mybatis Mapper文件查询返回map

在 MyBatis 的 Mapper 文件中，可以使用 `resultType="map"` 来指定查询结果的返回值类型为 Map。例如：

<select id="selectUserById" resultType="map">
  SELECT * FROM users WHERE id = #{id}
</select>

这样查询的结果将会是一个 Map 对象，其中键为列名，值为列对应的值。如果查询结果有多行，那么将会返回一个包含多个 Map 对象的 List。

需要注意的是，如果 Mapper 文件中指定了 `resultType`，那么查询结果的列名将会被转换为对应的 Java 对象的属性名。如果想要保留原始的列名，可以使用 `resultMap` 来自定义结果映射。

相关问题

mapstruct mapper 和mybatis mapper 冲突扫描不上

如果同时使用 MapStruct 和 MyBatis，可能会遇到 Mapper 扫描冲突的问题。这是因为两者都使用了 `@Mapper` 注解，并且默认的 Mapper 扫描路径也是相同的。

解决这个问题的方法是，为 MapStruct 的 Mapper 和 MyBatis 的 Mapper 指定不同的扫描路径。可以在启动类上使用 `@MapperScan` 注解，分别指定 MapStruct 和 MyBatis 的 Mapper 所在的包路径，例如：

@MapperScan(basePackages = "com.example.mapstruct.mapper", annotationClass = Mapper.class)
@org.mybatis.spring.annotation.MapperScan(basePackages = "com.example.mybatis.mapper", annotationClass = Mapper.class)
@SpringBootApplication
public class Application {
    // ...
}

上面的代码中，`@MapperScan` 注解中的 `basePackages` 属性分别指定了 MapStruct 和 MyBatis 的 Mapper 所在的包路径，`annotationClass` 属性指定了 Mapper 接口上所使用的注解类型。

这样就可以避免 Mapper 扫描冲突的问题了。

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!