1. 背景
mybatis最初配置信息是基于 XML ,映射语句(SQL)也是定义在 XML 中的。而到了 MyBatis 3提供了新的基于注解的配置。
这里讲述 注解开发方式:
首先我们需要获取 SqlSession:
SqlSession session = sqlSessionFactory.openSession(true);
参数设置为true表示开启自动提交模式。
session 在注解形式的使用方式如:
ClusterMessage clusterMessage = new ClusterMessage();
clusterMessage.setClusterId(1);
clusterMessage.setClusterName("useName");
clusterMessage.setClusterTime(new Date().getTime());
clusterMessage.setClusterAddress("localhost");
clusterMessage.setClusterAccessUser("user");
clusterMessage.setClusterAccessPasswd("test");
session.getMapper(ClusterMessageMapper.class).updateClusterMessage(clusterMessage);
所以mybatis 的使用使用三部分:
- 数据查询主体 :
SqlSession - 查询映射层 :
Mapper接口 - 数据维护层 :
Bean 设计
2. 案例
table :
CREATE TABLE cluster_manager(
cluster_id int PRIMARY KEY AUTO_INCREMENT ,
cluster_name VARCHAR(20) NOT NULL,
cluster_time BIGINT NOT NULL ,
cluster_address VARCHAR(50) NOT NULL,
cluster_access_user VARCHAR(50) NOT NULL ,
cluster_access_passwd VARCHAR(50) NOT NULL
)AUTO_INCREMENT=0;
Bean :
public class ClusterMessage {
int clusterId = 0; // 集群ID
String clusterName = ""; // 集群名称
Long clusterTime = 0l; // 集群上线时间
String clusterAddress = ""; // 集群内网访问地址
String clusterAccessUser = ""; // 集群访问用户
String clusterAccessPasswd = ""; // 集群访问密码
public int getClusterId() {
return clusterId;
}
public void setClusterId(int clusterId) {
this.clusterId = clusterId;
}
public String getClusterName() {
return clusterName;
}
public void setClusterName(String clusterName) {
this.clusterName = clusterName;
}
public Long getClusterTime() {
return clusterTime;
}
public void setClusterTime(Long clusterTime) {
this.clusterTime = clusterTime;
}
public String getClusterAddress() {
return clusterAddress;
}
public void setClusterAddress(String clusterAddress) {
this.clusterAddress = clusterAddress;
}
public String getClusterAccessUser() {
return clusterAccessUser;
}
public void setClusterAccessUser(String clusterAccessUser) {
this.clusterAccessUser = clusterAccessUser;
}
public String getClusterAccessPasswd() {
return clusterAccessPasswd;
}
public void setClusterAccessPasswd(String clusterAccessPasswd) {
this.clusterAccessPasswd = clusterAccessPasswd;
}
@Override
public String toString() {
return "ClusterMessage{" +
"clusterId='" + clusterId + '\'' +
", clusterName='" + clusterName + '\'' +
", clusterTime=" + clusterTime +
", clusterAddress='" + clusterAddress + '\'' +
", clusterAccessUser='" + clusterAccessUser + '\'' +
", clusterAccessPasswd='" + clusterAccessPasswd + '\'' +
'}';
}
}
Mapper:
public interface ClusterMessageMapper {
// Insert
@Insert("insert into cluster_manager(cluster_name, cluster_time, cluster_address, cluster_access_user, cluster_access_passwd) " +
"values(#{clusterName}, #{clusterTime}, #{clusterAddress}, #{clusterAccessUser}, #{clusterAccessPasswd})")
@Options(useGeneratedKeys = true, keyColumn = "cluster_id", keyProperty = "clusterId")
public void insertClusterMessage(ClusterMessage clusterMessage);
// select
@Select("select * from cluster_manager")
@Results(
id = "clusterMessage",
value = {
@Result(column = "cluster_name", property = "clusterName", javaType = String.class, jdbcType = JdbcType.VARCHAR),
@Result(column = "cluster_time", property = "clusterTime", javaType = Long.class, jdbcType = JdbcType.BIGINT),
@Result(column = "cluster_address", property = "clusterAddress", javaType = String.class, jdbcType = JdbcType.VARCHAR),
@Result(column = "cluster_access_user", property = "clusterAccessUser", javaType = String.class, jdbcType = JdbcType.VARCHAR),
@Result(column = "cluster_access_passwd", property = "clusterAccessPasswd", javaType = String.class, jdbcType = JdbcType.VARCHAR)
}
)
public List<ClusterMessage> getClusterMessage();
@Select("select * from cluster_manager")
@MapKey("clusterId")
public Map<Integer, ClusterMessage> getClusterMessageMapper();
@Select("select * from cluster_manager where cluster_id=#{clusterId}")
@ResultMap("clusterMessage")
public ClusterMessage getClusterMessageById(@Param("clusterId") int clusterId);
// update
@Update("update cluster_manager set cluster_name=#{clusterName} where cluster_id=#{clusterId}")
public void updateClusterMessage(ClusterMessage clusterMessage);
// delete
@Delete("delete from cluster_manager where cluster_id=#{clusterId}")
public void deleteClusterMessage(@Param("clusterId")int clusterId);
}
3. 详解:
这里主要讲解 Mapper 层的开发规则。
sql 类型主要分成 : select@Select(${sql}), update@Update(${sql}), insert@Insert($sql), delete(${sql}).
@Select:
@Results 用来设置table信息与bean相关字段的映射关系， 每一个字段的关系使用 @Result控制。
默认情况下对于每一table字段，例如name, 会调用 bean 中的 setName(..). 如果找不到，对于新版本的 mybatis 会报错。
例如上面的 cluster_name 会调用 setCluster_name(). 但是java 中使用的 clusterName,可以通过 Result 注解控制.
@ResultMap 可以通过Id,应用其他的Results
还有一种更改映射的方式:
TransactionFactory transactionFactory = new JdbcTransactionFactory();
Environment environment = new Environment(DEVELOPMENT, transactionFactory, dataSource);
Configuration configuration = new Configuration(environment);
configuration.setMapUnderscoreToCamelCase(true);
mapUnderscoreToCamelCase 设置为true, 之后会自动实现 mysql 中的unix命名方式转为java的驼峰表示法。
@MapKey 此注解应用将查询数据转为 Map<>, 注意的是MapKey()中的id最终调用bean的getId 获取数据，所以需要映射bean字段而不是table.
@Param注解:
@Param注解用于给方法参数起一个名字。以下是笔者总结的使用原则：
在方法只接受一个参数的情况下，可以不使用@Param。
在方法接受多个参数的情况下，建议一定要使用@Param注解给参数命名。
@Insert :
insert 时获取自增主键的方式:
法一:
@Options(useGeneratedKeys = true, keyColumn = "cluster_id", keyProperty = "clusterId")
法二:
@SelectKey(statement="SELECT LAST_INSERT_ID()", keyProperty="clusterId", before=false, resultType=Integer.class)
4. #与$的区别:
#{} 的作用主要是替换预编译语句(PrepareStatement)中的占位符?:
对于 : INSERT INTO user (name) VALUES (#{name}); ==> INSERT INTO user (name) VALUES (?);
${} 符号的作用是直接进行字符串替换:
对于 : INSERT INTO user (name) VALUES ('${name}'); ==> INSERT INTO user (name) VALUES ('tianshozhi');
