MyBatis之基於XML的表之間映射
數據庫表之間的關系有3種,一對一、一對多、多對多。既然是ORM,這肯定是必須有的。在學習EF的時候也有涉及,今天就是參考著EF的來學習下MyBatis的表關系映射。
一、準備工作
1.準備Model和Table
既然是要涉及表的一對一、一對多、多對多的關系,那肯定得先準備好實體關系,以及表。下面建了四個對象四個表。User<->Card是一對一關系,User<->Course一對多關系,User<->Role多對多關系。
User
CREATE TABLE `user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `NAME`View Codevarchar(20) DEFAULT NULL, `age` int(11) DEFAULT NULL, `status` varchar(20) DEFAULT ‘0‘, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8;
package Cuiyw.MyBatis.Model; import java.util.List; public class User { @Override public String toString() {View Code// TODO Auto-generated method stub return "User [id=" + Id + ", name=" + Name + ", age=" + Age + ",status="+Status+"]"; } public int getId() { return Id; } public void setId(int id) { Id = id; } public String getName() { return Name; }public void setName(String name) { Name = name; } public int getAge() { return Age; } public void setAge(int age) { Age = age; } private int Id; private String Name; private int Age; private UserState Status; private Card card; public Card getCard() { return card; } public void setCard(Card card) { this.card = card; } private List<Role> roles; private List<Course> courses; public List<Course> getCourses() { return courses; } public void setCourses(List<Course> courses) { this.courses = courses; } public List<Role> getRoles() { return roles; } public void setRoles(List<Role> roles) { this.roles = roles; } public UserState getStatus() { return Status; } public void setStatus(UserState status) { this.Status = status; } }
Card
CREATE TABLE `card` ( `id` int(11) NOT NULL AUTO_INCREMENT, `cardNo` varchar(20) NOT NULL, `city` varchar(45) NOT NULL, `address` varchar(100) NOT NULL, `userid` int(11) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;View Code
package Cuiyw.MyBatis.Model; public class Card { @Override public String toString() { // TODO Auto-generated method stub return "Card [id=" + getId() + ", cardNo=" + cardNo + ", city=" + city + ",address="+address+",userid="+userid+"]"; } private int id; private String cardNo; private String city; private String address; private int userid; public int getUserid() { return userid; } public void setUserid(int userid) { this.userid = userid; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getCardNo() { return cardNo; } public void setCardNo(String cardNo) { this.cardNo = cardNo; } public String getCity() { return city; } public void setCity(String city) { this.city = city; } }View Code
Course
CREATE TABLE `course` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(45) NOT NULL, `userid` int(11) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;View Code
package Cuiyw.MyBatis.Model; public class Course { @Override public String toString() { // TODO Auto-generated method stub return "Course [id=" + getId() + ", name=" + name +",userid="+userid+"]"; } private int id; private String name; private int userid; public int getUserid() { return userid; } public void setUserid(int userid) { this.userid = userid; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } }View Code
Role
CREATE TABLE `role` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(45) NOT NULL, `desp` varchar(45) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;View Code
package Cuiyw.MyBatis.Model; import java.util.List; public class Role { @Override public String toString() { // TODO Auto-generated method stub return "Role [id=" + getId() + ", name=" + name +",desp="+desp+"]"; } private int id; private String name; private String desp; private List<User> users; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getDesp() { return desp; } public void setDesp(String desp) { this.desp = desp; } public List<User> getUsers() { return users; } public void setUsers(List<User> users) { this.users = users; } }View Code
User_Role
CREATE TABLE `user_role` ( `userid` int(11) NOT NULL, `roleid` int(11) NOT NULL, PRIMARY KEY (`userid`,`roleid`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;View Code
2.準備映射
上一篇博客是單個表的映射關系,我們也先把但表的映射準備好。
<resultMap type="Card" id="cardResult"> <result column="id" property="id"/> <result column="no" property="cardNo"/> <result column="city" property="city"/> <result column="address" property="address"/> <result column="userid" property="userid"/> </resultMap> <resultMap type="Course" id="courseResult"> <result column="id" property="id"/> <result column="name" property="name"/> <result column="userid" property="userid"/> </resultMap> <resultMap type="Role" id="roleResult"> <result column="id" property="id"/> <result column="name" property="name"/> <result column="desp" property="desp"/> <result column="userid" property="userid"/> </resultMap>View Code
二、關系映射
加入我們需要執行下面的sql查詢數據,那怎麽映射到實體model上呢?
