Mybatis study notes 1 Getting started with Mybatis_biubiubiu0706's blog-CSDN blog
Encapsulate Mybatis
SqlSessionUtil tool class
package com.example.util;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
/**
* @author hrui
* @date 2023/9/8 14:55
*/
public class SqlSessionUtil {
//工具类的构造方法一般都是私有化
//方法都是静态的
//为了防止new对象,构造方法私有化
private SqlSessionUtil(){
}
private static SqlSessionFactory sqlSessionFactory;
//类加载时候执行
//SqlSessionUtil工具类在被加载的时候,解析mybatis-config1.xml.创建sqlSessionFactory对象
static{
try {
SqlSessionFactoryBuilder sqlSessionFactoryBuilder=new SqlSessionFactoryBuilder();
//一个sqlSessionFactory对应一个数据库
sqlSessionFactory= sqlSessionFactoryBuilder.build(Resources.getResourceAsStream("mybatis-config1.xml"));
} catch (IOException e) {
e.printStackTrace();
}
}
//获取会话对象 返回会话对象
public static SqlSession openSession(){
SqlSession sqlSession = sqlSessionFactory.openSession();
return sqlSession;
}
}
This makes testing much more convenient
Create a new module mybatis-02-crud
maven project
Introduce dependencies
<!--引入mybatis依赖和mysql依赖-->
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.10</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.30</version>
</dependency>
<!--引入logback依赖-->
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.11</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13.2</version>
<scope>test</scope>
</dependency>
</dependencies>Copy the tool class and mybatis-config1.xml, logback.xml (log configuration file), xxxMapper.xml
The following writing method does not exist in actual development, and the values are hard-coded.
The object passed in is to encapsulate data and form a mapping relationship with #{xxx} in sql.
Try encapsulating it with Map. Write the key of the Map collection in #{}. What if the key does not exist? #{key does not exist} will be a null value.
Inserted successfully
Generally speaking, we will use the key as the corresponding relationship
The above is to pass the value through Map
The following provides set get, no parameters, full parameters, toString equal hashCode through value passing in the POJO class.
At this time, #{} is the attribute name of POJO (strictly speaking, XXX is converted to lowercase after the get method? I think it ignores the case and forms a mapping relationship. If the attribute name is written incorrectly, Map will insert null, but pojo If so, an error will be reported and the message There is no getter for property named 'xxxx' in class xxxxxxxx
It reported an error saying that the get method of the attribute could not be found.
Complete delete operation
If you pass a constant value directly #{You can write whatever you want}
Complete update operation
Query Check one
The id in the picture below is wrong. selectCarById
Note here that there is no need to commit when querying
Solution
1. Add an alias
2. Use resultMap
3. Configure to use camel case identifier
1. Add alias method:
2. Use resultMap
3. Use CamelCase
In the mybatis core configuration file
.XML
test
select search all
About the role of namespace in mapping files
Originally, the above tests only had one xxxMapper.xml mapping file.
When I have two .XML mapping files and the ids in them are the same
This way something will go wrong
test
In this situation
Multi-environment configuration in Mybatis core configuration file
About transaction management in Mybatis core configuration file
About DataSource------->DataSource is the specification of JDK. DataSource is simple to understand. It puts database connection.
Different properties under different types of DataSource
The role of JNDI: Let Mybatis use the connection pool of the container. The container implements the JNDI specification.
About the data source type UNPOOLED-->Not applicable to database connection pool--->Create a new Connection object each time
and POOLED---->use the database connection pool implemented by Mybatis itself
What are the specific differences regarding the above lights?
Create new libraries and tables in your local database
Core configuration file The default database uses connection pooling. Connection pooling is not applicable locally. See the specific differences.
If the test uses a connection pool, the connection object will be reused.
Test another database without connection pooling
Some configurations about database connection pool
What will happen when the connection is exhausted???????
It will wait for 20 seconds. After 20 seconds, it will force the connection to continue execution.
About the maximum number of free
About the preoperties tag in the core configuration file
Another use of properties
There is another way to write properties. The way to write url is also possible.
