> <result property="name" column="name"/> <result property="age" column="age"/> <association property="address" resultMap="addressResult"/> </resultMap> <resultMap type="Address" id="addressResult"> <id property="id" column="id"/> <result property="country" column="country"/> <result property="city" column="city"/> </resultMap> </mapper>
2.2 方法二【推荐】
2.2.1 AddressMapper.java
package com.blueStarWei.mappers; import com.blueStarWei.entity.Address; public interface AddressMapper { public Address findById(Integer id); }
2.2.2 AddressMapper.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.blueStarWei.mappers.AddressMapper"> <select id="findById" parameterType="Integer" resultMap="addressResult"> SELECT * FROM t_address t where t.id = #{id} </select> <resultMap type="Address" id="addressResult"> <id property="id" column="id"/> <result property="country" column="country"/> <result property="city" column="city"/> </resultMap> </mapper>
2.2.3 PersonMapper.java
package com.blueStarWei.mappers; import java.util.List; import com.blueStarWei.entity.TPersonInfo; public interface PersonMapper { TPersonInfo findById(Integer id); List<TPersonInfo> findAll(); }
2.2.4 PersonMapper.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.blueStarWei.mappers.PersonMapper"> <select id="findById" parameterType="Integer" resultMap="personResult"> select * from t_person_info a where a.id = #{id} </select> <select id="findAll" resultMap="personResult"> select * from t_person_info </select> <resultMap type="TPersonInfo" id="personResult"> <id property="id" column="id"/> <result property="name" column="name"/> <result property="age" column="age"/> <association property="address" column="addressid" select="com.blueStarWei.mappers.AddressMapper.findById"/> </resultMap> </mapper>
2.3. 总结：
方法一是使用级联的方式查找出需要的所有信息，然后将结果返回到对应的entity类中，方法二是通过外键关联的方式返回结果。方法二在开发过程中被推荐时间，因为其具有代码高复用性。
3 一对多关系
3.1 Family.java
package com.blueStarWei.entity; import java.util.List; public class Family { private Integer id; private String familyCode; private List<TPersonInfo> persons; //setter & getter @Override public String toString() { return "Family [id=" + id + ", familyCode=" + familyCode + ", persons=" + persons + "]"; } }
3.2 FamilyMapper.java
package com.blueStarWei.mappers; import com.blueStarWei.entity.Family; public interface FamilyMapper { Family findById(Integer id); }
3.3 FamilyMapper.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.blueStarWei.mappers.FamilyMapper"> <select id="findById" parameterType="Integer" resultMap="familyResult"> SELECT * FROM t_family t where t.id = #{id} </select> <resultMap type="Family" id="familyResult"> <id property="id" column="id"/> <result property="familyCode" column="familyCode"/> <collection property="persons" column="id" select="com.blueStarWei.mappers.PersonMapper.findByFamilyId"/> </resultMap> </mapper>
3.4 PersonMapper.java
package com.blueStarWei.mappers; import java.util.List; import com.blueStarWei.entity.TPersonInfo; public interface PersonMapper { List<TPersonInfo> findByFamilyId(Integer familyId); }
3.5 PersonMapper.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.blueStarWei.mappers.PersonMapper"> <select id="findByFamilyId" parameterType="Integer" resultMap="personResult"> select * from t_person_info a where a.familyId = #{familyId} </select> <resultMap type="TPersonInfo" id="personResult"> <id property="id" column="id"/> <result property="name" column="name"/> <result property="age" column="age"/> <association property="address" column="addressid" select="com.blueStarWei.mappers.AddressMapper.findById"/> </resultMap> </mapper>
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