<select id="getuser" parameterType="int" resultType="User" resultMap="userResult"> select a.id as user_id,a.name as user_name,a.age as user_age,a.status as user_status, b.id as card_id,b.cardNo as card_cardNo,b.userid as card_userid, b.city as card_city,b.address as card_address,c.id as course_id,c.name as course_name, c.userid as course_userid,e.name as role_name,e.desp as role_desp from user a left join card b on a.id=b.userid left join course c on a.id=c.userid left join user_role d on a.id=d.userid left join role e on d.roleid=e.id where a.id=#{id} </select>View Code
我們可以這樣寫來映射User。
<resultMap type="User" id="userResult"> <result column="user_id" property="id"/> <result column="user_name" property="name"/> <result column="user_age" property="age"/> <result column="user_status" property="status" typeHandler="Cuiyw.MyBatis.Model.ValuedEnumTypeHandler"/> <association property="card" javaType="Card" columnPrefix="card_"> <result column="id" property="id"/> <result column="no" property="cardNo"/> <result column="city" property="city"/> <result column="address" property="address"/> <result column="userid" property="userid"/> </association> <collection property="courses" javaType="ArrayList" ofType="Course" columnPrefix="course_"> <result column="id" property="id"/> <result column="name" property="name"/> <result column="userid" property="userid"/> </collection> <collection property="roles" javaType="ArrayList" ofType="Role" columnPrefix="role_"> <result column="id" property="id"/> <result column="name" property="name"/> <result column="desp" property="desp"/> <result column="userid" property="userid"/> </collection> </resultMap>View Code
上面的xml種有兩個重要的節點。
association關聯:關聯的結果查詢,就是在查詢出結果後,根據查詢的列和resultMap定義的對應關系,來創建對象並寫入值,例如user的card屬性。
collection:用來映射class中的List列表類型的屬性。
還有就是JavaType和ofType:JavaType和ofType都是用來指定對象類型的,但是JavaType是用來指定pojo中屬性的類型,而ofType指定的是映射到list集合屬性中pojo的類型。
三、優化
上面的xml配置確實可以映射User,但是在映射Card、Course和Role的時候把映射關系都放在的id=userResult的resultMap中,這樣如果以後還有要映射Card、Course、Role的時候還要再寫一遍,復用性不高。其實我們可以在association和collection節點增加屬性resultMap。
<resultMap type="User" id="userResult"> <result column="user_id" property="id"/> <result column="user_name" property="name"/> <result column="user_age" property="age"/> <result column="user_status" property="status" typeHandler="Cuiyw.MyBatis.Model.ValuedEnumTypeHandler"/> <association property="card" javaType="Card" resultMap="cardResult" columnPrefix="card_"></association> <collection property="courses" javaType="ArrayList" ofType="Course" resultMap="courseResult" columnPrefix="course_"></collection> <collection property="roles" javaType="ArrayList" ofType="Role" resultMap="roleResult" columnPrefix="role_"></collection> </resultMap>View Code
而resultMap的值正是我們上面單表準備的映射resultMap。
四、驗證
//mybatis的配置文件 String resource = "Config.xml"; //使用MyBatis提供的Resources類加載mybatis的配置文件(它也加載關聯的映射文件) Reader reader = Resources.getResourceAsReader(resource); //構建sqlSession的工廠 SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader); //創建能執行映射文件中sql的sqlSession SqlSession session = sessionFactory.openSession(true); // System.out.println("新增"); String statement="Cuiyw.MyBatis.DBMapping.UserMapper.addUser"; System.out.println("查詢單個"); statement="Cuiyw.MyBatis.DBMapping.UserMapper.getuser"; User user=session.selectOne(statement, 2); Card card=user.getCard(); List<Course>courses=user.getCourses(); List<Role>roles=user.getRoles(); session.close(); System.out.println(user.toString()); System.out.println(card.toString()); for(int i=0;i<courses.size();i++) { System.out.println(courses.get(i).toString()); } for(int i=0;i<roles.size();i++) { System.out.println(roles.get(i).toString()); }View Code
五、總結
這篇主要是學習表的關系映射,association、collection的使用,上面演示了一對一、一對多,對於多對多,可以把它當作兩個一對多,這裏只是演示了User對Role的一對多,Role對User的也是一樣,這裏就省了。具體可以參考官網:http://www.mybatis.org/mybatis-3/zh/sqlmap-xml.html
MyBatis之基於XML的表之間映射