Kotlin 实战小记：No-Arg 引用解决 No constructor found的问题

一、问题

新的项目试用一下kotlin, 调用数据库查询数据的时候报了这个问题：org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.executor.ExecutorException: No constructor found in com.neusoft.collect.entity.cm.CmRoom matching [java.lang.String, java.lang.String, java.lang.String, java.lang.Integer, java.lang.String, java.lang.Double, java.lang.Double]

二、原因

因为使用的是kotlin data class，通过mybatis查询返回不是data class中全部的字段，kotlin创建对象本身是没有无参构造器的，Java默认包含无参构造器；data class 是要返回所有字段，而业务不需要返回所有字段，这是问题出现的所在。

三、处理办法

通过引用No-Arg 插件，官网地址：No-arg compiler plugin | Kotlin Documentation

四、工程样例

注意：  <option>no-arg:annotation=com.neusoft.collect.config.NoArg</option> 和 创建的annotation class 路径保持一致

1、maven 部分引包

   <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>${java.version}</maven.compiler.source>
        <maven.compiler.target>${java.version}</maven.compiler.target>
        <springfox.swagger3.version>3.0.0</springfox.swagger3.version>
        <kotlin.version>2.0.0</kotlin.version>
    </properties>

   <dependencies>
      <dependency>
         <groupId>org.jetbrains.kotlin</groupId>
         <artifactId>kotlin-maven-noarg</artifactId>
         <version>${kotlin.version}</version>
       </dependency>
    </dependencies>

   <build>
        <plugins>
            <plugin>
                <artifactId>kotlin-maven-plugin</artifactId>
                <groupId>org.jetbrains.kotlin</groupId>
                <version>${kotlin.version}</version>
                <configuration>
                    <compilerPlugins> <!-- Or "jpa" for JPA support -->
                        <plugin>no-arg</plugin>
                    </compilerPlugins>
                    <pluginOptions>
                        <option>no-arg:annotation=com.neusoft.collect.config.NoArg</option>
                        <!-- Call instance initializers in the synthetic constructor -->
                        <!-- <option>no-arg:invokeInitializers=true</option> -->
                    </pluginOptions> </configuration>
            </plugin>
          
        </plugins>
    </build>

2、创建 annotation class

package com.neusoft.collect.config

/**
 * @author zc
 * @date 2024/06/18 10:31
 * @desc
 */
annotation class NoArg

3、data class 样例 引用 annotation class NoArg

package com.neusoft.collect.entity.cm


import com.neusoft.collect.config.NoArg
import java.io.Serializable

/**
 * @author zc
 * @date 2024/06/05 16:33
 * @desc 机房
 */
@NoArg
data class CmRoom(
    /**
     * 多云统一名称
     */
    var mc_uniform_name: String,

    /**
     * 详细地址
     */
    var detailed_address: String,

    /**
     * 机楼名称
     */
    var building_name: String,

    /**
     * 机房所在楼层
     */
    var floor: Int,

    /**
     * 机房房间号
     */
    var room_num: String,

    /**
     * 机房总行数
     */
    var row_count: Int?,

    /**
     * 机房总列数
     */
    var column_count: Int?,

    /**
     * 规划机架数
     */
    var project_rack_count: Int?,

    /**
     * 占用机架数
     */
    var occupation_rack_count: Int?,

    /**
     * 共用情况 枚举值：仅省级云使用、与其他业务共用
     */
    val share_statistic: String = "仅省级云使用",

    /**
     * 机房数据维护责任人
     */
    val data_maintain_vendor: String = "李剑春",

    /**
     * 关联资源池节点
     */
    var rel_res_pool_id: String,

    /**
     * 所属数据中心
     */
    val rel_dc_id: String = "JX001CPC-RP-JX-01",

    /**
     * 资源ID
     */
    var resource_id: String
): Serializable

4、mapper 样例： 返回部分字段

 /**
     * Room
     * 机房
     * @return
     */
    @Select(
        "SELECT  name AS mc_uniform_name," +
                " address AS detailed_address," +
                " building_name," +
                " floor," +
                " '001' AS room_num," +
                " CONCAT(#{province}, '004', pool_alias) AS rel_res_pool_id," +
                " CONCAT(#{province}, '002', instance_id) AS resource_id" +
                " FROM cm_room_t"
    )
    @Results(
        Result(property = "mc_uniform_name", column = "mc_uniform_name"),
        Result(property = "detailed_address", column = "detailed_address"),
        Result(property = "building_name", column = "building_name"),
        Result(property = "room_num", column = "room_num"),
        Result(property = "rel_res_pool_id", column = "rel_res_pool_id"),
        Result(property = "resource_id", column = "resource_id")
    )
    fun room(province: String): List<CmRoom>