mybatis select xml

配置文件中的 resultMap 标签有什么作用？

回答：在 mybatis 的 select xml 配置文件中，resultMap 标签用于映射 SQL 查询语句的返回结果与 Java 对象之间的关系，可以将查询结果的列名映射为对应 Java 对象的属性名，从而方便地将查询结果封装成 Java 对象。此外，resultMap 标签还可以定义关联查询、嵌套查询等复杂查询映射关系。

相关问题

mybatis mapper xml

MyBatis Mapper XML is a configuration file used in MyBatis, a Java-based persistence framework, to define SQL mappings between Java objects and database tables. The Mapper XML file contains SQL statements and mapping rules that are used to interact with the database.

In the Mapper XML file, you define the SQL statements such as SELECT, INSERT, UPDATE, DELETE, etc., using the MyBatis XML syntax. You also define the mapping rules to map the result of the SQL queries to Java objects or vice versa.

Here is an example of a simple Mapper XML file:

<?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.example.UserMapper">
    <select id="getUserById" resultType="com.example.User">
        SELECT * FROM users WHERE id = #{id}
    </select>
    <insert id="insertUser" parameterType="com.example.User">
        INSERT INTO users (id, name, email) VALUES (#{id}, #{name}, #{email})
    </insert>
    <update id="updateUser" parameterType="com.example.User">
        UPDATE users SET name = #{name}, email = #{email} WHERE id = #{id}
    </update>
    <delete id="deleteUser" parameterType="int">
        DELETE FROM users WHERE id = #{id}
    </delete>
</mapper>

In this example, the Mapper XML file defines four SQL statements: `getUserById`, `insertUser`, `updateUser`, and `deleteUser`. Each statement has an ID, parameterType (input parameter), resultType (output result mapping), and the actual SQL query.

You can then use the defined SQL statements in your Java code by referencing the Mapper XML file and the statement ID using MyBatis API.

Note that the actual mapping between Java objects and database tables is usually done through Java annotations or XML configuration files in addition to the Mapper XML file. The Mapper XML file primarily focuses on defining the SQL statements and their mappings.

I hope this gives you a basic understanding of MyBatis Mapper XML. Let me know if you have any further questions!

mybatis中xml配置

MyBatis是一个开源的持久层框架，它可以将数据库操作与Java对象之间的映射关系进行配置，提供了一种简单且灵活的方式来访问数据库。

在MyBatis中，XML配置文件是配置映射关系的主要方式。下面是一个简单的MyBatis XML配置文件的示例：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis_demo"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/example/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

上述配置文件中包含了以下几个重要的配置项：

1. `<environments>`：定义了环境配置，可以配置多个环境，通过`default`属性指定默认环境。
2. `<transactionManager>`：定义了事务管理器的类型，这里使用的是JDBC事务管理器。
3. `<dataSource>`：定义了数据源的类型和相关属性，这里使用的是连接池数据源（POOLED）。
4. `<mappers>`：定义了映射器（Mapper）的配置，可以通过`resource`属性指定映射器的XML文件路径。

在`<mappers>`标签中，可以通过`<mapper>`标签来引入映射器的配置文件。下面是一个简单的映射器配置文件的示例：

<?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.example.mapper.UserMapper">
    <select id="getUserById" resultType="com.example.model.User">
        SELECT * FROM user WHERE id = #{id}
    </select>
    <insert id="insertUser" parameterType="com.example.model.User">
        INSERT INTO user (id, name, age) VALUES (#{id}, #{name}, #{age})
    </insert>
    <update id="updateUser" parameterType="com.example.model.User">
        UPDATE user SET name = #{name}, age = #{age} WHERE id = #{id}
    </update>
    <delete id="deleteUser" parameterType="int">
        DELETE FROM user WHERE id = #{id}
    </delete>
</mapper>

上述映射器配置文件中定义了一些SQL语句，通过`<select>`、`<insert>`、`<update>`和`<delete>`标签来配置对应的SQL操作。其中，`id`属性指定了SQL语句的唯一标识，`parameterType`属性指定了参数类型，`resultType`属性指定了返回结果的类型。